Jones & Bartlett Learning CDX Automotive Sample Chapter 32 by Jones & Bartlett Learning

SAMPLE

CHAPTER 32 DISC BRAKE SYSTEM

FUNDAMENTALS OF

Automotive Technology ÂŠ SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

Principles and Practice

Meets 2012 NATEF Automobile Accreditation Standards

Get in gear in

ÂŠ SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

Change is in the air. As you know, the new National Automotive Technicians Education Foundation (NATEF) Automobile Accreditation Model was approved by the NATEF Trustees and National Institute of Automotive Service Excellence (ASE) Board of Directors. The 2012 NATEF Automobile Accreditation Model and the accompanying 2012 NATEF Automobile Accreditation Task Lists focus on the future of the automotive industry: more preventative maintenance and fewer repairs.

Dear Educator,

The 2012 NATEF Automobile Accreditation Model is intended to promote clarification of responsibilities by introducing three levels of training: Maintenance & Light Repair (MLR), Auto Service Technology (AST), and Master Auto Service Technology (MAST). By grouping Task Lists by level, the goal is to promote consistency of training across programs and to promote learning through active experience as opposed to learning through passive listening. In addition, the three distinct levels provided by the 2012 NATEF Automobile Accreditation Model provide students with a set list of marketable skills. CDX is using the 2012 NATEF Automobile Accreditation Model and 2012 NATEF Automobile Accreditation Task Lists to develop a complete teaching and learning system: Fundamentals of Automotive Technology: Principles and Practice. Students and instructors will have the tools to build a solid, knowledgeable foundation with world-class automotive content. Cutting-edge digital and online resources expand upon and reinforce this foundation, creating skilled technicians.

Let us help you redefine your automotive courses.

with CDX! The Fundamentals of Automotive Technology: Principles and Practice teaching and learning system will include: n Printed textbook – Fundamentals of Automotive Technology

will be the first training program that completely and concisely covers the entire 2012 NATEF Automobile Accreditation Task Lists. Presented in an approachable writing style, this highlydeveloped manual will feature an unparalleled level of casebased learning tools, including detailed step-by-step pictorial skill drills.

n eBook/eWorkbook – With the content of Fundamentals of

Automotive Technology at your students’ fingertips, students will be able to take notes, test their knowledge of automotive systems, watch animations and videos, and perfect their understanding of key psychomotor skills. The interactive eWorkbook will hone students’ critical thinking skills and analyze their comprehension of critical content.

n Web Tools – Additional interactive and mobile educational

resources such as a complete audio book in mp3 format, chapter pretests, interactive skill drills, and skill evaluation sheets will be available.

n Learning Management System – With this powerful online

tool, instructors will be able to manage assignments, enjoy automatic grading, and facilitate discussions.

n Test Prep – This dynamic tool will help prepare students for

ASE Certification Tests by providing practice examinations and simulated certification examinations using ASE-style questions and detailed rationales.

n Interactive Course Content – Online modules that cover

the entire scope of the 2012 NATEF Automobile Accreditation Task Lists will be available. The modules will provide anytime, anywhere access for students in a safe and self-paced training environment that will allow students to learn at their own convenience and pace.

n Personalized Adaptive Learning (PAL) – The shift to

competency-based education is driving the need for more sophisticated digital tools. PAL will help educators determine competency.

Contact your CDX Account Manager or visit www.cdxauto.com to get started.

What steps are CDX the 2012 NATEF Automobile

Just remember that the brake lights will stay on if Fundamentals of Automotive Technology will offer instructors you don’t pull the brake light fuse. (Step 3) and students comprehensive coverage of every NATEF Task in an 5 Remove the brake line or hose from the caliper. Be engaging and accessible format. careful not to lose the two brake hose copper (or

and damage to the caliper housing, and determine any

aluminum) sealing rings, if equipped. (Step 4) 6 Push the caliper pistons back into their bores slightly. Use of a small pry bar or C-clamp will usually force the piston back just far enough so that the caliper can be removed from the pads and rotor once the caliper is loose from its mount. (Step 5) 7 Remove the caliper assembly from its mountings, willfollowing the service manual procedure. Be careful this help me in the shop?” Through concrete examples in to avoid dislodging brake dust, which may contain each chapter, Fundamentals of Automotive Technology gives asbestos. (Step 6) students a genuine context for the application of the knowledge 8 Inspect the caliper for leaks or damage, including presented in the chapter. This approach makes it clear how all of the piston dust boot. this new information will be used in the 7) shop. 9 Determine any necessary actions. (Step

For the last several years, CDX Automotive has been SKILLproducing SKILL DrILL 32-1 : necessary actions, follow the steps in Research the procedure for removing the caliper 1 that allow student-directed learning and innovative materials

hybrid courses. Now we are taking these tools to the next level and adding a printed resource for students. With Fundamentals of removed, you might want to use a brake pedal Automotive Technology: Principles and Practice, CDX will offer a holding tool to slightly apply the brakes and block complete and learning system. off the cteaching ompensating ports in the master cylinder.

vi BrakeS We have gathered22 a teamsection of outstanding educators from across the country to help create a complete teaching and learning system of the rotors on the vehicle, removal of the rotors for using CDX’s Know-See-Do-Prove model. In addition to developing replacement, or machining of the rotors off the vehicle. a gold standard student resource, we are building a wide range of Further, it allows for a thorough inspection of the caliper, teaching and learning tools that will enable instructors to achieve pads, and rotor to determine the cause of a brake congreater individualcern. To remove the caliper assembly, inspect for leaks creativity in course design.

in the appropriate service information. Follow this procedure. The following steps are general in nature and should not be substituted for the manufacturer’s specifi c procedure. 2 If the caliper is likely to be reinstalled on the vehicle or rebuilt and reinstalled, it is good practice to loosen the bleeder screws slightly and then retighten them. Doing so ensures that they are A Relaxed, Readable Textbook – When writing automotive not seized in place and that they will be able to be textbooks, authors often forget who their audience really is. loosened later when bleeding the system. Failure to Fundamentals of Automotive Technology will create a learning do this now could waste a lot of time later trying to repair a bleeder screw when it breaks off. (Step 1) environment in which students are comfortable with the material If the caliper is being rebuilt or a new caliper will 3 presented. That comfort level translates into better understanding be installed, it is good practice to fl ush the old and retention, and ultimately leads to better pass rates. This brake fl uid from the system at this time, so that old textbook talks to yourbrake fl students, not at them. uid will not have to be bled through the new or newly rebuilt caliper. Also, leave the masClear Application of to Real-World Situations – ter Material cylinder reservoir level low so that pushing the istons into their bores will not overfl Students who want tocaliper enter pthe automotive field are hands-on. ow the rinformation eservoir. (Stepis2) important to learn. “How They need to know why draining 4 To minimize the amount of brake fl uid out of the brake lines or hoses when they are

Students Will Enjoy

SKILL DRILL

appropriate service information. Loosen the bleeder screws slightly and then retighten them.

24118_CH32_Pass6.indd 22

technology is constantly TECHNICIAN TIP changing. The content of Fundamentals of Automotive Technology reflects the guidance and Some technicians pinch off the ﬂ exible brake hoses recommendations of an extremely experienced, geographically with vice grip pliers. This should be avoided because it diverse group of authors. crimps the hose, potentially damaging it internally and/ or externally.

Removing and Inspecting Calipers

32-1

Research the procedure for

removing the caliper in the

Current, State-of-the-Art Content – Automotive

If the caliper is being rebuilt or

a new caliper will be installed, it is good practice to flush the old brake fluid from the system at this time.

Use a brake pedal holding tool to

slightly apply the brakes and block off the compensating ports in the master cylinder to avoid excess fluid leakage.

Let us help you redefine your automotive courses.

27/06/12 5:24 PM

taking to implement Accreditation Task Lists? Instructors Will Enjoy

decades of experience in both automotive technology and in the education of future automotive technicians. This textbook is clearly written by one of us, for all of us.

Constant Reinforcement of Concepts – Instructors are concerned about the 2012 NATEF Automobile Accreditation Task List and its impact on their classrooms. Fundamentals of Automotive Technology eases any transition to the new 2012 NATEF Automobile Accreditation Task Lists.

A Textbook That Reflects the Expertise of its Author Team – The authors are seasoned automotive instructors with

Clear Application of Material to Real-World Situations – Instructors will find countless opportunities

to place their students “in the shop” with case studies, video products that show automotive technicians in action, and critical thinking examination tools. Opportunities to apply knowledge ultimately make students better-equipped automotive technicians. And isn’t that our goal: to teach students how to be great automotive technicians?

Fundamentals is the cornerstone of a complete teaching and learning system consisting of ample resources for both student and faculty. With online resources, students and faculty are able to take practice tests, work on module assignments, and use TestPrep to ensure competency. Instructors will enjoy the updated presentations, test banks, and learning management system. This system provides an outstanding platform for a dynamic learning environment for all students.

Contact your CDX Account Manager or visit www.cdxauto.com to get started.

NATEF Tasks Brakes

General Brake Systems

CHAPTER 32

Describe procedure for performing road test to check brake system operation, including an anti-lock brake system (ABS).

Page 19

Hydraulic System n

Diagnose poor stopping, pulling or dragging concerns caused by malfunctions in the hydraulic system; determine necessary action.

Disc Brakes

n n

Diagnose poor stopping, noise, vibration, pulling, grabbing, dragging or pulsation concerns; determine necessary action.

Remove and clean caliper assembly; inspect for leaks and damage/wear to caliper housing; determine necessary action.

20–23

Clean and inspect caliper mounting and slides/pins for proper operation, wear, and damage; determine necessary action.

23–24

Check brake pad wear indicator; determine necessary action.

23–25

Remove, inspect and replace pads and retaining hardware; determine necessary action.

Lubricate and reinstall caliper, pads, and related hardware; seat pads and inspect for leaks.

26–28

Retract and readjust caliper piston on an integrated parking brake system.

28–29

Clean and inspect rotor, measure rotor thickness, thickness variation, and lateral runout; determine necessary action.

30–32

Remove and reinstall rotor.

32–34

NATEF Tasks, continued

Disc Brake System Refinish rotor on vehicle; measure final rotor thickness and compare with specifications.

34–36

Refinish rotor off vehicle; measure final rotor thickness and compare with specifications.

35–38

The applicable Inspect and replace drive axle 2012 wheelAutomobile studs. (NATEF, Drive Axles)

39–41

Accreditation Task List along with the chapter’s Knowledge n Install wheel and torque lug nuts. (NATEF, Drum Brakes) and Skill Objectives are listed at n Describe importance of operating vehicle to burnish/break-in replacement the beginning of each chapter brake pads according tocorresponding manufacturer’s levels recommendations. with the and page references.

Knowledge Objectives

After reading this chapter, you will be able to: 1. Describe the components of the disc brake system. (pp 6–8) 2. Describe how the components of the disc brake system work together during braking operations. (pp 6–7) 3. Describe the advantages and disadvantages of the disc brake system. (pp 7–8) 4. Describe the purpose of disc brake calipers. (pp 8–11) 5. Describe the components of disc brake calipers. (pp 9–11) 6. Describe the purpose of disc brake pads. (pp 11–15) 7. Describe the principle of the coefficient of friction and how it affects brake lining materials. (pp 12–15) 8. Describe the components that are employed to prevent noise in disc brakes. (pp 14–15) 9. Describe the types of wear indicators for disc brakes. (pp 15–16) 10. Describe the purpose of disc brake rotors. (pp 16–17) 11. Describe the types of disc brake rotors. (p 17) 12. Describe how the parking brake system operates in a disc brake system. (pp 18–19) 13. Describe the types of parking brakes in a disc brake system. (pp 18–19) 14. Describe the process of diagnosing issues with a disc brake system. (pp 19–43)

39–43 39–43

SECTION VI BRAKES

After reading this chapter, you will be able to: 1. Remove and inspect the caliper. (pp 20–23) 2. Inspect caliper mountings, slides, and pins. (pp 23–24) 3. Inspect brake pads and wear indicators. (pp 23–25) 4. Check the brake pads. (p 25) 5. Disassemble the caliper. (pp 25–26) 6. Reassemble the caliper. (pp 26–28) 7. Retract and readjust the piston on an integrated parking brake. (pp 28–29) 8. Inspect and measure the disc brake rotor. (pp 30–32) 9. Remove and reinstall the disc brake rotor. (pp 32–34) 10. Refinish the disc brake rotor while it is on the vehicle. (pp 34–36) 11. Refinish the disc brake rotor while it is off the vehicle. (pp 35–38) 12. Inspect and replace wheel studs. (pp 39–41) 13. Install a wheel, torque lug nuts, and make final checks and adjustments. (pp 39–43)

Skills Objectives

chapter 32 Disc Brake System

introduction Strong– No Deflection Heavy Pressure

Moderate Pressure

Not as Strong– Deflection

isc (also spelled disk) brakes are so named because D they create braking power by forcing fl at friction pads against the sides of a rotating disc. This disc is also called a disc brake rotor, or rotor. The vehicle wheels are bolted to the disc FIGURE 32-1 . The applied force is created in the caliper, which straddles the pads and rotor. Higher applied forces can be used in disc brakes than in drum brakes, because the design of the rotor is stronger than the design of the drum FIGURE 32-2 . Since heat is generated on the outside surfaces of the rotor, it can be easily transferred to the atmosphere. Disc brakes are effective at

FIGURE 32-2 32-2 Disc versus drum brakes.

creating substantial braking power using a fairly simple design that is relatively easy for technicians to service and repair.

TECHNICIAN TIP

FIGURE 32-1 32-1 Disc brake operation.

he purpose of the disc brake system is to provide an T effective means to slow the vehicle under a variety of conditions in an acceptable distance and manner. The better a braking system can do this, the more likely the vehicle will avoid an accident.

You are the Automotive Technician

a customer comes into the service department. She has been experiencing a pulsating brake pedal and high pitched sqealing during braking on her 2009 Town and Country minivan, which has 41,000 miles on the odometer. after reviewing the vehicle’s service history on your computer, you notice the vehicle has never had any brake service. You advise the customer that you will need to complete a more thorough inspection to determine what is causing the issues. after completing a visual inspection of the brakes, and measurement of the rotor’s thickness and parallelism, you see that the front brake linings have worn down to the wear indicators and the rotors are warped beyond specifi cations. You inform the customer of your fi ndings and recommend that the vehicle needs new front brake pads installed, and the rotors refi nished. You also recommend that the brake fl uid be fl ushed, since the fl uid is beyond the end of its two-year life. 1. What conditions can cause a rotor to become warped? 2. What conditions would require replacement of the rotors rather than just refi nishing them? 3. What are the relatively common maximum specifi cations for rotor runout and thickness variation? Case Studies capture students’ attention and offer an authentic context for students to apply their knowledge.

section vi BrakeS

Purpose and Overview isc brakes operate on the same principle as all friction D brakes. They generate stopping power by applying friction materials to moving surfaces, thus transforming the vehicle’s kinetic energy into heat energy. This is accomplished by disc brake calipers using hydraulic pressure from the master cylinder to create a mechanical clamping action, forcing the brake pads onto the surface of the rotor, creating friction. As the vehicle’s kinetic energy is transformed into heat energy, the vehicle’s speed decreases.

to provide a clamping force on a rotor that is attached to the wheel hub. This clamping action is designed to stop the rotation of the rotor and the wheel. The rotors are free to rotate with the wheels due to wheel bearings and the hubs that contain them. The hub can be part of the brake rotor or a separate assembly that the rotor slips over and is bolted to by the lug

Disc Brake system

Key Terms are easily identified and odern passenger vehicles are almost always equipped M defined with the text. A list of Key with disc brakes on at least the front two wheels, and Terms concludes each chapter, many manufacturers are using them on all four wheels. and a comprehensive glossary The primary components of the disc brakes are: appears at the end n R otor of the textbook. n C aliper n B rake pads FIGURE 32-3 The rotors are the main rotating part of this brake are the main rotating part of this brake system. They are durable and resist being damaged by the high temperatures that occur during braking. In highperformance vehicles, the rotors are made from composite FIGURE 32-3 32-3 The disc brake system. materials, ceramics, or carbon fi ber; otherwise, they are usually made of cast iron. The caliper straddles the rotor and houses the disc brake pads and an activating piston(s). The calipers use hydraulic pressure from the master cylinder to apply the brake pads. They are usually bolted to the steering knuckle or, in the case of a nonsteering axle, to a suspension component. Calipers need to be inspected at the same time as the brake pads. T he disc brake pads are located inside the caliper or caliper mounting bracket. The pads clamp onto the rotor to slow or stop the vehicle. The disc brake pad consists of a friction material bonded or riveted to a steel backing plate. With this design, the pads will wear out over time and need to be replaced periodically. Master cylinder

Disc Brake Operation

isc brakes can be used on all four wheels of a vehicle, D or a combination of brake types can be used, with disc brakes on the front wheels and drum brakes on the rear. When the brake pedal is depressed, a pushrod transfers the force through a brake booster to a hydraulic master cylinder. The master cylinder converts the pedal force into hydraulic pressure, which is then transmitted via brake lines and hoses to one or more pistons at each brake caliper FIGURE 32-4 . The pistons operate on friction pads

Pedal

Secondary Primary piston piston

FIGURE 32-4 32-4 The master cylinder converts the pedal force into hydraulic pressure, which is then transmitted via brake lines and hoses to one or more pistons at each brake caliper.

chapter 32 Disc Brake System

keeping the wheels on the ground, especially on uneven road surfaces. isc brake pads require much higher application D pressures to operate than drum brake shoes because they are not self-energizing. This additional clamping pressure is created by increasing the diameter of the caliper pistons. Unfortunately, this means the brake pedal travel is lengthened to move the additional fl uid being displaced by the larger caliper pistons. Building in more pushrod travel would require more room under the dash. Manufacturers have overcome this problem by equipping most disc brake systems with a power booster. Because of the high forces needed to apply a disc brake, using it as a parking brake is more challenging. Some manufacturers have chosen to design more complicated calipers, while others have built an auxiliary drum brake assembly into the center of the rear disc brake rotors to provide for parking brake operation. This is referred to as a top hat design.

nuts FIGURE 32-5 . On rear-wheel drive vehicles, the rotor is mounted onto the driving axle or hub and may be held in place by the wheel. On front-wheel drive vehicles, it can be mounted on the front hub and wheel bearing assembly. The brake caliper assembly is normally bolted to the vehicle axle housing or suspension FIGURE 32-6 . In most cases, the brake is positioned as close as possible to the wheel, but there are exceptions. Some high- performance cars with independent rear suspension (IRS) use inboard disc brakes on the rear wheels. The calipers are mounted on or next to the differential, which is directly mounted to the vehicle body. Manufacturers claim improved vehicle handling for this design because it reduces the vehicle’s unsprung weight by taking the differential assembly and brakes from the suspension and mounting them to the body. Because the wheels and axles are now lighter, the vehicle’s springs can do a better job of

Advantages and Disadvantages

FIGURE 32-5 32-5 The hub and hubless rotors.

FIGURE 32-6 32-6 Caliper mounting methods.

isc brakes have a number of advantages over drum D brakes. They also have some disadvantages. In most cases, the advantages outweigh the disadvantages. One of the biggest advantages is that disc brakes can generate and transfer greater amounts of heat to the atmosphere; because most of the friction area of a rotor is exposed to air, cooling is far more rapid than for a drum brake. This faster cooling makes them better suited for highperformance driving or heavy-duty vehicles and reduces the likelihood of brake fade. A lso, because of their shape, rotors tend to scrape off water more effectively. After being driven through water, disc brakes operate at peak performance almost immediately. Further, due to their design, disc brakes are self-adjusting and do not need periodic maintenance or rely on a self-adjusting mechanism that is prone to sticking (see the Disc Brake Calipers section). Lastly, in most cases, disc brakes are also easier to service than drum brakes. W hile disc brakes have a number of benefi ts over drum brakes, there are some disadvantages. Probably the most apparent disadvantage is that disc brakes are much more prone to noise. Their design tends to create squeals and squeaks, which can be very annoying. Many a technician has spent time servicing perfectly functional disc brakes due to excessive noise complaints. Another issue is that the rotors warp easier than in drum brake systems. Since the brake pads are pressing on each side of the rotor, thickness variations of as small as 0.0003" (0.0076 mm) can cause brake

section vi BrakeS

TECHNICIAN TIP

hile there may appear to be more disadvantages W to disc brakes versus drum brakes, the advantages are generally considered much more critical than the disadvantages. Thus, disc brakes are preferred over drum brakes in most applications.

ydraulic pressure forces the pistons on both sides of h the caliper inward, causing the brake pads to come in contact with the rotor FIGURE 32-9 . Once the pad-to-rotor c learance is taken up, the hydraulic pressure rises equally on each side of the caliper, applying both brake pads equally. The sliding or fl oating caliper has brake pads located on each side of the rotor, but all of the pistons are only on one side, usually the inside of the rotor. Thus, the ydraulic force is generated on one side of the rotor, but h the unique design applies equal braking force to both sides of the rotor. This distribution of force is possible because the caliper is mounted on pins, or slides, that allow it to move (fl oat or slide) from side to side as necessary. This movement allows pistons on one side of the rotor to generate force on both sides of the rotor at the same time.

pedal pulsations, requiring resurfacing or replacement. The last disadvantage is that since disc brakes are not self-energizing, they need higher clamping forces, which requires a power booster. This also makes it harder to use them as effective parking brakes.

Disc Brake calipers

I n most applications, the disc brake caliper assembly is bolted to the vehicle axle housing, or steering knuckle , and clamps the brake pads onto the rotors to slow the vehicle. There are two main types of calipers: fixed calipers and sliding or floating calipers FIGURE 32-7 . Sliding or fl oating calipers are the most common type used in passenger vehicles because they are easier to build and are more compact. All calipers are fi tted with a bleeder screw on the top of the piston bore to allow for the removal of air within the disc brake system as well as to help in performing routine brake fl uid changes. F ixed calipers are rigidly bolted in place and cannot move or slide. This makes their application of braking forces more precise than fl oating calipers. They c ommonly have one to four pistons on each side of the rotor FIGURE 32-8 . When the brakes are applied,

FIGURE 32-7 32-7 Fixed and sliding/floating calipers.

FIGURE 32-8 32-8 Fixed calipers with multiple pistons.

FIGURE 32-9 32-9 Fixed caliper being applied.

chapter 32 Disc Brake System

I n disc brake calipers, the piston is sealed by a stationary square section sealing ring, also called a square cut O-ring FIGURE 32-11 . This O-ring has a square crosssection and is fi tted in a machined groove in the caliper. The O-ring is compressed between the piston and

O-Rings

caliper housing, creating a positive seal to keep the high-pressure brake fluid from leaking out. It also prevents air from being drawn into the system when a low-pressure situation is created in the hydraulic system when the brake pedal is released quickly. hen the brakes are applied, the piston moves W outward, slightly deforming the O-ring seal FIGURE 32-12 . When the brakes are released, the elasticity or fl exibility of the seal causes it to return to its original shape. This action of the sealing ring retracts the piston to provide a small running clearance between the rotor and pads. As the brake pads wear, the piston needs to move outward a bit farther than the sealing ring can stretch or fl ex. The sealing ring is designed to allow the piston to slide through it in this situation, taking up the extra clearance and making the disc brakes self-adjusting.

hen the brakes are applied, hydraulic pressure W f orces the piston toward the rotor. This takes up any clearance between the brake pad and rotor and starts to push the pad into the rotor. Since the caliper is free to move on the pins or slides, it gets pushed away from the rotor, pulling the outer brake pad into contact with the outside of the rotor. Once all clearance is taken up on the outer brake pad, the clamping force will increase equally on both brake pads, applying the brakes FIGURE 32-10 .

Text that prepares students for the shop.

TECHNICIAN TIP

S ince the force generated by the O-ring to retract the piston is fairly small, any corrosion or buildup on the piston or bore will cause the piston to stick and not retract. This holds the brakes in the applied position, causing brake drag, overheated brakes, and poor fuel economy. Technicians can identify this situation by using an infrared temperature gun to measure the temperature of each brake rotor after test-driving the vehicle. The temperatures should be approximately the same on each side. If they are not, suspect a stuck or binding caliper.

FIGURE 32-10 32-10 Sliding/floating caliper application.

O-ring groove in caliper

FIGURE 32-11 32-11 A. Square cut O-ring and O-ring cut to show square section. B. Square cut O-ring groove in caliper.

section vi BrakeS

FIGURE 32-12 32-12 A. Square cut O-ring during brake application. B. Square cut O-ring during brake release.

Highly descriptive and detailed illustrations enable the student to free of pitting or rust; therefore, steel pistons are chrome visualize automotive systems and plated. This gives the surface a hard, wear-resistant, and mechanical concepts.

Seal travel Low drag caliper

Seal travel Standard caliper

corrosion-resistant fi nish. Chrome can still rust, but it is much more corrosion resistant than steel. Another way manufacturers have dealt with the corrosion issue is by making pistons out of a phenolic resin . Pool balls also are made from phenolic resin, which is very dense when it hardens and does not corrode or rust, making for a good sealing surface in brake systems. Although the phenolic pistons themselves do not corrode, the cast iron bore of the caliper does corrode and rust and can therefore cause a phenolic piston to seize in the bore FIGURE 32-14 .

FIGURE 32-13 32-13 Low-drag caliper.

Some calipers, sometimes called low-drag calipers , are designed to maintain a larger brake pad-to-rotor clearance by retracting the pistons a little bit farther. This is accomplished by modifying the sealing groove in the caliper so the outside of the groove is slightly angled toward the rotor FIGURE 32-13 . This position allows the seal to fl ex a bit farther upon brake application and then retract the piston a greater distance. These systems use a “quick take-up” or “fast fi ll” master cylinder to maintain adequate brake pedal reserve height. T he primary sealing surface is the outside diameter of the piston. It is critical that this surface be smooth and

FIGURE 32-14 32-14 Corroded caliper piston bore.

FIGURE 32-16 32-16 Floating caliper guide pins.

Phenolic pistons transfer heat slower than steel istons FIGURE 32-15 , which is a good thing because they p transfer less heat from the brake pad to the brake fl uid. This helps prevent boiling of the brake fl uid in the caliper under heavy brake usage. Calipers with phenolic pistons are therefore less susceptible to brake failure from boiling brake fl uid. There is also a dust boot that seals the surfaces of the piston and caliper bore from outside dirt and moisture. This seal connects to both the piston and the caliper and must be expandable to allow the piston to move outward as the brake pads wear. It also must be free from cuts and holes; otherwise the piston and bore could corrode and cause the piston to bind in the bore, causing brake drag.

chapter 32 Disc Brake System

Caliper Lubrication

loating calipers are mounted in place by guide pins F and bushings FIGURE 32-16 . The pins allow the caliper to move in and out as the brakes are operated and as the brake pads wear. Since the calipers move on the pins, the bushings must be lubricated with high-temperature, w aterproof disc brake caliper grease when they are serviced. This will help prevent them from binding or sticking. Inspecting, cleaning, and lubricating the pins and pin bores, including any bushings and dust boots, are important steps in disc brake repair. Sliding calipers have matching machined surfaces on the caliper and caliper mount that allow the caliper to slide in the mount FIGURE 32-17 . The sliding mount holds the caliper in position and prevents it from rotating when the brakes are applied. The machined mounts allow the caliper to move side to side as necessary to operate the brakes or adjust for brake pad wear. The surfaces must be

FIGURE 32-17 32-17 Sliding caliper.

cleaned and lubricated with the same high-temperature, waterproof grease as the fl oating calipers when the calipers are serviced. Sliding calipers are held in place by a spring steel clip or shim that is bolted to the caliper mount.

Disc Brake Pads and Friction Materials

FIGURE 32-15 32-15 A. Phenolic piston (slow heat transfer) B. Steel piston (fast heat transfer)

isc brake pads consist of friction material bonded D or r iveted onto a steel b acking plate FIGURE 32-18 . Bonded linings are more common on light-duty vehicles since they are less expensive to build and the bonding agent can fail under the very high temperatures of heavy-duty use. Riveted linings are used on heavier-duty or highperformance vehicles. Metal rivets provide a mechanical connection to hold the lining to the backing plate that is less susceptible to failure under high temperatures. Since the rivets actually pinch some of the lining between the rivet head and the backing plate, the linings must be changed sooner than bonded linings. Otherwise, the

section vi BrakeS

FIGURE 32-19 32-19 Brake pad locating lugs.

FIGURE 32-18 32-18 Bonded and riveted brake pads.

rivet heads would contact the rotor and wear a groove in the face of the rotor. The backing plate has lugs that correctly position the pad in the caliper assembly and help the backing plate maintain the proper position to the rotor FIGURE 32-19 . Disc brakes are usually designed so that the thickness of the pads can be checked easily once the wheel has been removed. Most disc brakes also are designed to allow the pads to be replaced with a minimum of disassembly. S ome pads have a groove cut into the friction surface. This groove helps ventilate gases that build up at the surface of the friction material under heavy brake application. It also can help modify the harmonic vibration quality of the friction material to reduce brake squeal. On some pads, the depth of this groove is set so that as the pad wears thinner, the remaining groove gets smaller; when it can no longer be seen, the pad should be replaced. The composition of the friction material affects brake operation. Materials that provide good braking with low pedal pressures tend to lose effi ciency when they get hot, thus increasing the stopping distance. They also tend to wear out quicker. Materials that maintain a stable friction coeffi cient over a wide temperature range generally require higher pedal pressures to provide effi cient braking. They also tend to put added wear on the disc brake rotor, reducing its useful life FIGURE 32-20 .

Brake Friction Materials riction is the force that acts to prevent two surfaces in F contact from sliding against each other. The amount of friction between two surfaces is expressed as a ratio and is called the coeffi cient of friction. When friction occurs, the kinetic energy (motion) of the sliding surfaces is converted into thermal energy (heat). Some combinations of materials, such as a hockey puck on ice, have a very low coeffi cient of friction. There is very little friction between

FIGURE 32-20 32-20 Brake rotor wear.

them and therefore almost no sliding resistance. Rubber tires against a dry hard road surface have a high coeffi cient of friction, which means they tend to grip and resist sliding against each other. Disc brake pads and drum brake linings are made from materials that have a moderate coeffi cient of friction TABLE 32-1 . They also must be able to absorb and TABLE 32-1: Brake Lining Coefﬁ cient of Friction (Sliding) Materials Involved

Coefﬁcient of Friction—Dry Sliding

rubber and concrete Steel and cast iron Copper and cast iron Brass and cast iron Leather and oak Brake lining (FF rating)

.6–.85 .23 .29 .3 .52 .35–.45

chapter 32 Disc Brake System

applied

Math

Safety

Don’t assume that a brake pad doesn’t contain asbestos; AM-17: Charts/Tables/Graphs: The technician can it is still found in some applications. interpret charts, tables, and graphs to determine the manufacturer’s specifications for a given system. algebra (9–12) Safety Tips reinforce safety and n Ceramic materials—Ceramic fi ber materials and C3: Draw reasonable conclusions about a situation being injury prevention concepts. modeled. possibly a small amount of copper r epresentation The choice of brake lining compound depends on the a2: Select, apply, and translate among mathematical application. Lighter passenger vehicles generate less heat representations to solve problems. in the brakes than heavy or high-performance vehicles. T echnicians regularly apply math concepts to disc Living in a very hilly region of the country, or where there brake diagnosis and repair. For example, a technician will measure the amount of rotor thickness variation is a lot of stop-and-go traffi c, will put added demands and runout if there is a brake pedal pulsation problem. on the brake pads. The optimum brake composition for Let’s say the technician performed these measurements any given vehicle or use is a combination of weighted and came up with a thickness variation of 0.0025" qualities, including: (0.064 mm) and a runout of 0.0015" (0.038 mm) on n S topping power the left front rotor. Next the technician looks up the n H eat absorption and dispersion manufacturer’s specifi cation chart and found that the maximum allowable thickness variation is 0.0005" n R esistance to fade (0.013 mm) and the maximum allowable runout is n R ecovery speed from fade 0.003" (0.076 mm) for the vehicle being worked on. n W ear rate Using the information from the chart, the technician n P erformance when wet determines that the thickness variation is excessive n O perating noise by 0.002" (0.051 mm) (0.0025" [0.064 mm] – 0.0005" n P rice [0.013 mm] = 0.002" [0.051 mm]) and the runout is Ok since it is under the maximum allowable specifi cation. For instance, owners of small economy vehicles tend But even so, since the thickness variation is out of to value a longer pad life and minimal operating noise specifi cations, the rotor will need to be refi nished or rather than resistance to fade in extreme conditions. replaced to bring it back within specifi cation.

d isperse large amounts of heat without their braking performance being adversely affected. As the heat in brake pads and linings builds up, the coeffi cient of friction capability of the material—and consequently its stopping power—is reduced. This is called brake fade. Minimizing or overcoming fade is a major factor in the design of brakes and the development of brake friction materials. Brake friction materials were historically made from asbestos compounds because of the excellent heat resistance of that material. Now that asbestos has been proven to be toxic, it is generally banned and is not normally used. Today, brakes are manufactured from a variety of different materials, including: n Non-asbestos organic (NAO) materials—Organic materials such as Kevlar and carbon n Low-metallic NAO materials—Small amounts of copper or steel and NOA materials n Semimetallic materials—A higher quantity of steel, copper, and/or brass

wners of high-performance cars, however, may consider O fade resistance and stopping power at high speeds more important than noise levels or wear rate. The Society of Automotive Engineers (SAE) has a dopted letter codes to rate brake lining materials’ coeffi cient of friction. The rating is written on the edge of the friction linings and is called the edge code FIGURE 32-21 . The lower the letter, the less friction the material has, and the harder the brake pedal must be applied to achieve a given amount of stopping power. These code letters represent the following coeffi cients of friction: n C: ≤ 0.15 n D: 0.15–0.25 n E: 0.25–0.35 n F: 0.35–0.45 n G: 0.045–0.55 n H: > 0.55 n Z: Unclassifi ed The lining is tested both cool and hot. The rating is a two letter designation such as “FF.” The first letter is for the cool performance and the second letter is

section vi BrakeS

FIGURE 32-21 32-21 Brake lining edge code.

FIGURE 32-22 32-22 Brake pad shims and guides.

for the hot performance. For example, FF has a cool coeffi cient of friction of 0.35–0.45 and the same coeffi cient of friction at the hot temperature. It also is very possible that the hot and cold ratings differ from each other. For example, if the rating is FE, the coeffi cient of friction reduces as the temperature of the lining heats up. Notice that the coeffi cient of friction range is quite wide for each letter designation. Linings with the same letter ratings may not have the same braking performance as each other. This means that an EE-rated lining from one manufacturer is likely to have different braking characteristics than an EE-rated lining from another manufacturer. Always use high-quality brake lining from reliable companies to help avoid brake issues.

Anti-Noise Measures

isc brakes are more prone to annoying brake squealD ing than are drum brakes. Brake squealing is caused by vibrations set up between the brake pad and rotor. Manufacturers have addressed this problem in a number of ways: 1. Using softer linings with a higher coeffi cient of friction, which are less prone to noise than harder linings with a lower coeffi cient of friction 2. Adding brake pad shims and guides to the brake pads, which help cushion the brake pad and absorb some of the vibration FIGURE 32-22 3. Using springs to tightly hold the pads in place to minimize vibration FIGURE 32-23 4. Contouring and grooving the lining material in a way that minimizes vibration FIGURE 32-24

FIGURE 32-23 32-23 Example of brake pad retainers.

FIGURE 32-24 32-24 Brake lining grooves and contouring.

chapter 32 Disc Brake System

5. Incorporating bendable tangs on the brake pad backing plate that allow technicians to crimp the tangs so they are more fi rmly mounted in the caliper FIGURE 32-25

S ome manufacturers claim that reﬁ nishing their rotors removes enough material from the rotor that it can cause the brakes to squeal due to less mass, which changes the harmonic vibration qualities of the rotor. They recommend replacing the rotors any time the rotors are worn enough to need resurfacing.

TECHNICIAN TIP

Technicians also can apply noise-reducing compounds to the brake pads. One is a type of hightemperature liquid rubber compound that is applied to the back of the brake pad. When it cures, it stays fl exible and absorbs brake pad vibrations and helps reduce brake noise. Another compound is a specially designed liquid that is applied directly to the face of the lining material. This compound helps to modify the lining’s coeffi cient of friction slightly, making it less likely that the lining will squeal. Make sure you apply the correct compound to the correct side of the brake pad.

applied

Science

AS-36: Sound: The technician can demonstrate an understanding of the role sound plays in identifying various problems in the vehicle. Sound is a series of waves that travel through a gas, liquid, or solid and can often be heard by the human ear. Sound waves are created by vibrating objects, such as a guitar string. Moving objects that are in sliding contact with each other are highly likely to create sound. One example of this is fi ngernails dragging on a chalkboard. The fi ngernails vibrate on the surface of the chalkboard and create sound waves that are then heard by the ear. T echnicians commonly use differences in sound to assist in diagnosing disc brake problems. For example, brake pads that are worn down to the metal backing plate make a deep grinding noise when the brakes are applied. Listening to hear which wheel or wheels the noise is coming from helps identify the source of the problem. In the same way, if the disc brakes are equipped with a scratcher style of brake warning system, the brakes will make a high-pitched screeching noise. Many times this noise will happen when the vehicle is being driven when the brakes are not applied. One way to help determine which side the noise is coming from is by driving the vehicle next to a concrete traffi c wall or building. If the noise is on that side, it will get much louder than when not near the wall.

FIGURE 32-25 32-25 Brake pad bendable tangs.

Wear indicators

S ome manufacturers provide a means of notifying the driver that the brake pad linings are worn to their minimum limit. This helps ensure that the brake linings do not wear down to the point that they cannot properly perform their job anymore. Excessively thin brake linings tend to heat up quicker than thicker linings, which can lead to premature brake fade. Not all manufacturers use a brake lining wear indicator. In those cases, it is especially Applied Math, Science, and important to inspect the brakes at regular intervals, usuCommunication boxes identify ally during tire rotations or oil changes. critical academic concepts that the student must master.

Types These boxes show how to apply

abstract concepts directly to S ome manufacturers use a mechanically operated wear everyday activities in the shop. indicator to notify the driver that the brake pads are worn to their minimum limit. This is achieved by a spring mounted to the brake pad FIGURE 32-26 . steel scratcher mounted to the brake pad Part of the scratcher extends below the brake pad backing plate at the lining’s minimum wear thickness. When the friction material wears down far enough, the scratcher contacts the surface of the rotor and makes a squealing noise similar to fi ngernails on a chalkboard. This distinctive noise means the brakes need service right away. When you replace the brake pads, make sure they come

TECHNICIAN TIP I n many cases, the scratchers will start to make noise when the brakes are not applied and stop making noise when the brakes are applied, as applying the brakes tends to dampen the vibrations.

section vi BrakeS

made of reinforced carbon, carbon ceramic, or composite ceramic substances to reduce weight and withstand much higher temperatures. Since the rotor surfaces are squeezed between two brake pads, any unevenness of the rotor surfaces will cause pulsation of the brakes as the thicker and thinner portions pass between the brake pads. The rotor surfaces must be parallel to each other to avoid this situation. Rotors can fail in two ways: parallelism, which is also called thickness variation, and lateral runout. Parallelism is the most critical condition. If the rotor’s thickness varies by as little a 0.003" (0.076 mm), the rotor will tend to push the brake pads outward at any high spots. This tends to create more pressure on the brake pads and slows the vehicle down faster at that point. It also pushes up on the brake pedal as fl uid is being forced back to the master cylinder. The result is a pulsation of the brake pedal and a surging of the vehicle while braking, which is usually more noticeable at lower braking speeds. Lateral runout , also called warpage, is the side- toside movement of the rotor surfaces as the rotor turns. A warped rotor can be within specifi cations for parallelism but out of specifi cation for lateral runout. Lateral runout tends to move the caliper pistons in the same direction as each other, so brake fl uid is not pushed back to the master cylinder. However, the caliper tends to be moved side to side. This movement can cause the steering wheel to shimmy as the warped rotor follows the brake pads, if the lateral runout is greater than about 0.003" (0.076 mm). Also, runout causes the pads to rub on high spots of the rotor when the brakes are not being applied, causing uneven wear and/or the depositing of pad material on the rotor, which leads to thickness variation concerns.

FIGURE 32-26 32-26 The scratcher brake wear indicator.

equipped with new scratchers set to the correct depth so they can function the next time the pads wear down. Some manufacturers use a warning lamp or warning message on the dash to alert the driver that the lining is worn to its minimum thickness. These systems have an electrical contact installed on the brake pad at the point of the lining’s minimum wear thickness. When the pad wears to this minimum thickness, the contact touches the rotor as the brakes are applied, prompting a warning light or warning message that tells the driver the disc brake pads are due for replacement. These contacts can be manufactured into the pad or they can be clipped onto the pad. The contacts are normally replaced when the pads are replaced. Make sure that either the contacts come with the new pads or order them along with the pads.

Disc Brake Rotors

he brake disc or rotor is the main rotating component T of the disc brake unit. The wheel is bolted to the rotor and they rotate together, leading some manufacturers to integrate the anti-lock brake system (ABS) tone wheel Technician Tips provide realinto the rotor. Since friction between the rotor and brake world advice from experienced pads generates great amounts of heat, rotors must be able automotive technicians. to withstand high temperatures. The pads are also forced onto the surface of the rotor with potentially thousands of pounds of force, so the rotor must be strong and have a durable surface. The rotors are usually made of cast iron. To reduce weight, some manufacturers use a twopart rotor with a cast iron disc and a stamped steel center hat. This style of rotor is called a composite rotor. Some heavy-duty and/or high-performance vehicles have rotors

TECHNICIAN TIP

otors can be warped by improperly torquing the lug r nuts. always use a properly calibrated torque wrench (or the proper torque stick if the shop policy allows) to torque the lug nuts to the manufacturer’s speciﬁ ed torque.

or proper operation, rotors must maintain their F shape and resist warpage under high heat and pressure conditions. Because of these requirements, they are usually made of cast iron. On motorcycles, rotors are often made of stainless steel for cosmetic reasons. Disc brakes also are equipped with a dust shield to help protect the rotor. Dust shields help keep dust, water, and other road debris away from the inside surface of the rotor. They also

chapter 32 Disc Brake System

can help direct air fl ow to the rotor to assist with heat transfer to the atmosphere. Dust shields are commonly made of stamped sheet metal, but they also can be made of plastic. Dust shields can become damaged during brake repair so always inspect them for proper clearance before installing the wheel assembly. B

otors can be solid or ventilated FIGURE 32-27 . Solid R rotors are less expensive and usually found on smaller vehicles. Ventilated rotors are used to improve heat transfer to the atmosphere. These passageways are designed to use centrifugal force to cause air to fl ow through the center of the rotor when it is rotating. Ventilated rotors are used on heavier vehicles or high-performance vehicles. Some ventilated rotors are directional, meaning they are designed to force air through the rotor in one direction only FIGURE 32-28 . If the rotor is rotated in the wrong direction, it will not pump air properly and will overheat easier.

Types of Rotors

FIGURE 32-27 32-27 A. Standard rotors. B. Ventilated rotors.

isc brake rotors with holes or slots machined into D their surface dissipate heat quicker FIGURE 32-29 . They also help to remove water quickly from the surface of the pad in wet driving conditions. Since the pads wipe across the holes or slots, the surface of the pad is prevented from becoming hard and glassy smooth from the friction and heat of use. However, this scraping action reduces the overall life of the brake pad, so these types of rotors are generally only used in high-performance or race vehicles. Most disc brake rotors are stamped with the manufacturer’s minimum thickness specifi cation FIGURE 32-30 . This minimum thickness ensures an adequate amount of thermal mass for stopping power FIGURE 32-31 . When material is removed, there is not as much material to absorb heat and the rotor heats up faster. The excess heat can lead to brake fade sooner. Also, when the brake pads wear, if the thickness of the rotor were below this minimum, the piston could be pushed out beyond the edge of the sealing ring, which would cause the brakes to lose hydraulic pressure and fail. Make sure the rotors are always above the manufacturer’s minimum thickness before putting them back in service.

Direction of

I f you hear a loud scraping or grinding noise when you test-drive a vehicle after servicing the brakes, check to see if the dust shield is contacting one of the rotors. If so, it can make a lot of loud grinding noises. Since it is thin sheet metal, chances are good that it is bent. It can usually be bent back into shape easily.

rot ati o

TECHNICIAN TIP

FIGURE 32-28 32-28 Directional ventilated rotor.

FIGURE 32-29 32-29 Slotted and drilled rotor.

section vi BrakeS

used on some vehicles. The electric motor can pull on a conventional parking brake cable, or the electric motor can be mounted on the caliper and directly drive the caliper piston to apply force to the brake pads.

Integrated Mechanical Parking Brake Calipers

FIGURE 32-30 32-30 Rotor with minimum thickness stamped on it.

he integrated parking brake mechanically forces the disc T brake piston outward, forcing the brake pads to clamp the rotor when the parking brake is applied FIGURE 32-32 . A lever on the back side of the caliper is pulled by the parking brake cable. The lever converts that motion to rotary motion on a shaft that enters the rear of the caliper cylinder. The shaft uses a seal to prevent fl uid leakage from the bore. The shaft has a coarse thread machined into it, which threads into a nut assembly inside the caliper piston. As the shaft is turned by the parking brake lever, the nut causes the piston to be forced outward, applying the brakes. Releasing the parking brake cable allows a spring to unwind the shaft and release the pressure on the brake pads.

Top Hat Design Parking Brake

400° F

Rotor-Standard Thickness (At end of moderate hill)

500° F

Rotor-Below Minimum Thickness (At end of moderate hill)

FIGURE 32-31 32-31 Rotor thickness and heat capacity.

Parking Brakes

arking brakes are designed to hold the vehicle stationary P when parked. Manufacturers are required to design the vehicle so the parking brake will hold the vehicle for a given amount of time on a specifi ed grade in both directions. The parking brake must be separately activated from the service brakes, and the driver must be able to latch it into the applied position. Parking brakes can be foot operated or hand operated. Since disc brakes require higher applied forces to operate, they are a bit more diffi cult to use as parking brakes. However, manufacturers have overcome this challenge in a couple of ways.

he top hat design gets it name from the shape of the T rotor. The rotor has a deeper offset than normal, giving the appearance of a top hat. The offset portion allows room for a drum surface within the center of the rotor. Drum brake shoes are mechanically forced outward into contact with the inside of the brake drum, which locks the wheel. Releasing the parking brake allows the springs to retract the brake shoes from contact with the drums.

Electric Parking Brake

he electric parking brake uses an electric motor to T apply the disc brake assemblies. The cable style uses an electric motor to pull standard parking brake cables, which apply standard integrated mechanical parking brake calipers. The electrically integrated caliper style

Types of Parking Brakes urrently most parking brakes are mechanically applied C by use of a cable and ratcheting lever assembly. Parking brakes on disc brake units are primarily of two types: an integrated parking brake caliper and the top hat drum style. Alternatively, electric parking brakes are being

FIGURE 32-32 32-32 Integrated parking brake operation.

chapter 32 Disc Brake System

is illuminated, the ABS system is deactivated, and you should not try to activate ABS on a test drive. If the yellow ABS lamp is off, the ABS system should be active and ready to activate. It is helpful when testing ABS to do so on a surface with limited traction, such as wet pavement or a dirt road. When you do apply the brakes fi rmly, ABS activation can typically be felt as pulsations in the brake pedal and possibly the steering wheel. The vehicle should brake quickly while maintaining steering control. In some cases, a “poor traction” lamp may illuminate, telling you that the ABS system had to activate. This warning lamp will usually turn off after several seconds. If the yellow ABS warning lamp illumines, it typically means that the vehicle’s PCM has observed a fault in the ABS system and will need to be checked for DTCs. Once the customer concern has been verifi ed, you will hopefully have enough information to know how best to proceed. This could be as simple as performing a visual i nspection of the brake fl uid level and condition, removing the wheels to disassemble and inspect the brake units, looking up technical service bulletins, or reviewing the diagnostic troubleshooting chart for the particular sympCurrent state-of-the-art tom in the service information to determine the next step. automotive technology content Suspension and steering system faults can appear to is presented in an engaging and be brake system faults. An example of this is a pulling comprehensive writing style. condition while braking. If the strut rod bushings on the Throughout the text, the student suspension are worn, then braking the vehicle will cause is reminded how the knowledge the wheel to move rearward; at the same time, that will will be applied in the shop. cause the steering angle to change, causing the wheel to point in a direction other than straight down the road, imitating a brake pull. The braking system on a vehicle must be restored to its proper operation. Diagnosis of any problem must identify all issues that would prevent the brakes from operating normally. Lawyers and technicians have been known to say, “He who touched the brake system last, owns it!” What this means is that if there is a problem in the brake system and you inspected it or worked on it, you are very likely liable for anything that went wrong with it. Brake system failures are more likely to lead to vehicle accidents than failures of most systems. Any diagnosis and subsequent repairs need to be thorough and complete.

uses an electric motor mounted on the caliper to directly apply the brakes. Pushing a parking brake button on the dash causes the motor to either tension the cable or directly apply the parking brake. Electric parking brakes also can be integrated with the controller area network bus ( CAN-bus) system to provide additional features beyond just holding the vehicle when it is parked. It can be used to automatically hold the vehicle while it is stopped on a hill to prevent it from rolling backward or forward. It also can be automatically released by the vehicle’s e lectronic control module (ECM) when the throttle is applied for starting to move away from the stop. It also may work with the vehicle’s proximity detector when backing up. If the system detects the vehicle getting too close to an object, the ECM can apply the electric parking brake to stop the vehicle and prevent it from striking the object.

Diagnosis

isc brake diagnosis usually starts with understanding D the customer’s concern. Communicating directly with the customer is the best way to do that, but the customer is not always available. An experienced service advisor will gather the required information, so you should read the service advisor’s notes on the repair order carefully or speak with him or her directly. Once you understand the customer’s concern, a test-drive is usually needed to verify the accuracy of the concern. This is a good opportunity to test the brakes under a variety of conditions. Replicating the customer concern is important in order to address the situation that the customer is experiencing. During the test-drive, fi nd a safe place to operate the brakes at a variety of speeds with a variety of brake pedal pressures, especially trying to mimic the conditions the customer described. It is may be necessary to go on a test drive with the customer driving, allowing him or her to operate the vehicle in the way that makes the problem evident and point out the particular situation he or she is experiencing. Also, it is good to have the customer along in case the problem does not occur, in which case he or she won’t think you don’t believe them or are ignoring the issue. If there is a concern related to the anti-lock brake system (ABS) that requires a test drive, extreme caution is required so that an accident doesn’t happen. Since ABS operates only during extreme braking or poor traction conditions, you run the risk of being rear-ended by a vehicle behind you or losing control of the vehicle if you apply the brakes hard enough to activate the ABS. So make sure the vehicle is being tested away from all other traffi c. Remember that if the yellow ABS warning lamp

TECHNICIAN TIP ne way to help identify if a problem is coming from O the front or rear brakes is to test-drive the vehicle in a safe place at a relatively low speed and lightly apply the parking brake. If the condition is still present, the problem is with the rear brakes, since the parking brakes are usually on the rear wheels. If the condition is not present, the problem is likely with the front brakes.

section vi BrakeS

Removing and Inspecting Calipers emoving the caliper is necessary for replacing the brake R pads on most vehicles. It also allows access for machining

The tools that are used to diagnose and repair brake systems include: n Brake lining thickness gauges —Used to measure the thickness of the brake lining n Brake wash station —Used to clean drum and disc brake dust n C aliper piston pliers —Used to grip caliper pistons when removing them n D isc brake rotor micrometer —Used to measure the thickness and parallelism of a rotor n D ial indicator —Used to measure the lateral runout (side to side) of the rotor n P arking brake cable pliers —Used to install parking brake cables n C aliper piston retracting tool —Used to retract caliper pistons with integrated parking brakes n C -clamp —Used to push pistons back into the caliper bore on non-integrated parking brakes n O ff-car brake lathe —Used to machine drums and rotors that are off the vehicle n O n-car brake lathe —Used to machine rotors that are on the vehicle n C aliper dust boot seal driver set —Consists of a driver and a variety of adapters used to install various sizes of dust boot seals FIGURE 32-33

system and the manufacturer’s diagnostic procedure for the condition. Perform any diagnostic tests to identify the cause of the condition. This could be a visual inspection or any other prescribed test, such as a power booster test. It could also involve a detailed testing sequence, such as testing the proportioning and metering valves. Once you have identifi ed the cause of the fault, determine the action that will rectify the fault.

Tools

TABLE 32-2: Common Brake Issues Concern

Fault

Poor stopping

• Power booster not operating properly • Internal master cylinder leak; air in the hydraulic system • Metering valve or proportioning valve blocking ﬂ uid ﬂ ow • Improperly adjusted drum brakes • Improper friction lining material • Contaminated linings

Noise

• • • •

Vibration

• Improper friction lining material • rotor surface ﬁ nish not correct • Foreign object (mud, rocks, etc.) in the rotor • Warped rotor • aBS operating

Pulling

• • • • • •

Plugged or restricted brake hose Stuck caliper piston Seized caliper guide pins Contaminated lining Lining worn down to metal air in the hydraulic system

Grabbing

• • • •

Contaminated lining Stuck caliper piston Internal master cylinder leak Misadjusted drum brakes

Dragging

• Stuck caliper piston • Seized caliper guide pins • Misadjusted master cylinder pushrod length • Binding brake pedal • Plugged or restricted brake line or hose

Pulsation

• Warped rotors • rotor parallelism • aBS operation

Diagnosing Disc Brakes

o diagnose poor stopping, noise, vibration, pulling, T grabbing, dragging, or pulsation concerns and determine any necessary actions, follow the steps outlined in the Tables organize information so remainder of this chapter. While braking concerns are students can quickly locate and generally easier to diagnose than most of the other sysretain critical information. tems on the vehicle, the large variety of conditions listed makes it imperative that you have a good understanding of disc brake and hydraulic theory. It also helps to use all of your senses to assist you in identifying the location of the fault. As a reminder, TABLE 32-2 lists some of the common faults to consider for each concern. Verify the customer concern by operating the vehicle if safe to do so. Depending on the concern, it may be as simple as stepping on the brake pedal without moving the vehicle and feeling the pedal sink to the fl oor, or it could require a more detailed test-drive to observe the fault the customer is describing. Regardless of the condition, it is almost always good practice to research any technical service bulletins (TSBs) for the particular situation. If no related TSBs are found, research the service information to familiarize yourself with the

Friction lining material too hard Lining worn down to metal Worn caliper slides/guide pins Component-speciﬁ c noises

chapter 32 Disc Brake System

ÂŠ SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

FIGURE 32-33 32-33 A. Brake lining thickness gauges. B. Brake wash station. C. Caliper piston pliers. D. Disc brake rotor micrometer. E. Dial indicator. F. Parking brake cable tool. G. Caliper piston retracting tool. H. Off-car brake lathe. I. On-car brake lathe. J. Caliper dust boot seal driver set.

section vi BrakeS

of the rotors on the vehicle, removal of the rotors for removed, you might want to use a brake pedal replacement, or machining of the rotors off the vehicle. holding tool to slightly apply the brakes and block Further, it allows for a thorough inspection of the caliper, off the compensating ports in the master cylinder. pads, and rotor to determine the cause of a brake conJust remember that the brake lights will stay on if cern. To remove the caliper assembly, inspect for leaks you don’t pull the brake light fuse. (Step 3) and damage to the caliper housing, and determine any 5 Remove the brake line or hose from the caliper. Be necessary actions, follow the steps in SKILL SKILL DrILL 32-1 : careful not to lose the two brake hose copper (or Research the procedure for removing the caliper aluminum) sealing rings, if equipped. (Step 4) 1 in the appropriate service information. Follow 6 Push the caliper pistons back into their bores this procedure. The following steps are general slightly. Use of a small pry bar or C-clamp will in nature and should not be substituted for the usually force the piston back just far enough so anufacturer’s specifi c procedure. m that the caliper can be removed from the pads and rotor once the caliper is loose from its mount. 2 If the caliper is likely to be reinstalled on the vehicle or rebuilt and reinstalled, it is good practice (Step 5) to loosen the bleeder screws slightly and then 7 Remove the caliper assembly from its mountings, retighten them. Doing so ensures that they are following the service manual procedure. Be careful not seized in place and that they will be able to be to avoid dislodging brake dust, which may contain l oosened later when bleeding the system. Failure to asbestos. (Step 6) do this now could waste a lot of time later trying to 8 Inspect the caliper for leaks or damage, including 1) repair a bleeder screw when it breaks off. (Step 1) the piston dust boot. If the caliper is being rebuilt or a new caliper will Determine any necessary actions. (Step 7) Determine any necessary actions. “Know-See-Do-Prove” The icon is tied to CDX’s unique and be installed, it is good practice to fl ush the old proven instructional methodology. The color-coding within the brake fl uid from the system at this time, so that old icon is designed to act as a roadmap. Green represents Know brake fl uid will not have to be bled through the and indicates where basic principles and concepts are presented. new or newly rebuilt caliper. Also, leave the masRed represents See and indicates where skills are presented. Blue ter cylinder reservoir level low so that pushing the represents Do, and indicates that practical skill-building exercises Some technicians pinch off the ﬂ exible brake hoses caliper pistons into their bores will not overfl ow with vice grip pliers. This should be avoided because it and tasksheets are available for students in the associated tasksheet the reservoir. (Step 2) crimps the hose, potentially damaging it internally and/ manual. Purple represents Prove, and indicates where To minimize the amount of brake fl uid d raining or externally. students can assess what they have learned. out of the brake lines or hoses when they are

SKILL DRILL

Research the procedure for

removing the caliper in the

Removing and Inspecting Calipers

32-1

appropriate service information. Loosen the bleeder screws slightly and then retighten them.

If the caliper is being rebuilt or

a new caliper will be installed, it is good practice to flush the old brake fluid from the system at this time.

Use a brake pedal holding tool to

slightly apply the brakes and block off the compensating ports in the master cylinder to avoid excess fluid leakage.

chapter 32 Disc Brake System

32-1 Removing and Inspecting Calipers, continued

SKILL DRILL

Remove the brake line or hose from the caliper. Be careful not to lose the sealing rings.

damage, including the piston dust

Push the caliper pistons back into their bores slightly.

Remove the caliper assembly from its mountings.

Inspect the caliper for leaks or

boot. Determine any necessary actions.

Inspecting Caliper Mountings, Slides, and Pins

he caliper mountings and slides/pins are placed under T heavy loads and forces. They also operate in harsh environments. It is common that they experience wear over time. They can also corrode and bind up. Clean caliper mountings and slides/pins thoroughly, and inspect them closely. To clean and inspect caliper mountings and slides/ pins for operation, wear, and damage and to determine any necessary actions, follow the steps in SKILL SKILL DrILL 32-2 : Clean the caliper mountings and slides/pins using 1 equipment/procedures for dealing with asbestos/ hazardous dust. Once the dust is taken care of, you

may need to use a brake cleaning solvent to clean the components further. (Step 1) Inspect the caliper mountings and slides/pins for signs of wear and damage. Also look for stripped threads on the pins or caliper. Determine any necessary actions. (Step 2)

Inspecting Brake Pads and Wear Indicators he wear indicator system could be a scratcher type or T a sensor type. It is also very possible that the vehicle does not incorporate any type of wear indicator system. Checking this system usually consists of verifying that the sensor or scratcher is not contacting or nearly contacting

section vi BrakeS

the brake rotor. Some manufacturers require that the s ensor be grounded with a test lead and that the brake pad warning lamp or warning message come on. o check the operation of the brake pad wear T indicator system and determine any necessary actions, SKILL DrILL 32-3 : follow the steps in SKILL

Research the service information to determine the type of wear indicator system utilized and the rocedure to test it. p Check that it is not contacting or nearly contact ing the rotor. It is also good practice to measure the brake pad lining thickness and compare it to

32-2 Inspecting Caliper Mountings, Slides, and Pins

SKILL DRILL

Clean the caliper mountings and slides/pins using equipment/ procedures for dealing with asbestos/hazardous dust.

SKILL DRILL

32-3

Determine the type of wear

indicator system utilized. Check

that it is not contacting or nearly contacting the rotor.

Inspect the caliper mountings and slides/pins for wear and damage. Determine any necessary actions.

Inspecting Brake Pads and Wear Indicators

If the system is a sensor style,

test the system to verify that the

system is operational. Determine any necessary actions.

chapter 32 Disc Brake System

Checking Brake Pads

Disassembling Calipers alipers are disassembled and cleaned for a couple of C reasons. The fi rst is to diagnose a brake system concern related to one or more calipers. For example, if the vehicle has a brake pull, it could be caused by a sticking caliper piston. Disassembling the caliper will allow you to verify whether that is the case or not. They also need to be disassembled and cleaned if they are going to be rebuilt. Some shops rebuild the calipers themselves, but most shops just replace them with rebuilt calipers if necessary. Disc brake calipers are usually side specifi c, meaning they are designed to be installed on a particular side of the vehicle. Failure to install them on the correct side usually results in the bleeder screws being on the bottom of the caliper cylinder. This will prevent air from being bled from the caliper and result in a very spongy brake pedal.

emoving the brake pads is the most thorough way to R inspect the brake pads. During a routine maintenance inspection where there are no customer concerns regarding the brakes, a simple measurement of the lining thickness is usually adequate. But if there are customer concerns with the brakes, it may be necessary to remove the pads for a more detailed inspection. This could show cracks in the lining or other defects that wouldn’t be otherwise seen from the outside. It also allows for a more thorough inspection of the retaining hardware. Also pay attention to the way the brake pads come off, as some pads have slight differences (such as locating nipples) that make it easy to install them incorrectly. To remove, inspect, and replace pads and retaining hardware and to determine any necessary actions, follow the steps in SKILL SKILL DrILL 32-4 : Remove the pads and retaining hardware. If 1 necessary, clean the parts with the appropriate equipment or cleaner. Inspect all pads, retaining hardware, and anti-noise 2 shims for wear or damage. Problems could include cracked linings and worn or missing retaining hardware or shims. (Step 1)

Measure the remaining brake pad thickness and compare to specifi cations. Inspect the pads to see if they are wearing evenly. If not, it could indicate a caliper or caliper mounting issue. Determine any necessary actions. (Step 2)

the manufacturer’s minimum specifi cations. If the brake pads are near the end of their useful life, it would be good practice to inform the customer and recommend replacement of the pads. (Step 1) If the system is a sensor style, test the system to verify that the system is operational. Determine any necessary actions. (Step 2)

SKILL DRILL

TECHNICIAN TIP

ecause you have the rotor exposed, skip ahead to B the sections on inspecting and servicing rotors, and complete the tasks listed there. This will save you time and effort. Pick up here once you are done with the rotor.

32-4 Checking Brake Pads

Remove the pads and retaining

hardware. Inspect all pads,

retaining hardware, and anti-noise shims for wear or damage.

Measure the remaining brake pad

thickness and compare to specifi-

cations. Determine any necessary action(s).

section vi BrakeS

SKILL DRILL

Reassembling Calipers

pick tools, such as dental picks, and then wiping out the groove with a rag. (Step 2) Inspect each of the parts for damage, rust, and wear. Also check the caliper pin bores or bushings for wear or damage. (Step 3) Measure the caliper bore-to-piston clearance with a feeler gauge and compare to specifi cations, if available. Determine any necessary actions. (Step 4)

eassembling the caliper requires patience and attention R to detail. Ensure that the sealing ring groove is spotless and that the O-ring gets seated fully in the groove. Use

o disassemble and clean the caliper assembly; T inspect parts for wear, rust, scoring, and damage; and replace the seal, boot, and damaged or worn parts, follow the steps in SKILL SKILL DrILL 32-5 : 1 Disassemble the caliper, following the service manual procedure. If this involves using compressed air to remove the piston, be very careful, as the piston can pop out with great force, enough to break fi nger bones or pinch fi ngers off. Always use an approved cushion between the caliper piston and caliper housing. Keep your fi ngers away from the area. (Step 1) 2 Clean all of the caliper parts according to the service manual procedure. Make sure the sealing ring groove is completely clean. This can be performed by scraping the groove with a variety of

32-5 Disassembling Calipers

Disassemble the caliper, following

the service manual procedure.

Clean all of the caliper parts

following the service manual procedure.

Inspect each of the parts for

damage, rust, and wear.

Skill Drills provide written stepby-step explanations and visual summaries of important skills and procedures. This format enhances student comprehension of complex procedures.

Measure the caliper bore-to-piston clearance with a feeler gauge and compare to specifications. Determine any necessary actions.

CHAPTER 32 Disc Brake System

TECHNICIAN TIP

In some cases, the piston cannot be removed with compressed air due to the piston being seized in the bore. If this happens, reinstall the calipers on the vehicle without the pads, bleed the brakes, and use the brake pedal to force the stuck piston out of the caliper. You may have to block any nonseized pistons so they don’t pop out; that way, just the seized piston gets pushed out.

Reassemble the caliper assembly, following the manufacturer’s procedure. Lubricate the sealing

clean brake fluid or approved caliper piston assembly lube on the piston and sealing ring prior to installing it. Also check the service manual to see when the piston dust boot needs to be installed. Some calipers require the dust boot to be installed in the caliper before installing the piston. In this case, a special technique using air pressure to “balloon” the dust boot is required so the piston can slip inside it. Ask your supervisor to demonstrate this technique. To reassemble, lubricate, and reinstall the caliper, pads, and related hardware; seat pads; and inspect for leaks, follow the steps in SKILL DRILL 32-6 : 1 Make sure the rotor has been properly installed on the hub/spindle and that the hub mating surface is free of rust or dirt. (Step 1)

SKILL DRILL

32-6

Reassembling Calipers

Make sure the rotor has been properly installed on the hub/ spindle and the hub surface is free of rust or dirt.

Reassemble the caliper assembly, following the manufacturer’s procedure.

Assemble the pads, hardware, and caliper on the caliper mountings using the specified lubricant.

Reinstall the brake line fittings using two new copper washers (if equipped).

Tighten the brake line fitting and caliper bolts to the proper torque. Bleed the brakes following the manufacturer’s procedure.

Seat the pads by applying the brake pedal several times, not allowing the pedal to go all the way to the floor.

SECTION VI BRAKES

32-6

Reassembling Calipers, continued

ÂŠ SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

SKILL DRILL

5 6

If the brake pedal is spongy, you will need to bleed the brakes of any remaining trapped air in the system.

Inspect the system for any brake fluid leaks, no matter how small.

ring, piston, and any other moving parts. Be careful to not pinch, twist, or cut the sealing ring and dust boot. (Step 2) Assemble the pads, hardware, and caliper on the caliper mountings using the specified lubricant. (Step 3) Reinstall the brake line fittings using two new copper washers (if equipped). Place one between the brake line fitting and the head of the banjo bolt and the other between the brake line fitting and the caliper. (Step 4) Tighten the brake line fitting and the caliper mounting bolt(s) to the proper torque. Bleed the brakes following the manufacturerâ&#x20AC;&#x2122;s procedure. See the brake bleeding skill drills in the Hydraulics and Power Brakes chapter for more information. (Step 5) Seat the pads by applying the brake pedal several times. It is a good idea to place your left foot under the brake pedal so that when applying the pedal with your right foot, the pedal does not push the master cylinder pistons farther into the master cylinder bore, which could dislodge sludge or cut the lips of the master cylinder primary seals. Applying the brake will force the brake caliper pistons to adjust to the proper clearance for proper

brake application. You may need to start the vehicle to enable the power booster to help you fully apply the brakes, especially if the vehicle is equipped with integrated parking brake calipers. (Step 6) If the brake pedal is spongy, you will need to bleed the brakes of any remaining trapped air in the system. (Step 7) If the brake pedal is firm and does not sink over time, there could still be a small leak that would cause a future brake failure. Inspect the system for any brake fluid leaks, no matter how small; if found, inform your supervisor/instructor. (Step 8)

Retracting and Readjusting Pistons on an Integrated Parking Brake Retracting the caliper piston on an integrated parking brake system is different than on a standard caliper. Since the integrated parking brake system uses a threaded shaft to force the piston outward from the caliper bore, it cannot just be retracted with a C-clamp. The piston will need to be screwed back in on the threaded shaft to retract it into the bore. This is accomplished by using a tool that mates to slots, grooves, or holes in the outer face of the piston. The tool is then turned by hand or wrench to screw the piston back into the bore. Be careful to not tear the piston dust boot during this operation.

chapter 32 Disc Brake System

4 5

ratchet and tool need to be held tightly against the piston so it does not slip. There are other more application-specifi c tools that use the caliper housing to keep the tool from slipping out of the holes in the piston. This style works the best if you have access to one. (Step 1) Install the tool and turn it in the direction that causes the piston to retract. (Step 2) Continue turning until the piston is lightly seated at the bottom of its bore. (Step 3) Make sure the dust boot is seated properly in its grooves. (Step 4)

To retract the caliper piston on an integrated parking brake system, follow the steps in SKILL SKILL DrILL 32-7 : Research the procedure for retracting the caliper 1 piston on an integrated parking brake system in the appropriate service information, paying close attention to which direction the piston needs to be turned. Select the proper adapter or tool to match the 2 caliper piston. There are several types of tools that work. One is a multisided cube with a variety of projections of varying confi gurations on each side. This cube fi ts on the end of a ratchet. The

SKILL DRILL

Research the procedure for

retracting the caliper piston. Select the proper adapter or tool to match the caliper piston.

Make sure the dust boot is seated

properly in its grooves.

Retracting and Readjusting Pistons on an Integrated Parking Brake

32-7

Install the tool and turn it in the

direction that causes the piston to retract.

Continue turning until the piston is

lightly seated at the bottom of its bore.

section vi BrakeS

3 4 5

If you have not already done so, remove the caliper assembly, brake pads, and any hardware following the manufacturer’s procedure. Clean the rotor with approved asbestos removal equipment. (Step 1) Inspect the rotor for hard spots or hot spots, scoring, cracks, and damage. (Step 2) Measure the rotor thickness at the deepest groove or thinnest part of the rotor and compare to specifi cations. If it is under the allowed size, it will need to be replaced. If it needs to be machined and it is above the minimum thickness, check to see how badly it is scored. Remember that removing 0.015" (0.38 mm) on each side of the rotor results in the thickness being reduced by 0.030" (0.76 mm). Many rotors only start with 0.060" (1.52 mm) of machinable material when they are new. (Step 3) Measure the thickness of the rotor in a minimum of fi ve to eight places around face of the rotor. Calculate the maximum thickness variation by subtracting the minimum thickness from the maximum thickness and compare it to specifi cations. (Step 4)

he rotor thickness, lateral runout, and thickness T variation must be within specifications for the rotor to function properly. Rotors that are too thin cannot handle as much heat and will experience brake fade sooner than thicker rotors will. They also may cause the piston to be pushed out of the caliper bore far enough that the sealing ring no longer seals the piston. This would lead to a lack of braking action on at least half of the system. E xcessive thickness variation will cause brake pedal pulsation and the vehicle to have a surging feeling while coming to a stop. Excessive lateral runout tends to cause the steering wheel to shimmy. It also can cause an excessive thickness variation problem due to the high spot of the rotor continuously hitting the brake pad while driving down the road. This constant rubbing on the high spot of the rotor will wear it slightly, leading to excessive thickness variation across the face of the rotor. T o clean, inspect, and measure rotor thickness, lateral runout, and thickness variation and to determine any necessary action(s), follow the steps in SKILL SKILL DrILL 32-8 : Research the procedure and specifi cations for 1 i nspecting the rotor in the service information.

Inspecting and Measuring Disc Brake Rotors

SKILL DRILL

Inspecting and Measuring Disc Brake Rotors

32-8

Research the procedure and

specifications for inspecting the

rotor. If you have not already done so, remove the caliper assembly, brake pads, and any hardware. Clean the rotor with approved asbestos removal equipment.

Inspect the rotor for hard spots

or hot spots, scoring, cracks, and damage.

Measure the rotor thickness at the

deepest groove or thinnest part of the rotor.

chapter 32 Disc Brake System

32-8

Inspecting and Measuring Disc Brake Rotors, continued

SKILL DRILL

Measure the thickness of the

rotor in a minimum of five to

eight places around the face of the rotor. Calculate the maximum thickness variation.

Set up a dial indicator to measure

lateral runout. Rotate the rotor

and find the lowest spot on the rotor, then zero the dial indicator.

Slowly rotate the rotor to find

the highest spot on the rotor.

Read the dial indicator showing maximum runout.

Keep turning the rotor to make sure the dial indicator does not read below zero. If it does, rezero the dial caliper on the lowest spot. Keep turning the rotor to find the highest spot and reread the dial indicator. Compare all of your readings to the specifications and determine if the rotor is fit for service, is machinable, or needs to be replaced.

Set up a dial indicator to measure lateral runout. Rotate the rotor and fi nd the lowest spot on the rotor, then zero the dial indicator. (Step 5) Slowly rotate the rotor to fi nd the highest spot on the rotor. Read the dial indicator showing maximum runout. (Step 6)

section vi BrakeS

Removing and Reinstalling Rotors

emoving the rotor is usually required when the rotor R needs to be replaced because it is under the specifi ed minimum thickness or would be after machining. It also would need to be removed to be refi nished on an off-car brake lathe or to service the wheel bearings or axle shaft. Also, hubless rotors that are being machined with an on-car brake lathe need to be removed to clean off the rust and dirt accumulated between the rotor and the hub. otors are designed to be mounted in one of two R ways: hub style or hubless style. The hub style has the wheel bearing hub cast into the rotor. This style generally requires disassembly of the wheel bearing hub to remove the rotor from the vehicle. The hubless style uses a wheel bearing hub separate from the rotor, with the rotor held onto the hub by the wheel studs and lug nuts. Some hubs also use small screws to hold the rotor on the hub whenever the wheel is removed from the vehicle. Removing hubless rotors is generally easier than removing hub-style rotors, although some manufacturers design their rotors to unbolt from the rear side of the bearing hub. In these applications, the wheel bearing hub must be removed before the rotor can be removed from the hub.

To remove and reinstall the rotor, follow the steps in SKILL DrILL 32-9 : 1 Research the procedure for removing and reinstall ing the brake rotor in the appropriate service information. 2 If you have not already done so, remove the caliper assembly, brake pads, and any hardware, following the manufacturer’s procedure. 3 If the caliper mount straddles the rotor, remove it according to the specifi ed procedure. This is usually accomplished by removing bolts behind the rotor. (Step 1) , fi rst mark 4 To remove the hubless-style rotor the rotor for reinstallation in the correct position. A permanent marker, crayon, or center punch can be used to do this. (Step 2) 5 If there are screws or speed nuts holding the rotor to the hub, remove them following the specifi ed manufacturer procedure. (Step 3) 6 Remove the rotor from the hub. (Step 4) 7 To remove the hub-style rotor , remove the wheel bearing locking mechanism (cotter pin, lock nut, or peened washer). (Step 5) 8 Remove the wheel bearing adjusting nut, thrust washer, and outer bearing. (Step 6) 9 If the rear bearing must be removed for service or replacement of the rotor, use the following procedure to remove the inner bearing and grease seal.

Compare all of your readings to the specifi cations, and determine if the rotor is fi t for service, is machinable, or needs to be replaced. (Step 7)

SKILL DRILL

32-9

Research the procedure for

removing and reinstalling the

brake rotor. If you have not already done so, remove the caliper assembly, brake pads, and any hardware. If the caliper mount straddles the rotor, remove it.

Removing and Reinstalling Rotors

To remove the hubless-style

rotor, mark the rotor for proper reinstallation.

If there are screws or speed nuts

holding the rotor to the hub, remove them.

chapter 32 Disc Brake System

32-9

Removing and Reinstalling Rotors, continued

SKILL DRILL

Remove the rotor from the hub.

To remove the hub-style

rotor, remove the wheel bearing

locking mechanism.

Follow the steps of the inner

bearing and grease seal removal

procedure if the rear bearing must be removed.

If the rotor uses small screws to

10 hold the rotor to the hub, reinstall those and tighten to the proper torque.

To reinstall a hubless-style

rotor, clean all mounting surfaces

on the hub and rotor and remove any burrs.

Spin the rotor to ensure it spins

11 true and does not contact any other

components such as the dust shield.

Remove the wheel bearing adjust-

ing nut, thrust washer, and outer bearing.

Slip the rotor over the wheel

studs.

Be sure to properly lock the

12 adjustment nut in place once adjustment is completed.

section vi BrakeS

32-9

Removing and Reinstalling Rotors, continued

SKILL DRILL

Spin the rotor to ensure it spins

13 true and does not contact any other

components such as the dust shield.

n n n

n n

einstall the adjusting nut onto the spindle about R fi ve turns. Grasp the rotor on the top and bottom, and push it toward the center of the vehicle. Hold slight downward pressure as you fi rmly pull the rotor toward yourself. This should cause the adjusting nut to catch the wheel bearing and to pull it and the seal out of the rear of the hub. The grease seal will need to be replaced with a new one. Now would be a good time to perform any other rotor-related tasks such as inspecting and measuring a rotor, refi nishing a rotor, and servicing wheel bearings. Perform those tasks and return here to reinstall the rotor. If a new rotor is being installed, make sure to clean off any anticorrosion coating it was shipped with. Follow the rotor manufacturer’s procedure to remove this coating. (Step 7)

To reinstall a hubless-style rotor , fi rst clean all mounting surfaces on the hub and rotor and remove any burrs. (Step 8) 11 Slip the rotor over the wheel studs. (Step 9) If the rotor uses small screws to hold the rotor to 12 the hub, reinstall those and tighten to the proper torque. torque. (Step 10) Finally, spin the rotor to ensure it spins true and 13 does not contact any other components such as the dust shield. (Step 11) To reinstall a hub-style rotor , follow the wheel 14 bearing service skill drill in the Wheel Bearings 10

chapter to pack, install, and adjust the wheel bearings. bearings. (Step 12) 15 Be sure to properly lock the adjustment nut in place once the adjustment is completed. place once the adjustment is completed. (Step 13) 16 Finally, spin the rotor to ensure it spins true and does not contact any other components such as the dust shield. (Step 14)

Reﬁnishing Rotors on Vehicle

otors need to be refi nished when they have excessive R runout, thickness variation, or grooving. A brake lathe refi nishes the rotor surfaces by removing metal and truing the surfaces. If the grooving or surface defects are too great, the rotor may require the removal of too much metal to satisfactorily refi nish the surfaces. The rotor thickness should always be remeasured once the refi nishing is complete to ensure it is above the manufacturer’s minimum thickness. Rotors can be refi nished while on the vehicle or off the vehicle. On-vehicle refi nishing is preferred by most manufacturers (those who allow refinishing of their rotors) because it minimizes runout issues between the hub and rotor. Since the rotor is being machined as it is mounted on the vehicle, it is being refi nished true to the hub and other brake components. This minimizes any lateral runout issues. To refi nish a rotor while it is on the vehicle and to measure fi nal rotor thickness, follow the steps on SKILL SKILL DRILL 32-10 : 1 Research the brake lathe manufacturer’s procedure for properly refi nishing the rotor. Follow those guidelines completely.

chapter 32 Disc Brake System

overload the lathe, as well as make the rotors much thinner. (Step 4) 9 Install the anti-chatter device, if specifi ed. This will help give an acceptable fi nish on the rotor surfaces. 5) (Step 5) 10 Engage the automatic feed and watch for proper machining action. (Step 6) 11 If necessary, repeat this step until all damaged surface areas have been removed on both sides of the rotor. (Step 7) 12 If necessary, perform a fi nish cut on the rotor. Many newer machines use an elliptical motion to give a nondirectional fi nish, so a fi nish cut is not needed. 13 Remeasure the rotor thickness to determine if the rotor is above minimum thickness specifi cations. (Step 8) 14 If you had to adjust the wheel bearings in Step 3, readjust the bearings so they have the specifi ed end play or preload. (Step 9)

If working on a hubless-style rotor, remove the r otor and clean any dirt, rust, and debris from the mating surfaces of the rotor and hub. If working on a hub-style rotor, measure the wheel bearing end play. If excessive, adjust the bearings so there is no end play. Just remember to readjust them properly when the refi nishing process is complete. Mount the on-car brake lathe to the rotor. (Step 1) Perform the runout compensation on the brake lathe. Some brake lathes require manual compensation, while other machines can perform this as part of their features. Follow the lathe manufacturer’s procedure. (Step 2) Adjust the cutting bits and cut off any lip at the edge of the rotor. (Step 3) Make sure the cutting bits will not contact the rotor face, and move the cutting head toward the inner diameter of the rotor face. Set the cutting bits to the proper cutting depth for machining. This is usually between 0.004 and 0.015 of an inch. Too little removal tends to overheat the edge of the cutting bit. Too much can

SKILL DRILL

32-10

Research the brake lathe

manufacturer’s procedure for

properly refinishing the rotor. Mount the on-car brake lathe to the rotor after cleaning the rust and dirt from between the rotor and hub or adjusting the wheel bearing so there is no end play.

Reﬁnishing Rotors off Vehicle

Refi nishing a rotor while it is off the vehicle is a bit different than on-vehicle refi nishing. The major difference

Refinishing Hubless Rotors on Vehicle

Perform the runout calibration on

the brake lathe.

Adjust the cutting bits and cut off

any lip at the edge of the rotor.

section vi BrakeS

32-10

Refinishing Hubless Rotors on Vehicle, continued

SKILL DRILL

Make sure the cutting bits will not

contact the rotor face, and move

the cutting head toward the inner diameter of the rotor face. Set the cutting bits to the proper cutting depth for machining.

If necessary, perform a finish cut

on the rotor.

Install the anti-chatter device, if

specified.

Engage the automatic feed and

watch for proper machining

action. If necessary, repeat this step until all damaged surface areas have been removed on both sides of the rotor.

Remeasure the rotor thickness

to determine if the rotor is above

minimum thickness specifications.

is in the setup. Hub-style and hubless-style rotors each require their own way of being mounted on the brake lathe. Most hub-style rotors use the bearing races to drive and center the rotor on the lathe spindle. Thus, bearing adapters of the proper size need to be selected and used (see the Wheel Bearings chapter). The spindle nut then clamps the rotor onto the spindle through these bearing adapters and races. Hubless rotors are centered using a spring-loaded centering cone to align the rotor’s centering hole with the spindle. Clam shell clamps are then used on each side of the rotor to clamp it to the lathe spindle. Composite rotors use a special adapter which drives the rotor from the center hole and, at the same time, clamps it fi rmly between solid plates.

o refinish a rotor while it is off the vehicle and T measure final rotor thickness, follow the steps in SKILL DRILL 32-11 : 1 Research the brake lathe manufacturer’s procedure for properly refi nishing the rotor. Follow those guidelines completely. mounting 2 Clean nicks, burrs, or debris from the surfaces of the rotor including the centering hole, if used. Since the rotor is clamped to the lathe spindle, all of the surfaces on the rotor that contact the lathe components must be free of nicks, burrs, and rust; therefore, they must be cleaned prior to mounting the rotor on the lathe. This is especially true of a hubless-style rotor. (Step 1)

chapter 32 Disc Brake System 3 4

7 8 9

Set the cutting bits to the proper cutting depth for machining the ridge. (Step 5) By hand, move the cutting head outward toward the ridge. Slowly remove the ridge. (Step 6) Once the ridge is removed, run the cutting head all the way in to the inner face of the rotor. (Step 7) Set the cutting bits to the proper cutting depth for machining the rotor face. (Step 8)

SKILL DRILL

32-11

Research the brake lathe manu-

facturer’s procedure for properly

Refinishing Rotors off Vehicle

Position the cutting head about

one-quarter the way in from the outer diameter of the rotor.

Mount the rotor. Check that the

rotor is running true on the lathe.

cutting depth for machining the

refinishing the rotor. Clean nicks, burrs, or debris from the mounting surfaces of the rotor including the centering hole.

Mount the rotor onto the lathe. Check that the rotor is running true on the lathe. (Step 2) Install the anti-chatter band or anti-chatter pucks on the rotor. (Step 3) Make sure the cutting bits will not contact the rotor face, and move the cutting head in about one-quarter the way from the outer diameter of the rotor face. Turn on the lathe. (Step 4)

Set the cutting bits to the proper ridge.

Install the anti-chatter band or

anti-chatter pucks on the rotor.

outward toward the ridge. Slowly

By hand, move the cutting head remove the ridge.

section vi BrakeS

Engage the automatic feed on “fast” cut and watch for proper machining action. Some machines are called a “single-cut” or “single-pass” lathe and offer only one cutting speed. (Step 9) 11 If necessary, repeat Step 10 until all damaged surface areas have been removed on both sides of the rotor. 12 If necessary, perform a fi nish cut on the rotor. This is usually done on “slow” speed. (Step 10)

Use sandpaper or a drill with a sanding pad to give the rotor faces a nondirectional fi nish. (Step 11) 14 Remeasure the rotor thickness to determine if the rotor is above minimum thickness specifi cations. (Step 12) 15 Wash the machined rotor in a hot soapy water solution or parts washing cabinet to remove any metal particles, and dry. (Step 13) 13

32-11

Refinishing Rotors off Vehicle, continued

SKILL DRILL

Once the ridge is removed, run

the cutting head all the way in to the inner face of the rotor.

If necessary, perform a finish cut

10 on the rotor. This is usually done on “slow” speed.

Set the cutting bits to the proper

cutting depth for machining the rotor face.

Remeasure the rotor thick-

11 ness to determine if the rotor is above minimum thickness specifications.

Engage the automatic feed on “fast”

cut and watch for proper machining action. If necessary, repeat this step until all damaged surface areas have been removed on both sides of the rotor. Some single-cut machines only have one cutting speed.

Use sandpaper or a drill with a

12 sanding pad to give the rotor faces a nondirectional finish.

CHAPTER 32 Disc Brake System

Determine if the stud can be removed with the flange on or off the vehicle. (Step 1) To perform the drawing-in method, first position the flange so the stud has clearance on the back side to be removed. (Step 2) Remove any damaged studs with a hammer. Be careful not to damage any of the surfaces on the flange and hub, including the wheel speed sensor and tone ring. (Step 3) Insert the stud in the hole in the flange and rotate it so that all of the flutes on the stud line up with the notches in the flange. (Step 4) Place enough heavy duty washers over the stud to prevent the lug nut from bottoming out on the threads. (Step 5) Place the lug nut onto the stud, flat side in. Tighten it until the stud bottoms out in the flange. Inspect the threads on the stud and lug nut to make sure they did not get damaged. (Step 6) To perform the hydraulic press method, first remove the hub and wheel flange from the vehicle following the manufacturerâ&#x20AC;&#x2122;s procedure. (Step 7) Use the press to push out any damaged lug studs. (Step 8) Insert the new lug stud into the wheel flange hole. Line up the flutes on the stud with the notches in the flange. (Step 9) Support the hub and flange so the press is pushing the stud straight into the flange. (Step 10) Push the stud in until it bottoms out in the flange. (Step 11) To complete the drawing-in method and the hydraulic press method, verify that each stud is fully seated in the flange. (Step 12) Reinstall the hub and flange on the vehicle if they were removed. (Step 13)

ÂŠ SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

Wheel studs need to be replaced when they have been damaged or broken off due to improper installation or normal wear and tear. Wheel studs can be damaged by being overtightened and stretched. Look for a neckeddown or thinned-out section of the stud, which is most likely to happen within the threaded area of the stud. Stretched studs need to be replaced. Studs can also have their threads damaged by cross-threading or seizing of the lug nut on the stud. It is best to replace the stud and nut if this occurs. Lastly, wheel studs may even break off if they are overtightened beyond their stretch point. It is always a good idea to consider replacing all of the studs on a wheel (and maybe the ones on the other wheels also) if one stud is broken off, as it is likely that all of the others have been weakened. Some vehicles are designed to allow for the removal and replacement of the wheel studs while the hub and wheel flange are still installed on the vehicle. The manufacturer may have provided a recessed spot in the steering knuckle where the studs have enough clearance to be removed; thus, the flange needs to be positioned in that particular position. Other vehicles do not have enough clearance on the back side for the stud to be removed; thus, the hub and flange must be removed from the vehicle. There are two primary methods of replacing lug studs: the drawing-in method and the hydraulic press method. The drawing-in method uses the lug nut to draw in the wheel stud. It is accomplished by inserting the new stud into the wheel stud hole in the flange, installing enough heavy-duty washers over the stud to allow the lug nut to draw the wheel stud into the flange when tightened. The lug nut is placed flat side in, on the stud, and tightened. Make sure that as the stud is pulled in the lug nut does not run out of threads on the stud. If it does, remove the nut and add washers. Keep tightening the lug nut until the wheel stud bottoms out in the flange. Verify that the head of the stud is fully seated in the flange. The hydraulic press method uses a press to force the wheel stud into the flange until it bottoms out. This method requires the hub and flange to be removed from the vehicle. Make sure the flange is positioned and supported properly on the press table. Sometimes it is best to use a short piece of pipe (a bit longer than the wheel stud) to support the flange while the stud is being pressed in. Once the stud is installed, verify that it is fully seated in the flange. To inspect and replace wheel studs, follow the steps in SKILL DRILL 32-12 : 1 Inspect the wheel studs and lug nuts for damage. Look for signs of stretched studs, cross-threaded lug nuts, and broken-off studs.

Inspecting and Replacing Wheel Studs

7 8 9

10 11

12 13 14

Installing Wheels, Torquing Lug Nuts, and Making Final Checks This step, while fairly simple, can result in problems if it is not done properly. Overtightening the lug nuts can cause the wheel studs to break either immediately, or worse, after the vehicle has been driven for a period of time. Overtightening also can cause warpage of the rotors, which results in the need to refinish or replace them. Undertightening can lead to loosening of the lug nuts and result in the wheel working its way off the vehicle. This can cause the driver to lose control of the vehicle and potentially result in an accident. Lug nuts should be tightened to the

section vi BrakeS

must match the mating surface of the wheel. Always check that these surfaces match. When installing lug nuts, the weight should be off the vehicle so that the wheel is off the ground or is barely touching the ground. The lug nuts should easily center the wheel on the hub. This is especially important on aluminum wheels that use a fl at lug nut seating surface. The lug nuts can dig into the sides of the lug nut holes

proper torque, in the specifi ed sequence. All manufacturers specify the sequences for each of their vehicles. The torque pattern is usually in some form of a star or cross. Be careful which way you install the lug nuts. Many wheels use a tapered hole that matches the tapered end of the lug nut and centers the wheel on the wheel fl ange. Other wheels use a fl at surface that matches fl at surfaces on the lug nuts. But no matter what, the lug nut surface

Inspecting and Replacing Wheel Studs

32-12

SKILL DRILL

Inspect the wheel studs and lug

nuts for damage. Look for signs of

stretched studs, cross-threaded lug nuts, and broken-off studs. Determine if the stud can be removed with the flange on or off the vehicle.

Insert the stud in the hole in the

flange and rotate it so that all of

the flutes on the stud line up with the notches in the flange.

To perform the drawing-in

method, position the flange so

the stud has clearance on the back side to be removed.

Place enough heavy-duty washers

over the stud to prevent the lug nut from bottoming out on the threads.

Remove any damaged studs

with a hammer. Be careful not to

damage any of the surfaces on the flange and hub, including the wheel speed sensor and tone ring.

Place the lug nut onto the stud,

flat side in. Tighten it until the stud bottoms out in the flange. Inspect the threads on the stud and lug nut to make sure they did not get damaged.

chapter 32 Disc Brake System

32-12

Inspecting and Replacing Wheel Studs, continued

SKILL DRILL

To perform the hydraulic

press method, remove the hub

and wheel flange from the vehicle following the manufacturer’s procedure.

Support the hub and flange so the

10 press is pushing the stud straight into the flange.

Reinstall the hub and flange on the

13 vehicle if it was removed.

Use the press to push out any

damaged lug studs.

Push the stud in until it bottoms

11 out in the flange.

Insert the new lug stud into the

wheel flange hole. Line up the

flutes on the stud with the notches in the flange.

To complete the drawing-in

12 method and the hydraulic press method, verify that each stud is fully seated in the flange.

SECTION VI BRAKES

ÂŠ SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

There is some controversy regarding the use of a lubricant or antiseize on wheel studs and lug nuts. Since the purpose of a lubricant or antiseize is to prevent the components from sticking, CDX errs on the side of not using those products, for fear of the lug nuts coming loose. Also, the torque given for the lug nuts is dry (no lubricant) so torquing them to specifications would lead to overtorquing. At the same time, in areas of the country prone to rust, it is understandable why some want to put a very light amount of antiseize only on the threads of the wheel stud, being careful not to get any on the contact seat of the wheel and lug nut. Doing so would prevent rust from building up on the threads. However, the lug nut torque would need to be reduced due to the lubricant. CDX prefers to install lug nuts dry and avoid this issue altogether. Many shops have their customers sign on the repair order that they will return and the wheel torque will be rechecked after 50 to 500 miles of driving to make sure the wheels have not loosened.

process of transferring pad material onto the rotor evenly, as well as cooking off the resins that are used to bind the friction material together in the pad. Burnishing results in long, quiet brake life, which results in satisfied customers. For burnishing to happen properly, the rotor and pad material need to be heated slowly and evenly. This is done by making a specified number of stops from a specified speed, with the appropriate wait times between stops. In some cases, brake lining manufacturers want you to perform a series of stops at light to moderate brake application. Other manufacturers specify a series of moderate to heavy stops. Always check the manufacturerâ&#x20AC;&#x2122;s procedure to burnish the brakes once the brake job is complete. This process will help avoid the dreaded disc brake squeal. To install the wheel, torque lug nuts, and make final checks and adjustments, follow the steps in SKILL DRILL 32-13 : 1 Start the lug nuts on the wheel studs. Make sure the lug nut surface matches the wheel hole. The lug nuts should be able to be turned by finger. (Step 1) 2 Carefully run all of the lug nuts down so they are seated in the wheel. Make sure the wheel is centered on the hub. (Step 2) 3 Lower the vehicle so the tires are partially on the ground to keep them from turning while tightening the lug nuts. (Step 3) 4 Use a torque wrench to tighten each lug nut to the proper torque in the proper sequence. (Step 4)

TECHNICIAN TIP

and cause the wheel to not center properly. Once the lug nuts are against the wheel, work the wheel onto the lug nut shafts. Then you can torque them down properly. Once the lug nuts are torqued properly and the brake system checked, it is time for a test drive to verify proper brake operation, and to burnish the new brake pads and rotor surfaces. Burnishing, also called bedding in, is the

SKILL DRILL

32-13

Start the lug nuts on the wheel studs, being careful to match up the surfaces.

Installing Wheels, Torquing Lug Nuts, and Making Final Checks

Carefully run all of the lug nuts down so they are seated in the wheel.

Lower the vehicle so the tires are partially on the ground to keep them from turning while tightening the lug nuts.

CHAPTER 32 Disc Brake System

32-13

Installing Wheels, Torquing Lug Nuts, and Making Final Checks, continued

ÂŠ SA 20 M 12 PL Jo E ne C s H & AP B TE art R let O tL N ea LY r n

SKILL DRILL

Use a torque wrench to tighten each lug nut to the proper torque in the proper sequence.

Check the brake fluid level in the master cylinder reservoir. Start the vehicle and check the brake pedal for proper feel and height. Check the parking brake for proper operation. Also inspect the system for any brake fluid leaks and loose or missing fasteners.

Once all of the lug nuts have been torqued, go around them again, this time in a circular pattern to ensure that you did not miss any in the previous pattern.

Once all of the lug nuts have been torqued, go around them again, this time in a circular pattern to ensure that you did not miss any in the previous pattern. (Step 5) If the vehicle was equipped with hubcaps and valve stem caps, reinstall them. (Step 6)

7 8

If the vehicle was equipped with hubcaps and valve stem caps, reinstall them.

section vi BrakeS

Wrap-up

 Disc brakes create braking power by forcing fl at friction pads against the outer faces of a rotor.  The vehicle’s kinetic energy is transformed into heat energy by the disc brake components, which slow the vehicle when applied.  Disc brake assemblies consist of a caliper, brake pads, and a rotor.  Caliper pistons use hydraulic pressure to create a clamping force of the brake pads to the faces of the rotor.  Disc brake pads require much higher application pressures to operate than drum brake shoes, Summarizes chapter content because they are not self-energizing. in a comprehensive  Advantages of disc brakes over drum brakes: more bulleted list. effective at transferring heat to the atmosphere, self-adjusting, resistant to water fade, and easier to service.  Disadvantages of disc brakes compared to drum brakes: more prone to noise, more prone to pedal pulsations due to warpage, and more diffi cult to use as an emergency brake.  Disc brake calipers come in two main styles: fi xed and fl oating/sliding.

 In disc brake calipers, the piston is sealed by a square cut O-ring.  Floating/sliding calipers require clean and lubricated pins, bushings, or guides for proper operation.  Brake pad lining is either riveted or bonded to the pad backing plate.  Brake pad lining is available in a variety of materials with varying amounts of coeffi cient of friction.  Brake pads may use shims, spacers, guides, and bendable tangs to help minimize squealing.  Brake pad wear indicators, if used, can be of the mechanical or electronic type.  Rotors rotate with the wheels and are usually made of durable cast iron with friction surfaces that run true and parallel.  Brake rotors can be solid or ventilated.  Disc brake parking brakes can be of the integrated caliper style, top hat drum style, electric pull-cable style, and the integrated electric motor caliper style.  Diagnosing brake faults requires good information from the customer, an adequate test-drive when possible, and a good understanding of brake theory.

Ready for Review

chapter 32 Disc Brake System

Key Terms

drawing-in method A method for replacing wheel studs that uses the lug nut to draw the wheel stud into backing plate A metal plate to which the brake lining the hub or flange. is fixed. edge code A code printed on the edge of a friction bendable tangs Small tabs on the brake pad back lining that describes its coefficient of friction. ing plate that are crimped on to the caliper, creating a electronic control module (ECM) A computer that secure fit and reducing noise. receives signals from input sensors, compares that bearing races Hardened metal surfaces that roller or ball information with preloaded software, and sends an bearings fit into when a bearing is properly assembled. appropriate command signal to output devices; used to bleeder screw A screw that allows air and brake manage the anti-lock brake system (ABS). uid to be bled out of a hydraulic brake system when fixed caliper A type of brake caliper bolted firmly to fl it is loosened and seals the brake fluid in when it is the steering knuckle or axle housing, having at least one t ightened. piston on both sides of the rotor. bonded linings Brake linings that are essentially glued guide pins Pins that allow the caliper to move in and to the brake pad backing plate; more common on out as the brakes operate and as the brake pads wear. light-duty vehicles. hydraulic press method A method for replacing wheel brake booster A vacuum or hydraulically operated studs that uses a press to force the wheel stud into the d evice that increases the driver’s braking effort. flange until it bottoms out. brake lining thickness gauge A tool used to measure independent rear suspension (IRS) A type of suspenthe thickness of the brake lining. sion system where each rear wheel is capable of moving sion system where each pieces of of metal metal independently of the other. brake pad shims and guides Small Small pieces independently of the that cushion the brake pad and absorb absorb Provides some of of a the the some list of key termsrunout Also and lateral called warpage, the side-to-side runout Also vibration, helping to cut down on unwanted noise. unwanted noise. from the definitions chapter. movement of the rotor surfaces as the rotor turns. movement of the rotor brake wash station A piece of equipment equipment designed designed low-drag caliper A caliper designed to maintain a caliper caliper A to safely clean brake dust from drum drum and and disc disc brake brake larger larger brake brake pad-to-rotor pad-to-rotor clearance by retracting the components. pistons farther than normal. farther than bushing An insert with an inner bearing surface that lug A flange that is shaped to assist with aligning is fitted into a hole in an object, allowing the object to o bjects on other objects. rotate or slide on a pin or shaft. off-car brake lathe A tool used to machine (refinish) caliper A hydraulic device that uses pressure from the drums and rotors after they have been removed from master cylinder to apply the brake pads against the rotor. the vehicle. caliper dust boot seal driver set A set of drivers used on-car brake lathe A tool used to machine (refinish) to install metal-backed caliper dust boot seals. rotors while they are still attached to the vehicle. caliper piston pliers A tool used to grip caliper pistons parallelism Also called thickness variation; both surwhile removing them. faces of the rotor should be perfectly parallel to each caliper piston retracting tool A tool used to retract other so that brake pulsations do not occur. caliper pistons on integrated parking brake systems. parking brake cable pliers A tool used to install parkC-clamp A tool used to push pistons back into the ing brake cables. c aliper bore on non-integrated parking brakes. phenolic resin A material used to create some brake pisdial indicator Tool used to measure the lateral runout tons that is very resistant to corrosion and heat transfer. of the rotor. pushrod (braking system) A mechanism used to transdisc brake pads Brake pads that consist of a friction mit force from the brake pedal to the master cylinder. material bonded or riveted to a steel backing plate; riveted linings Brake linings riveted to the brake pad designed to wear out over time. backing plate with metal rivets and used on heavierdisc brake rotor micrometer A specially designed duty or high-performance vehicles. micrometer used to measure the thickness of a rotor. rotor The main rotating part of a disc brake system.

section vi BrakeS

steering knuckle A device that connects the front wheel to the suspension; pivots on the top and bottom, thus allowing the front wheels to turn. ventilated rotor A type of brake rotor with passages between the rotor surfaces that are used to improve heat transfer to the atmosphere. wheel studs Threaded fasteners that are pressed into the wheel hub flange and used to bolt the wheel onto the vehicle.

scratcher A thin, spring steel wear indicator that is fixed to the backing plate of the brake pad; it emits a high-pitched squeal when the brakes are applied if the brake pads have become too thin. sliding or floating caliper A type of brake caliper that only has piston(s) on the inboard side of the rotor. The caliper is free to slide or float, thus pulling the outboard brake pad into the rotor when braking force is applied. solid rotor A type of brake rotor made of solid metal. square cut O-ring An O-ring with a square crosssection that is used to seal the pistons in disc brake c alipers.

chapter 32 Disc Brake System

1. Tech A says that disc brakes operate on the princi-

spring-steel brake pad wear indicator. Tech B says that some vehicles are equipped with an electric brake pad wear sensor that activates a warning on the dash. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 8. Tech A says that rotors should be measured for thickness variation. Tech B says that rotors should be measured for lateral runout. Who is correct? a. Tech A Familiarize students with the b. Tech B format of the ASE certification c. Both A and B and Bexamination and test students’ d. Neither A nor B A norunderstanding B of content. 9. Tech A says says that that brake brake pedal pedal pulsation pulsation can can be be caused by a rotor that is too thin. Tech B says that rotor that is too thin. Tech B says that brake pedal pulsation pulsation can can occur occur when when activating activating the ABS. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 10. Tech A says that a micrometer is used to measure rotor thickness variation. Tech B says that a m icrometer is used to measure rotor lateral runout. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B

ple of friction. Tech B says that disc brakes operate on the principle of regeneration. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 2. Tech A says that some vehicles use fixed calipers. Tech B says that some vehicles use sliding /floating calipers. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 3. Tech A says that disc brakes require higher application pressures than drum brakes. Tech B says that disc brakes are self-energizing. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 4. Tech A says that fixed calipers use one or more pistons only on one side of the rotor. Tech B says that sliding /fixed calipers use one or more pistons on both sides of the rotor. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 5. Tech A says that calipers use a round section O-ring to seal each piston. Tech B says that calipers use a square section O-ring to seal each piston. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B 6. Tech A says that brake fade is when the brake pedal is soft and spongy. Tech B says that brake fade is when the wheels skid during a panic stop. Who is correct? a. Tech A b. Tech B c. Both A and B d. Neither A nor B

7. Tech A says that some vehicles are equipped with a

ASE-Type Questions

STEERING AND SUSPENSION 27 Servicing Wheels 28 Servicing Steering Systems 29 Servicing Suspension Systems

Automotive Technology

MANUAL TRANSMISSION 22 Manual Transmission/Transaxle Principles 23 Clutch System 24 Manual Transmissions/Transaxles 25 Drive Train Components 26 Basic Drive Layouts

FUNDAMENTALS OF

Principles and Practice

SAFETY AND FOUNDATION 1 Careers in Automotive Technology 2 Introduction to Automotive Technology 3 Introduction to Automotive Safety 4 Personal Safety 5 Vehicle, Customer, and Service Information 6 Tools and Equipment 7 Vehicle Protection and Jack and Lift Safety 8 Vehicle Maintenance Inspection 9 Communication ENGINE REPAIR 10 Engine Mechanical Testing 11 Engine Removal and Replacement 12 Cylinder Head Components 13 Engine Block Components 14 Engine Machining 15 Engine Assembly

AUTOMATIC TRANSMISSION 16 Automatic Transmission Fundamentals 17 Hydraulic Fundamentals 18 Hydraulically Controlled Transmission 19 Electronically Controlled Transmission 20 Servicing the Automatic Transmission 21 Hybrid and CVT Transmissions

BRAKES 30 Principles of Braking 31 Hydraulics and Power Brakes 32 Disc Brake System 33 Drum Brake System 34 Wheel Bearings 35 Electronic Brake Control ELECTRIC 36 Principles of Electrical Systems 37 Meter Usage and Circuit Diagnosis 38 Batteries, Starting, and Charging Systems 39 Lighting Systems 40 Body Electric System HVAC 41 Principles of Heating and Air-Conditioning Systems 42 Heating and Air-Conditioning Systems and Servicing 43 Electronic Climate Control ENGINE PERFORMANCE 44 Motive Power Types - SI Engines 45 Engine Lubrication 46 Engine Cooling 47 Ignition Systems Overview 48 Gasoline Fuel Systems 49 On-Board Diagnostics 50 Induction and Exhaust 51 Emission Control 52 Alternate Fuel Systems DIESEL ENGINES 53 Compression-Ignition Engines 54 Diesel Fuel Systems

Source Code:SAFATbr