tests you conduct is done before you get out of the car when you have brought it into the that is:
Brake Pedal Check
BRAKE SERVICING
MASTER CYLINDERS AND BRAKE FLUID
mer complained about “loss of brake mentioned it only happened once when the traffic lights and it has PART TWO Issuenot 14/2017 . This is an early warning sign SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS rning, Will Robinson!!) AND WHEEL ALIGNMENT SPECIALISTS
Whatthe do brake you look for when gine, pump pedal a fewchecking times the brake master cylinder for serviceability? uum booster to atmospheric pressure
Like any other component that receives constant use, the master cylinder eventually wears out. Stop-andgo city driving is a lot harder on a master cylinder than highway driving, so a master cylinder that travels on the brake lightinpressure, 150,000pedal or morewith kilometres one vehicle may only last 120,000 kilometres in another. enough to move it. If the master cylinder is faulty,
Light constant pressure.
This syndrome can also be caused a by sticking a modulator valve in the ABS control unit. The loss of the brake pedal caused by the unit may only manifest itself after the ABS was activated. The only fix is to replace the unit as they are not repairable.
Loss of Brake Fluid but no Visible Signs of Leakage
the pedal willaround gradually creep tofor the floor, Inspect the area the master cylinder fluid leaks. If you notice any brake fluid leaking out of the the cups and master the cylinder bore inside the master cylinder, then it is not functioning properly and The creeping brake pedal check is one of the first tests likely need to beto replaced. is in need of overhauling or being replaced. Note: itwillismost recommended replace the unit. you should conduct when driving the vehicle into the Creeping Brake Pedalthe Check fluidThe is bypassing between rubber
If you cannot detect any signs of fluid but the back reservoir constantly requires up” there is abrake can alsoHasbeyour caused bycomplained stickingabout modulator valve in the ABS control unit.“topping The loss of the customer “loss of brake good chance the rear seal in the master cylinder has pedal”? Have they mentioned it only happened once failed allowing fluid to ingress y the unit may only manifest itself after the ABS was activated. The only the fixmaster is tovac. replace the when they were sitting at the traffic lights and it has not On rare occasions, the car may exhaust smoke, this is happened since. This is an early warning sign. ot repairable. caused by the brake fluid being taken into the engine via Turn off the pump the brake pedal a few times to the vacuum hose. Check the hose for dampness. e master cylinder forengine, serviceability? bring vacuum booster to atmospheric pressure (no fluid but notheVisible Signs: vacuum). nt use, the master cylinder eventually wears out. Stop-and-go workshop.
Master Cylinders and Brake Fluid
Rest your foot on the brake so pedal with light pressure, er cylinder than highway driving, a master cylinder that
not much, just enough to move the master cylinder aation around master cylinder forit. Iffluid leaks. If you mayis the only last 120,000 kilometres in another faulty, the pedal will gradually creep to the floor, e fluid leaking out of the master cylinder, then it indicating that the fluid is bypassing between the rubber e you getcups out of the when youlikely have brought into ng properly and will most need toit cylinder be the and thecar cylinder bore inside the master and it is in need of overhauling or being replaced. Note: it is recommended to replace the unit.
etect any signs of fluid but the back reservoir
brake ires “topping up”. There is a good chance the eerwhen cylinder has failed and allowing fluid the
ter vac.
rear
Light constant pressure.
ons, the car may exhaust smoke, this is caused by w times taken into the engine via the vacuum hose. Check the hose for dampness. being
essure
essure, cylinder is faulty, the pedal will gradually creep to the floor, he rubber cups and the cylinder bore inside the master ng replaced. Note: it is recommended to replace the unit.
Straight advice, specialists you understand and...
modulator valve in the ABS control unit. The loss of the brake elf after the ABS was activated. The only fix is to replace the
BRAKE SERVICING
MASTER CYLINDERS AND BRAKE FLUID
ake Drag:
Issue 14/2017
PART TWO
s is when hydraulic pressure is not fully released after the pressure on the brake pedal has been released ABSORBER, SUSPENSION, BRAKES, TOWBARS there is still residual brake line pressure inSHOCK the system. AND WHEEL ALIGNMENT SPECIALISTS
at are the symptoms?: Brake Drag
• • • • • • •
at
• • • • • • •
Soft or Long Travel Brake Pedal
This is when hydraulic pressure is not fully released after
A common problem and a question that is asked quite
• Loss of brake pedal, as fluid might have overheated.
pulled out. This can be difficult to detect but will hinder a
Poortheeconomy. pressure on the brake pedal has been released and often, is “Why does my pedal feel soft?” One of the most there is still residual brake line pressure in the system. overlooked things is probably the simplest fix. Overheating brakes (blue Rotors). Brake Drag: What theengine symptoms? Extending out of the booster is a pin. This pin simply Feels likearethe has lost power. extends into the piston in the back of the master • Poor economy. This is when hydraulic pressure is not fully released after cylinder. the pressure on the brake pedal has been released Premature wear of brake Pads or Shoes. Have you ever checked this distance? If you and• there is still residual brake line pressure in the system. brakes (blue Rotors). answered no, not only is this something you must do, Loss Overheating of brake pedal, as fluid might have overheated. it may be the reason for the soft pedal. Diagram 2 can • Feels like symptoms?: the engine has lost power. What are the ABS Modulator may activate. have two problems, not enough clearance or too much. • Premature wear of brake Pads or Shoes. Theover reaction disc can be dislodged when the push rod is Brake pedal vibration, possible warped rotors from heating. • Poor economy.
Overheating brakes (blue Rotors). good brake pedal. causes• •ABS this?: Modulator may activate. • Feels like the engine has lost power. It is recommended that the distance between the pin • pedal vibration, warped •Brake Premature wear ofpossible brake Pads or rotors Shoes.from from the booster and the hole in your master cylinder No brake pedal free play. heating. be approximately 0.5mm. If this distance is greater than •over Loss of brake pedal, as fluid might have overheated. 0.5mm, when you first push the pedal, you(diag. will have No clearance between the push rod of the booster to the master cylinder piston. 1)to What causes this? • ABS Modulator may activate. overcome this distance and get the pin to the master Brake booster internal reaction disc faulty or not enough clearance. (diag. 2) Brake pedal vibration, possible warped rotors fromcylinder. over heating. • •No brake pedal free play. This will cause your soft pedal. If the distance
is less than the master cylinder not be Cups incauses the master cylinder contaminated and increased in0.5mm, size and blocking themay fluid return port. • No clearance What this?:between the push rod of the booster to returning the entire amount and therefore causing a the master cylinder piston. (diag. 1) Driver error, bad habit of resting foot on brake pedal. different problem of brake drag. •Brake NoDOT brake brake pedal free play. • booster internal reaction faulty or not Incorrect fluid in disc system. clearance.between (diag. 2) the push rod of the booster to the master cylinder piston. (diag. 1) •enough No clearance Contamination of brake fluid, mixed with mineral oil.
•Cups Brake reaction discand faulty or not enough clearance. • in thebooster master internal cylinder contaminated increased in size and blocking the fluid return port. • Cups in the master cylinder contaminated and increased in size and Driver bad habit of resting brake • •Driver error,error, bad habit of resting foot on foot brakeonpedal. Incorrect in system. • •Incorrect DOTDOT brakebrake fluid influid system. •
pedal.
(diag. 2) blocking the fluid return port.
Contamination of brake fluid, mixed with mineral oil.
• Contamination of brake fluid, mixed with mineral oil.
0.5mm
0.5mm Diag. 2
Diag. 1 Diag.11 Diag.
t or Long Travel Brake Pedal:
Soft or Long Travel Brake Pedal:
ommon problem and a question that is asked quite often , is “Why does my pedal feel soft?” in my Straight advice, specialists you understand and... wer brake system. One of most overlooked things is probably the simplest fix.soft?” in my A common problem andthe a question that is asked quite often , is “Why does my pedal feel power brake system. One of the most overlooked things is probably the simplest fix.
BRAKE SERVICING
MASTER CYLINDERS AND BRAKE FLUID Issue 14/2017
PART TWO
SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
Brake Fluid
Brake Fluid:
Wet Boiling Point
Brake fluid is another source for a soft or “doughy” brake This is a similar test to the Dry Boiling Point, but this time Brake fluid is another source for a soft or “doughy” brake pedal. Brake fluid has a limited life and definitely pedal. Brake fluid has ahas limited and definitely has a performed on the fluid after it has had time to absorb a “uselife by date”. “use by date”. moisture from its surroundings. Specifically called the Because brake fluid is Hygroscopic, which means it absorbs water, the Boiling integrity Point diminishes that thethis is Wet Equilibrium Reflux (WetinERBP), Because brake fluid is Hygroscopic, which means boiling point drops as the moisterit content rises. the temperature the fluid begins to boil when tested in absorbs water, the integrity diminishes in that the boiling witha gas the(air) DOT procedure. An interesting Because there isrises. moisture in the fluid, when accordance it boils, it creates and we are all aware gases are fact point drops as the moisture content that thea fluid being not checked for moisture compressible where fluids are not. When thisishappens spongy braketested pedal isisexperienced and the Because there is moisture in theoffluid, when it boils, content, but a reference fluid sitting close to it is. When efficiency braking ability of the car is affected. it creates a gas (air) and we are all aware gases are the reference fluid reaches 3.70%±0.05% water content It is recommended thatthis all vehicles with DOT 4, Dot 5.1, brake fluid should have it changed compressible where fluids are not. When happens a DOT by3,weight, the fluid being tested is then put through the between 2 to 3 years, under normal operating conditions and even more often under extreme conditions. spongy brake pedal is experienced and the efficiency of same procedure as for Dry ERBP to get the Wet ERBP. braking ability of the car affected. Allisbrake fluids must comply to a minimum standard. Under this standard are four DOT minimum specifications for brake fluids. They are DOT 3, DOT 4, and DOTViscosity 5.1 for fluids typically based with Polyalkylene Glycol Ether and
All brake fluids must comply to a minimum standard. DOT 5 for silicone-based fluids. This is where the DOT 3 spec could be interpreted as Under this standard areWarning: four DOT minimum DOT 5 is not compatible with any of the Glycol based brake fluids. actually being better for the miniature passages of an specifications for brake fluids. They are DOT 3, DOT 4, ABS system than the DOT 4 spec. Thinking about motor and DOT 5.1 for fluids typically based with Polyalkylene oil, the higher the viscosity number, the slower the flow Dry Boiling Point Glycol Ether and DOT 5 for silicone-based fluids. For all DOT-compliant fluids, this is the of the (thicker) oil. The same basic principle applies to It is recommended that all has vehicles 3, DOT 4,to boilbrake fluid, although the measurement technique is temperature at with which the begins soft or “doughy” brake pedal. Brake fluid a limited lifeDOT andfluid definitely tested in it changed between and Dot 5.1 brake fluid when should have different. The DOT 3 specification for viscosity at -40°F is the manner specifically described 2 to 3 years, under normal operating conditions andby the 1500 mm2/s, where DOT 4 is 1800 mm2/s. So, the DOT c, which means it absorbs water, the integrity diminishes in that theEquilibrium The correct term is the even more often underDOT. extreme conditions. content rises. Reflux Boiling Point (ERBP). This basically3 fluid flows better at the cold testing temperature than means the fluid is tested brand-new, right outthe DOT 4. Warning: DOT 5 is not compatible with any of the Glycol uid, when it boils, it creates a gas (air) of anda freshly we are all awarebottle, gasesbefore are being opened based brake fluids. When this happens a spongy brake pedal is experienced and the car is affected. Dry
Boiling Point
contaminated by moisture.
Wet should Boilinghave Point s with DOT For 3, DOT 4, Dot 5.1, brake fluid it changed all DOT-compliant fluids, is the at This is this a similar testtemperature to the Dry Boiling l operating conditions even more often under extreme conditions. which theand fluid begins to boil when tested in the manner Point, but this time performed on the fluid after it has hadcorrect time to term absorbis specifically described by the DOT. The
nimum standard. Under this standard are four DOT minimum specifications for moisture from its surroundings. the Reflux Boiling Point (ERBP). Thisand basically , and DOT 5.1 forEquilibrium fluids typically based with Polyalkylene Glycol Ether
Specifically called the out Wet of Equilibrium means the fluid is tested brand-new, right a freshly
Reflux contaminated Boiling Point by moisture. with any of theopened Glycol based brake fluids. being bottle, before
is the ins to boil
by the librium s basically w, right out being
(Wet ERBP), this is the temperature the fluid begins to boil when tested in accordance with the DOT procedure. An interesting fact is that the fluid being tested is not checked for moisture content, but a reference fluid sitting close to it is. When the reference fluid reaches 3.70%±0.05% water content by weight, the fluid being tested is then put through the same procedure as for Dry ERBP to get the Wet ERBP.
iling he b
Viscosity This is where the DOT 3 spec could be interpreted as actually being better for the miniature passages of an ABS system than the DOT 4 spec. Thinking about motor oil, the higher the viscosity number, the slower the flow of the (thicker) oil. The same basic principle applies to brake fluid, although the measurement technique is different. The DOT 3 specification for viscosity at -40°F is 1500 mm2/s, where DOT 4 is 1800 mm2/s. So, the DOT 3 fluid flows better at the cold testing temperature than the DOT 4.
brium
Straight advice, specialists you understand and...
re the
BRAKE SERVICING
MASTER CYLINDERS AND BRAKE FLUID Issue 14/2017
PART TWO
SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
How does brake fluid become contaminated? Moisture can (and does) enter a brake system in several ways. The most common are: • Using old or pre-opened fluid. Keep moisture out by only using fluid from tightly sealed bottles and not storing them for long periods of time. • When changing or bleeding brake fluid, always replace master cylinder caps as soon as possible to prevent moisture from entering into the reservoir. • Condensation (small moisture droplets) can form in lines and calipers. As caliper and line temperatures heat up and then cool repeatedly, condensation occurs, leaving behind moisture/water. When water reaches 212ºF at ambient pressure, it turns to steam. The build up of steam will create pressure in the system, sometimes to the point that caliper pistons are pushed into the brake pad. The resulting brake drag creates even more heat in the system. Many times air in the brake system is a result of water that has turned to steam and cooled back down, leaving spongy pedal. • Diffusion through rubber brake hoses over a period of time.
Techstop Hints • When checking the serviceability of the brake fluid,
which should be done at every service check, take samples from the master cylinder reservoir and one front caliper* and one rear caliper*. The reason for this is: 1) They are closest the flexible brake hose. 2) This is where the temperature extremes vary the most.
• Only use the DOT rating brake fluid that is recommended by O.E.M. The reason being, if the car is subject to cold temperatures, the viscosity may affect the operation of the ABS. • When flushing the hydraulic system, it may be necessary to use a scan tool to activate the ABS module, as this will purge all the contaminated fluid from the complete system. • When replacing the Master Cylinder, “Bench” bleed it before fitting it to the car, this could save time and there is a good chance that all the air be will expelled from the new unit and the bleeding process will be easier. Also it will not be as messy. • When bleed or flushing the hydraulic system, place a block of wood under the brake pedal, so the pedal does NOT go to the floor and push the piston to the end of the cylinder and pick up solid contaminates. Especially on old units. • Flushing or bleeding is generally a two person operation, make sure the reservoir is topped up regularly. You do not want to run dry as the process will have to start all over again. • Vacuum out the old fluid from the reservoir, clean out the reservoir and top up with fresh new fluid prior to commencing. It would be best practice not to flush old contaminated fluid through the system. • When changing brake pads and a flush is not scheduled, clamp the flexible hose, place the bleed hose on the bleed nipple, open it and then push back the piston, then close the nipple. This will get rid of the brake fluid that has experienced extreme fluctuations in temperature. Place the new pads, pump the brake pedal and top up the master cylinder.
• The brake fluid should be changed at a minimum period of 24 months.
Straight advice, specialists you understand and...