SHOCK ABSORBER Shock Absorber length, is it Important?
LENGTH
16/03 is important. Contrary to popular belief, length
SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS the entire suspension The purpose of a shock absorber is control spring and body movement throughout AND WHEEL ALIGNMENT SPECIALISTS travel. For this reason the shock absorber must be able to work through the entire distance of the suspension travel. Shock Absorber length, is it Important?
If Contrary the extended length of the shock absorber is to shortThe it other will “top-out” and ifreduce theabsorber extended to popular belief, length is important. problem is that the shock thattravel. has been fitted to the vehicle is too long, in this casehead. the “Topping out” is the term used when the piston inside the shock absorber collides with the cylinder The purpose of a shock absorber is control spring and vehicle suspension experience shock absorber If this allowed to happen continuously, damagetravel. will ensue to the mountscould and possibly thethe internal rebound bodyismovement throughout the entire suspension “Bottoming out”. This term is used when the stop. if “topping-out” allowed to continue, then the extended travel of the shock suspension For Consider this reasonthis, the shock absorber mustwas be able to work absorber is fully compressed, but the suspension still through the entire distance of the travel. trying to pull the shock absorber apart, possibly causing would be emulating the action ofsuspension a slide hammer, has an allowed amount of travel to go. There are two theIffollowing: the extended length of the shock absorber is too short possible scenarios , one, the top of the shaft will make operation of the piston travel. “Topping contact with the top of the body, where the top seal is it will Faulty “top-out” and reduce the extended out” the termto used piston inside themounts shock isDamage thewhen upperthe and lower shock housed and damage will occur. When this happens oil absorber collides the cylinder head. willoil be allowed to escape. Extensive damage will also Damage to with the cylinder head and the unit may leak
occur to the shock absorber mounts, to the point of If this is allowed to happen continuously, damage will possibly becoming separated the body, as well The othertoproblem is that if the shock absorber that has been fitted to the vehicle is from too long, in this caseasthe ensue the mounts and possibly the internal rebound the possibility of damaging the fixed points on the body/ stop. Consider this,could if “topping-out” was allowed vehicle suspension experience the shocktoabsorber “Bottoming out”. This term is used when the shock chassis. continue, then the extended travel of the suspension absorber is fully compressed, but the suspension still has an allowed amount of travel to go. There are two would be emulating the action of a slide hammer, trying possible scenarios , one, the top of the shaft will make contact with the top of the body, where the top seal is to pull the shock absorber apart, possibly causing the housed and damage will occur. When this happens oil will be allowed to escape. Extensive damage will also following:
occur to the shock absorber mounts, to the point of possibly becoming separated from the body, as well as Faulty operation of the piston the• possibility of damaging the fixed points on the body/chassis. • Damage to the upper and lower shock mounts
• Damage to the cylinder head and the unit may leak oil
Stroke
Extended Length Compressed Length
Figure 1
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When the vehicle is designed, the suspension travel is an important factor when calculating the shock absorber’s working length. While the vehicle remains at standard ride height and the correct part numbered shock absorber is fitted to the car, then there will be no issues.
SHOCK ABSORBER
LENGTH
But this is not always the case, as you will find that many vehicles have :
Have had the suspension modified When the vehicle is designed, the suspension travel is an important factor when calculating the shock Had the vehicle raised (S.U.V. or 4 W.D.) absorber’s working length. While the vehicle remains at standard ride height and the correct part numbered Have been lowered excessively shock absorber is fitted16/03 to the car, then there will be no issues. It also may be a private import (vehicle not available in Australia from the dealer) isOr may bethea special But this notitalways case, as use youvehicle will findABSORBER, that manySUSPENSION, vehicles have : SHOCK BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
So, you are of fittingmodified a shock absorber to a vehicle, the three rules in suspension are “Measure, ifHave hadunsure the suspension When the vehicle is designed, suspension is an important factor when calculating the shock absorber’s Measure, Measure”. Had the vehicle the raised (S.U.V. ortravel 4 W.D.) working length. While the vehicle remains at standard ride height and the correct part numbered shock absorber is Have been lowered excessively it comes to determining the correct length of a shock absorberfrom to fitthe andealer) application, you need to adhere fitted to theWhen car, then there will be no issues. It also may be a private import (vehicle not available in Australia totheOrfollowing method: (refer to fig. 2) it may be a special But this is not always the case, as youuse willvehicle find that many vehicles have : So, the if you are unsuremodified of fitting a shock absorber to a vehicle, the three rules in suspension are “Measure, • Have had suspension Measure, Measure”. • Had the vehicle (S.U.V. or 4 W.D.) raised Measure the extended and compressed length of the shock When it comes to determining the correct length of a shock absorber to fit an application, you need to adhere absorber • Have been lowered excessively to the following (refer to fig. 2) type of mount, measure at the base. When method: measuring a “Pin/Pin” • It also may bea private import (vehicle not available in Australia from theofdealer) When measuring a “Loop/Loop” measure to the middle the • Or it may be a special loop. use vehicle Measure the extended andhas compressed length of the shock If the shock a “Pin/Loop”, measure fromrules the bottom So, if you are unsure of fitting aabsorber shock absorber to a vehicle, the three in absorber of the pinMeasure, to the middle of the loop. suspension are “Measure, Measure”. When measuring a “Pin/Pin” type of mount, measure at the base. When it comes determining correct length of a shock fit an to When measuringthe a “Loop/Loop” measure to theabsorber middle oftothe application, youloop. need to adhere to the following method: (refer to fig. 2) extended If the shock absorber has a “Pin/Loop”, measure the bottom • Measure the and compressed length of the shockfrom absorber
of the pin to thetype middle of the loop. • When measuring a “Pin/Pin” of mount, measure at the base. Compressed Length:
Figure 2
• When measuring a “Loop/Loop” measure to the middle the loop. Measure the following distances as per figure 3. & offigure 4. • If the shock absorber has a “Pin/Loop”, measure from the bottom of the pin to the middle of the loop. The shock absorber length when installed (I.L.), with the vehicle at normal ride height. (N.R.H.) Figure 2 The Bump Stop Clearance (B.S.C.) at normal ride height (N.R.H.) Compressed Length: Compressed Length: The Bump Stop Height (B.S.H.) the following distances as per figure figure4.4. Measure Measure the following asusing per figure 3. 3.& &figure How calculatedistances the answer, the following example of the formula.
The shock absorber length when installed (I.L.), the vehicle at normal ride height. (N.R.H.) • The shockabsorber length when installed (I.L.), with the with vehicle at normal ride height. (N.R.H.) Installed theClearance shock absorber The length Bump of Stop (B.S.C.)isat435mm normal ride height (N.R.H.) • The BumpStop Clearance at normal ride height (N.R.H.) The Bump Stop(B.S.C.) Height (B.S.H.) The bump stop clearance is 100mm • The Bump Stop Height (B.S.H.) How calculate the answer, using the following example of the formula. The bump stop height is 95mm How calculate the answer, using the following example of the formula. Installed length of the shock absorber is 435mm ௌு
ଽହ
) = ( Ͷ͵ͷ െ ͳͲͲ െ ) = ( 335 – 63 ) =272mm compressed length Compressed Lengthabsorber = ( ܮܫെ ܥܤ െ Installed length of the shock is 435mm ଵǤହ ଵǤହ The bump stop clearance is 100mm
The bump stop clearance is 100mm The bump stop height is 95mm
The bump stop height is 95mm
ௌு ଽହ ) = ( Ͷ͵ͷ95 െ ͳͲͲ) െ ) = –( 63 335) –=272mm 63 ) =272mm compressed length Compressed = ( ܮܫെBHS ܥܤെ ) ) = ( 435-100Compressed LengthLength = ( IL-BC= ଵǤହ ( 335 compressed length ଵǤହ 1.5 1.5
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SHOCK ABSORBER 16/03 Extended Extended Length:
LENGTH
SHOCK ABSORBER, SUSPENSION, BRAKES, TOWBARS AND WHEEL ALIGNMENT SPECIALISTS
Length:
When shocker absorber the correct extendedlength, length, raise carcar andand placeplace supports under theunder the When checking thechecking shockertheabsorber for thefor correct extended raisethethe supports chassis, not the axle or control arms, as we want the suspension to “hang”. chassis, not the axle or control arms, as we want the suspension to “hang”. Remove the lower mount of the shock absorber and slowly lower the suspension to full droop whilst maintaining some Remove the lower mount of the shock absorber and slowly lower the suspension to full droop whilst maintaining support under the axle or control arm. The reason for this, is not to stress the flexible brake hose at full droop. If there some supportisunder the of axle or to control reason forflexible this, isbrake not hose, to stress flexible brake hosethe at full droop. an amount travel go and arm. there The is tension on the then itthe maybe wise to investigate If there is an amount to go and there is tension on the flexible brake hose, then it maybe wise to investigate fitment ofofa travel longer hose. the fitment of a longer hose. The extended length of the shock with a leaf spring suspension wants to be approximately +12mm. For a coil spring
The extendedsuspension length ofthe theextended shock length with aisleaf spring be approximately +12mm. For a coil required to besuspension approximatelywants 12mmto shorter. The reason for this, is to maintain a spring “trapped coil” at full suspension droop. suspension the extended length is required to be approximately 12mm shorter. The reason for this, is to maintain a “trapped coil” at full suspension droop.
Other things that should be considered: When a raisedOther suspension kitshould has been fitted to a vehicle, there will things that be considered: normally be the requirement to fit “Long stroke Shock Absorbers”
When a raised suspension kit has been fitted to a vehicle, there will
normally be requirement to fit “Long stroke Shock Absorbers” For a shock absorber to the gain extra length, we first increase the shaft length and then increase the body length.
For a shock absorber to gain extra length, we first increase the shaft
length the and then the bodylength length. of the shock has As figure 5 shows, overincrease all extended been increased by 100mm, but the increase of the compressed As figure 5 shows, the over all extended length of the shock has length has only been increased by 50mm, because thecompressed 50mm of been increased by 100mm, but the increase of the shaft length (the blue fit intobythe body. length hassection) only beenwill increased 50mm, because the 50mm of shaft length (the blue section) will fit into the body.
So there is no damage to the shock absorber under full compression, there no increased damage to the absorber under full the bump stopSohas toisbe inshock length by 50mm. compression, the bump stop has to be increased in length by 50mm.
This may be achieved in one of two ways, place a spacer of 50 This bump may bestop achieved onechassis of two ways, place a spacer of 50 mm mm between the andinthe (using 50mm longer between the bump stop and the chassis (using 50mm longer mounting bolts) or replacing the bump stop with a longer unit, with mounting bolts) or replacing the bump stop with a longer unit, with similar compression capabilities. similar compression capabilities.
Standard length
Extended length
Bump Stops Bump All suspensions will Stops have some form of bump and rebound stops, whether it be beam axle, live axle, independent, wishbone or McPherson strut. In a lot of modern cars, the bump stops may now act aswill a secondary load All suspensions have some form of carrying bump and device. rebound stops, wether it be beam axle,
live axle, independent, wishbone or McPherson strut. In a lot of modern cars, the bump The purpose of these are to limit the travel and protect suspension components, stops may now act as a secondary load carrying device. especially theThe shock absorbers. Even if you don’tand seeprotect themsuspension they will components, be there especially purpose of these are to limit the travel somewhere inthe some or form. thethem bump stops is in ansome shape or form. shockshape absorbers. Even ifChecking you don’t see theyand will rebound be there somewhere the bump rebound stopsoverall is an important part of checking thebeen suspension’s important partChecking of checking theand suspension’s condition. If they have foundoverall condition. a new bump stop is be fitted, otherwise there will be NO missing or deteriorated, they haveshock been found missing when or deteriorated, warranty givenIf to new absorbers fitted. a new bump stop is be fitted, otherwise there will be NO warranty given to new shock absorbers when fitted.
NOTE: DO NOT MODIFY A BUMP STOP UNTIL YOU ARE FULLY AWARE OF HOW THIS WILL AFFECT NOTE; THE SUSPENSION TRAVEL AND OTHER STEERING AND SUSPENSION DO NOT MODIFY A BUMP STOP UNTIL YOU ARE FULLY AWARE OF HOW COMPONENTS. THIS WILL AFFECT THE SUSPENSION TRAVEL AND OTHER STEERING AND SUSPENSION COMPONENTS.
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