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Suspension SystemsSuspension Systems

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Purpose of Suspension SystemsPurpose of Suspension Systems

• isolate passengers from pot holes & bumpsisolate passengers from pot holes & bumps

• support the weight of the vehicle and its’ support the weight of the vehicle and its’ loadload

• maintain tire contact with road surfacemaintain tire contact with road surface

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Suspension System ComponentsSuspension System Components

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Suspension SpringsSuspension Springs

• springs sit between the frame or body and the axlessprings sit between the frame or body and the axles

• the spring absorbs irregularities in the road surfacethe spring absorbs irregularities in the road surface

a) torsion barsa) torsion bars

b) coil springsb) coil springs

a

b

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Types of Suspension SpringsTypes of Suspension Springs

c) leaf springsc) leaf springs oldest form of suspension springoldest form of suspension spring can be multi-leafcan be multi-leaf or single, fiberglass “mono-leaf”or single, fiberglass “mono-leaf”

d) air bagsd) air bags now obsolete in automotive usenow obsolete in automotive use ““hot rods” & custom cars often use air bagshot rods” & custom cars often use air bags used on many tour buses and highway trucks & trailersused on many tour buses and highway trucks & trailers

d

c

d

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Control ArmsControl Arms• control armscontrol arms act as pivot points for the steering knuckle act as pivot points for the steering knuckle• control arms or strut rods also prevent fore/aft movement of the tire during braking, control arms or strut rods also prevent fore/aft movement of the tire during braking,

acceleration and turnsacceleration and turns• the inner end of the control arm mounts to the frame or bodythe inner end of the control arm mounts to the frame or body

mounted via a rubber or urethane bushingmounted via a rubber or urethane bushing• the other end is attached to the steering knuckle through a the other end is attached to the steering knuckle through a ball jointball joint

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Shock AbsorbersShock Absorbers• shocks are dampersshocks are dampers• springs actually absorb shocksprings actually absorb shock• shocks DO NOT support the weight of the vehicleshocks DO NOT support the weight of the vehicle• without shocks, springs would compress & rebound many timeswithout shocks, springs would compress & rebound many times• spring oscillations are slowed by forcing hydraulic fluid through tiny passagesspring oscillations are slowed by forcing hydraulic fluid through tiny passages

this is the principle of fluid displacement this is the principle of fluid displacement

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Gas Charged ShocksGas Charged Shocks

• gas charging is not a required part of a shock absorbergas charging is not a required part of a shock absorber

• gas charging is an improvement to a conventional shockgas charging is an improvement to a conventional shock

• gas charging minimizes aeration of the hydraulic fluidgas charging minimizes aeration of the hydraulic fluid

• nitrogen gas compresses the hydraulic fluid nitrogen gas compresses the hydraulic fluid

• this prevents the oil and air from mixing and creating foam this prevents the oil and air from mixing and creating foam

• foam affects performance because air can be compressed - fluid cannotfoam affects performance because air can be compressed - fluid cannot

• with aeration reduced, the shock is able to react faster and more with aeration reduced, the shock is able to react faster and more predictably, allowing for quicker response time and helping keep the tire predictably, allowing for quicker response time and helping keep the tire firmly planted on the road surface firmly planted on the road surface

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Adjustable ShocksAdjustable Shocks

• some aftermarket shocks can have the orifice size adjustedsome aftermarket shocks can have the orifice size adjusted• this adjusts how easily the fluid can move from one chamber to this adjusts how easily the fluid can move from one chamber to

the otherthe other• this alters the shock’s dampening ratethis alters the shock’s dampening rate• this adjustment can be done electronically or manuallythis adjustment can be done electronically or manually

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Anti-roll BarsAnti-roll Bars• anti-rollanti-roll, , stabilizerstabilizer or or swaysway bars help limit body roll during cornering bars help limit body roll during cornering

made of spring steelmade of spring steel• can be used on the front only, or front & rear suspensioncan be used on the front only, or front & rear suspension

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Front Suspension System TypesFront Suspension System Types

• suspension suspension pivotpivot pointspoints, , springssprings & & shocksshocks can be arranged in various can be arranged in various configurations…configurations…

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Short-long arm suspension aka “double wishbone”Short-long arm suspension aka “double wishbone”

• uses upper & lower control armsuses upper & lower control arms• used on many rear-drive domestic carsused on many rear-drive domestic cars• equal length arms would cause tires to scrub across the roadequal length arms would cause tires to scrub across the road

Coilover suspension

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Twin I-Beam suspensionTwin I-Beam suspension

• rugged construction, high unsprung weight rugged construction, high unsprung weight sprung weight: everything supported by the springsprung weight: everything supported by the spring unsprung weight: everything below the springunsprung weight: everything below the spring used on many Ford trucksused on many Ford trucks

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MacPherson strutMacPherson strut• compact, light, low unsprung weightcompact, light, low unsprung weight• very popular suspension designvery popular suspension design• used with unibody constructionused with unibody construction

• modified strutmodified strut used by Fordused by Ford

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Torsion Bar suspensionTorsion Bar suspension• one end fixed to the frame or body structureone end fixed to the frame or body structure

• other end fits into the lower control armother end fits into the lower control arm

• torsion bar twists with control arm movement causing control arm to return to its original torsion bar twists with control arm movement causing control arm to return to its original positionposition

• ride height is adjustable – not possible on coil or leafsride height is adjustable – not possible on coil or leafs

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• torsion bartorsion bar suspension… suspension…

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Multi-link SuspensionMulti-link Suspension

• variation of the double wishbone suspensionvariation of the double wishbone suspension• each arm of the wishbone can pivot independentlyeach arm of the wishbone can pivot independently• helps to keep the tire tread planted on the roadhelps to keep the tire tread planted on the road

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Rear Suspension System TypesRear Suspension System Types

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Solid Axle SuspensionSolid Axle Suspension• may utilize one of the following spring arrangements…may utilize one of the following spring arrangements…• coil springs with control arms (figs. a & b)coil springs with control arms (figs. a & b)

pan hard bar prevents left-to-right axle movement pan hard bar prevents left-to-right axle movement what happens to one tire is transmitted to the other tirewhat happens to one tire is transmitted to the other tire

• leaf springs suspension (figs. c & d)leaf springs suspension (figs. c & d)

a d

c

b

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Solid Axle SuspensionSolid Axle Suspension• air spring suspensionair spring suspension

lighter than a coil spring = lower unsprung weightlighter than a coil spring = lower unsprung weight no frictionno friction has also been used on front suspensionhas also been used on front suspension used on transit and tour buses and many semi trailersused on transit and tour buses and many semi trailers

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Semi-IndependentSemi-Independent

• axle beam flexes to minimize movement from one side to the other over bumps & holes in axle beam flexes to minimize movement from one side to the other over bumps & holes in the roadthe road

• used with MacPherson strutsused with MacPherson struts used on some front wheel drive vehiclesused on some front wheel drive vehicles improved ride & handling over solid axle suspensionimproved ride & handling over solid axle suspension

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Independent – Trailing Arm SuspensionIndependent – Trailing Arm Suspension

• no tire scrubbing – arms positioned front to backno tire scrubbing – arms positioned front to back• takes up a lot of spacetakes up a lot of space

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Independent Long-Short Arm SuspensionIndependent Long-Short Arm Suspension

• short-long arm suspension with coiloversshort-long arm suspension with coilovers used on some rear drive performance vehicles used on some rear drive performance vehicles

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Suspension System RepairSuspension System Repair

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ShocksShocks

check for oil leakscheck for oil leaks

bounce test car on the groundbounce test car on the ground

should bounce once or twice, then stopshould bounce once or twice, then stop

age of vehicle & # of km?age of vehicle & # of km?

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Sway Bar BushingsSway Bar Bushings

• check sway bar mount bushings & outer link kits for wearcheck sway bar mount bushings & outer link kits for wear worn bushings will lead to clunking noisesworn bushings will lead to clunking noises

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Control Arm & Strut Rod BushingsControl Arm & Strut Rod Bushings• visually inspect bushings for deteriorationvisually inspect bushings for deterioration• use a pry bar to check for loosenessuse a pry bar to check for looseness

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Testing Ball JointsTesting Ball Joints• check ball joint sockets for wearcheck ball joint sockets for wear

follow specific inspection procedure in Mitchellfollow specific inspection procedure in Mitchell does the vehicle have lower joint only or upper & lower?does the vehicle have lower joint only or upper & lower? they can break & cause tire to “kick out”they can break & cause tire to “kick out”

leads to loss of control & vehicle damageleads to loss of control & vehicle damage• when replacing ball joints, they can be…when replacing ball joints, they can be…

threaded into the control armthreaded into the control arm pressed into the control armpressed into the control arm riveted to the control armriveted to the control arm

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Broken SpringsBroken Springs• coils, leafs or torsion bars that are weak or broken will cause the vehicle to sag on the coils, leafs or torsion bars that are weak or broken will cause the vehicle to sag on the

affected corneraffected corner

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Removing/Replacing SpringsRemoving/Replacing Springs

follow proper spring removal proceduresfollow proper spring removal procedures!! use proper spring compressorsuse proper spring compressors spring’s stored energy can injure or kill! spring’s stored energy can injure or kill!

Compressing McPherson Strut SpringsCompressing McPherson Strut Springs

• NEVERNEVER loosen/remove the nut at the top of the strut until spring tension has been loosen/remove the nut at the top of the strut until spring tension has been

released by the coil spring compressor!!!released by the coil spring compressor!!!

• the spring should rotate freely when compressed before the nut is removedthe spring should rotate freely when compressed before the nut is removed

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