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Suspension Systems

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Purpose of Suspension Systems

• isolate passengers from pot holes & bumps

• support the weight of the vehicle and its’ load

• maintain tire contact with road surface

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Suspension System Components

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Suspension Springs

• springs sit between the frame or body and the axles

• the spring absorbs irregularities in the road surface

a) torsion bars

b) coil springs

a

b

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Types of Suspension Springs

c) leaf springs

oldest form of suspension spring

can be multi-leaf

or single, fiberglass “mono-leaf”

d) air bags

now obsolete in automotive use

“hot rods” & custom cars often use air bags

used on many tour buses and highway trucks & trailersd

c

d

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Control Arms

• control arms act as pivot points for the steering knuckle

• control arms or strut rods also prevent fore/aft movement of the tire during braking, acceleration and turns

• the inner end of the control arm mounts to the frame or body

mounted via a rubber or urethane bushing

• the other end is attached to the steering knuckle through a ball joint

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Shock Absorbers• shocks are dampers

• springs actually absorb shock

• shocks DO NOT support the weight of the vehicle

• without shocks, springs would compress & rebound many times

• spring oscillations are slowed by forcing hydraulic fluid through tiny passages

this is the principle of fluid displacement

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Gas Charged Shocks

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

• gas charging is an improvement to a conventional shock

• gas charging minimizes aeration of the hydraulic fluid

• nitrogen gas compresses the hydraulic fluid

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

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

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

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Anti-roll Bars

• anti-roll, stabilizer or sway bars help limit body roll during cornering

made of spring steel

• can be used on the front only, or front & rear suspension

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Front Suspension System Types

• suspension pivot points, springs & shocks can be arranged in various configurations…

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Short-long arm suspension aka “double wishbone”

• uses upper & lower control arms

• used on many rear-drive domestic cars

• equal length arms would cause tires to scrub across the road

Coilover suspension

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Twin I-Beam suspension

• rugged construction, high unsprung weight

sprung weight: everything supported by the spring

unsprung weight: everything below the spring

used on many Ford trucks

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MacPherson strut

• compact, light, low unsprung weight

• very popular suspension design

• used with unibody construction

• modified strut

used by Ford

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Torsion Bar suspension

• one end fixed to the frame or body structure

• other end fits into the lower control arm

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

position

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

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• torsion bar suspension…

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Multi-link Suspension

• variation of the double wishbone suspension

• each arm of the wishbone can pivot independently

• helps to keep the tire tread planted on the road

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Rear Suspension System Types

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Solid Axle Suspension

• may utilize one of the following spring arrangements…

• coil springs with control arms (figs. a & b)

pan hard bar prevents left-to-right axle movement

what happens to one tire is transmitted to the other tire

• leaf springs suspension (figs. c & d)

a d

c

b

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Solid Axle Suspension• air spring suspension

lighter than a coil spring = lower unsprung weight

no friction

has also been used on front suspension

used on transit and tour buses and many semi trailers

Air Spring Suspension

• read warnings in Mitchell/AllData before servicing vehicles with air suspension

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Semi-Independent

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

• used with MacPherson struts

used on some front wheel drive vehicles

improved ride & handling over solid axle suspension

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Independent – Trailing Arm Suspension

• no tire scrubbing – arms positioned front to back

• takes up a lot of space

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Independent Long-Short Arm Suspension

• short-long arm suspension with coilovers

used on some rear drive performance vehicles

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Suspension System Repair

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Shocks

check for oil leaks

bounce test car on the ground

should bounce once or twice, then stop

age of vehicle & # of km?

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Sway Bar Bushings

• check sway bar mount bushings & outer link kits for wear

worn bushings will lead to clunking noises

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Testing Ball Joints• check ball joint sockets for wear

follow specific inspection procedure in Mitchell

does the vehicle have lower joint only or upper & lower?

they can break & cause tire to “kick out”

leads to loss of control & vehicle damage

• when replacing ball joints, they can be…

threaded into the control arm

pressed into the control arm

riveted to the control arm

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Testing Ball Joints - examples

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Testing Ball Joints - examples

• if the ball joint is disconnected from the control arm, move the ball stud by hand…

should not move easily or feel sloppy

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Control Arm & Strut Rod Bushings

• visually inspect bushings for deterioration

• use a pry bar to check for looseness

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Broken Springs

• coils, leafs or torsion bars that are weak or broken will cause the vehicle to sag on the affected corner

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Removing/Replacing Springs

follow proper spring removal procedures!

use proper spring compressors

spring’s stored energy can injure or kill!

Compressing McPherson Strut Springs

• NEVER loosen/remove the nut at the top of the strut until spring tension has been

released by the coil spring compressor!!!

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

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require your students to call you over before the nut is removed