Suspension System Diagnosis and Repair

Contents Suspension system diagnosis Shock absorber service (8 Topics) Suspension system diagnosis Shock absorber service Suspension spring service Ball Joint service

Contents Suspension bushing service MacPherson strut service Wheel alignment is needed Computerized suspension diagnosis

Suspension System Diagnosis Symptoms of suspension system problems: abnormal noises tire wear steering wheel pull front end shimmy

Diagnosing the Suspension System Gather information from the customer or service writer Inspect the parts that could cause the problems indicated If necessary, road test the vehicle to verify the complaint

Suspension System Problems

Front Suspension System

Shock Absorber Service Worn shock absorbers will cause a vehicle to ride poorly When the tire strikes a bump, a bad shock will not dampen spring oscillations Loose or damaged shock absorbers may produce a loud clanking noise as the loose parts bang against the body

Checking Shock Absorber Condition Perform a visual inspection for damage, rubber bushing wear or oil leakage Perform a shock absorber bounce test push down on one corner of the vehicle release the body count the number of times the body rebounds maximum two or three oscillations

Replacing the Shocks Raise the vehicle on a lift Remove the wheels Support the control arms or axle housing with a jack or jack stand Remove the old shock absorbers Install the new shock Install the wheels and torque to specs

Replacing the Shocks Support the control arm to prevent the spring from forcing parts down violently

Unbolting the top and bottom of the shock Replacing the Shocks Unbolting the top and bottom of the shock

Air- and Gas-Charged Shock Service Gas-filled shocks require replacement when faulty Air shocks may be repairable Air leakage may occur at air lines, an air valve, or the shocks themselves To test, wipe on a soap-and-water solution, watching for bubbles that indicate leakage

Suspension Spring Service Spring fatigue allows a vehicle’s body to settle, lowering the curb height changes control arm position misalignment results Fatigue can occur after prolonged service

Measuring Curb Height Place the vehicle on a level surface Measure from a specified point on the frame, body, or suspension down to the floor Compare the distance to specifications If the curb height is too low, spring replacement or torsion bar adjustment will be necessary

Curb Weight Weight of the vehicle with a full tank of fuel and no passengers or luggage Vehicle should be at curb weight when measuring curb height remove everything from the trunk except the spare tire and jack

Coil Spring Compressor Squeezes the coils closer together. Reduces the length of the spring

Coil Spring Compressor Coil spring compressor kit

Coil Spring Removal Raise the vehicle on a lift Support the control arm or axle housing Remove the shock absorber Install the spring compressor and compress the spring

Coil Spring Removal If necessary, separate the lower or upper ball joint using a separator tool

Coil Spring Removal Remove any components that could be damaged when the control arm is lowered: brake line, strut rod, steering linkage Pull the spring and the compressor out as a unit

Coil Spring Installation Compress the new spring Slip the spring into place and position the coil ends in the same location as the old spring Reassemble the ball joint and other components Unscrew the spring compressor while guiding the coil into place Install the wheels and lower the vehicle

Rear Coil Springs Lower the axle after unbolting the shocks– the coils will simply fall out

Leaf Spring Service Service usually involves spring or bushing replacement Place jack stands under the frame Use a floor jack to raise the weight of the rear axle off the leaf spring Remove the U-bolts that clamp around the middle of the spring and the axle

Leaf Spring Service Slide the through-bolts out of the spring Remove the old leaf spring Install the new leaf spring Reassemble and lower the vehicle

Spring Bushing Replacement Replacing a worn bushing with a driving tool

Torsion Bar Service Most torsion bars are adjustable Replacement is not generally needed unless a torsion bar breaks When curb height is too low, tension must be increased to raise the vehicle

Torsion Bar Suspension

Ball Joint Service Worn ball joints cause the steering knuckle and wheel assembly to be loose on the control arms Clunking or popping sounds might be heard when turning or driving over bumps

Ball Joint Lubrication Wear is usually a result of improper lubrication or prolonged use If dry, the joints can wear out quickly Grease fittings or lube plugs may be provided lubricate joints with a grease gun at regular intervals Many late model ball joints are sealed units that do not require lubrication

Ball Joint Lubrication Replace lube plugs with grease fittings

Ball Joint Lubrication Grease the ball joints and any other fittings provided regularly Only install enough grease to fill the boot

Checking Ball Joint Wear Two methods of checking ball joint condition are commonly used: ball joint wear indicator measure the play in the ball joint

Ball Joint Wear Indicator Part of the ball joint Inspect when the weight of the vehicle is on the wheels A shoulder around the grease fitting will recede into the joint as it wears When the shoulder recedes below the surface, replace the joint

Ball Joint Wear Indicator

Measuring Ball Joint Play Jack up the vehicle weight must be removed from the joint Physically move the control arm and tire assembly Use a pry bar, watching for joint movement Compare movement to specifications

Measuring Ball Joint Play Lift points for different suspension systems

Measuring Ball Joint Play

Ball Joint Removal Raise the vehicle on a lift Support the control arm Remove the shock absorber Install a coil spring compressor on the spring if necessary Remove the nut securing the ball joint to the steering knuckle Separate the knuckle from the joint

Ball Joint Replacement (Press-fit) Remove and install ball joint using a ball joint driver

Ball Joint Replacement (Riveted) Drill out the rivet heads Drive out the old rivets Bolt on the new ball joint

Ball Joint Replacement If the ball joint is screwed into place, use a large wrench to unscrew the old ball joint Clean the threads in the control arm Torque the new joint to specifications Reassemble the vehicle Remove the spring compressor if used Lower the vehicle

Suspension Bushing Service Rubber bushings are commonly used on the inner ends of the control arms Bushings should be checked periodically for wear Worn bushings can let the control arms move sideways, causing tire wear and steering problems

Checking Bushing Wear Try to move the control arm against normal movement Watch the bushings If the arm moves in relation to its shaft, the bushings are worn and must be replaced

Bushing Removal Procedures vary, refer to a service manual Stabilizer bar and strut rod must be unbolted from the control arm Remove bolts passing through the bushings Remove the control arm Bushings are pressed or screwed into the control arm

Bushing Removal

Using a driver on a pressed-in bushing Bushing Replacement Using a driver on a pressed-in bushing

Bushing Replacement With this design, nuts are used to force new bushings into the control arm

Bushing Replacement Reinstall the control arm Torque all bolts properly Install the ball joint cotter pin and other components Bushings may require preload with the weight of the vehicle on the wheels lower the vehicle before tightening control arm shaft nuts

MacPherson Strut Service The most common problem is worn strut shock absorbers seals inside the strut can begin to leak damping is reduced vehicle ride is affected

Strut Removal

Remove the strut as a single unit. Note the alignment for reassembly Strut Removal Remove the strut as a single unit. Note the alignment for reassembly

Strut Disassembly Use a spring compressor to remove the coil spring After the spring is squeezed together, remove the upper mount assembly Release spring tension and lift the spring off the strut Inspect the parts for wear and bearing roughness Replace parts as necessary

Spring Compressors Portable Bench-mounted

Strut Assembly Inspection

Replacing a Strut Cartridge

Assembling the Strut Fit the strut into the compressor Compress the spring Install the upper spring seat and mount assembly Release the spring compressor

Strut Assembly

Strut Installation Lift the strut into position in the upper body mount Attach the lower end of the strut to the steering knuckle or bearing support Align any reference marks Install the fasteners Install any other parts

Always torque fasteners to specs Strut Installation Always torque fasteners to specs

When Alignment is Needed After servicing ball joints, control arm bushings, strut rods, springs, strut assemblies, or other suspension parts, wheel alignment must be checked and adjusted Rapid tire wear or handling problems could occur if alignment is altered

Computerized Suspension Diagnosis

Computerized Suspension System

System Diagnosis Connect a scan tool to the diagnostic connector Read any stored diagnostic trouble codes Check scan data for suspension-related operating values If any problems are noted, use pinpoint checks to isolate the source of the problem

Scan Tool Display A. Select the desired control module B. Choose a mode such as read codes C. Trouble code display

Scoping the output signal from a height sensor Pinpoint Tests Scoping the output signal from a height sensor

Pinpoint Tests Voltage waveform from a height sensor. Voltage should rise and fall smoothly as the arm is moved

Height Sensor Service Sensor can fail mechanically due to worn parts, a bent arm, or broken parts Sensor may also fail electrically, ceasing to produce a normal signal Replacement is usually required

Height Sensor Replacement

Compressor Service A faulty compressor will not produce the air pressure needed to maintain the correct ride height Check the electrical connections and source voltage Connect a pressure gauge to the output hose fitting to measure pressure output If the pressure is not within specs, replace the compressor

Compressor Replacement

Electronically-Controlled Shock Service When replacing the shocks, you may be able to transfer some of the electronic parts from the old units onto the new ones Do not install conventional shocks to save the customer money constant trouble codes might be set and vehicle safety could be adversely affected