Suspension: Testing and Inspection
DIAGNOSIS AND TESTING
Tire Wear
Tires should be inspected as abnormal or excessive wear may be caused by incorrect wheel alignment, wheel/tire imbalance, or incorrect tire pressure.
Vibration and Roughness
Vibration, roughness, and shimmy conditions may be caused by excessive tire or wheel runout, worn or cupped tires, or wheel and tire unbalance.
Most of these conditions are due to irregularities in the road surface, hence driving the vehicle on different types of road surface will often indicate the cause of the condition.
Do not automatically suspect the tires when attempting to diagnose a vibration concern as other sources of vibration may include:
^ Loose or worn wheel bearings.
^ Loose or worn suspensions or steering components.
^ Worn or damaged drive shaft.
^ Front disc rotor runout (only when braking).
^ Loose engine or transmission supports.
^ Engine driven accessories,
^ Driveline alignment.
Before investigating any other vibration concerns, a road test and a customer interview (if possible) should be carried out. This can provide much of the information needed to find the source of vibration.
Drive the vehicle on a road that is preferably smooth and free of undulation and if vibration is apparent note, the speed at which the vibration occurs, what type of vibration that occurs in each speed range (mechanical or audible), how the vibration is affected by changes in vehicle speed ,engine speed and engine torque, and the type of vibration sensitivity (torque sensitive, vehicle speed sensitive, or engine speed sensitive).
Some of the condition terms used when describing sources of vibration are explained as follows:
^ Torque Sensitive
- This condition can be improved or worsened by accelerating, decelerating, coasting, maintaining a steady vehicle speed and application of engine torque.
^ Vehicle Speed Sensitive
- This means that the vibration always occurs at the same vehicle speed and is not affected by engine torque, engine rpm, or transmission gear selection.
^ Engine Speed Sensitive
- This means that the vibration always occurs at varying vehicle speeds when a different transmission gear is selected.
- It can sometimes be isolated by increasing or decreasing engine speed with the transmission in 'NEUTRAL', or by stall testing with the engine in gear. If the condition is engine-sensitive, the condition is not related to tires.
- If the road test indicates that the vibration is related to the tires or wheels, use a 'Tire Wear Diagnosis Chart' to investigate the cause of concern. Should the road test indicate that there is tire whine, but no shake or vibration, the noise originates from the contact between the tire and the road surface.
Front End Inspection
Do not check and adjust front wheel alignment without carrying out the following inspection for front end damage and wear:
^ Check for specified air pressure in all four tires.
^ Raise front of vehicle off the floor; check front wheel bearings for excessive endfloat.
^ Check front suspension lower arm ball joint and mounts for looseness, wear and damage.
^ Check brake caliper mountings.
^ Check steering gear mountings and all steering linkages for looseness.
^ Renew parts if necessary.
^ Grasp upper and lower surface of tire and shake each wheel to check wheel bearing end play.
^ Check the action of the front dampers and the condition of their attachments, as sticking or binding front dampers may not allow the vehicle to settle in to a normal level position, possibly affecting the front-wheel alignment.
Note: Front wheel bearings are adjustable (0.001 to 0.003 in. endfloat).
Upper / Lower Ball Joint Inspection
^ Check the wheel bearings.
^ Inspect the front suspension upper joint and renew front suspension lower wishbone if needed.
^ Raise vehicle and position floor jacks beneath the front suspension lower wishbone.
^ Grasp the lower edge of the tire and move the wheel in and out.
^ While moving the wheel, observe the upper and lower wishbone.
^ Movement between the vertical links and the wishbones indicates abnormal ball joint wear.
^ Renew ball joints.
^ Check the front wheel bearings.
^ Check for excessive play and wear.
Damper Inspection
Note: The gas-pressurized hydraulic front dampers are not serviceable, adjustable or refillable.
^ Verify that all attachments of the suspension components and the front dampers are tight. Renew any front damper that has a damaged integral lower mounting bushing.
^ Check front dampers for external damage.
^ Check for oil leakage and vehicle sag.
- Oil Leak
Leakage is the condition in which the entire damper body is covered with oil and from where it will drip on to the pavement. Due to correct damper lubrication a light film of oil (weepage) can usually be seen on the upper portion of the damper.
Should there be any leakage, ensure that the fluid does not originate from sources other than the front damper. Renew worn or damaged dampers.
- Vehicle Sag
Renewing front dampers will not correct the problem of vehicle sag, as basically this is controlled by the spring units.
Rear Suspension Inspection
^ Check for evidence of fluid leaks from rear dampers.
^ Check damper operation.
^ Check condition of lower wishbone / pendulum, subframe bushes and rear suspension strut bushings.
^ Renew damaged or worn components.
Vehicle Inspection
^ Check all tires for correct inflation pressure.
^ Check tire condition to confirm correct front end alignment,tire balance and overall tire conditions such as separation or bulges.
^ Check the vehicle attitude for evidence of possible overload or sagging.
^ Check luggage compartment area.
^ Road test vehicle to confirm customer's concern.
Diagnostic Procedure
Chart
Chart (continued)