Tyre Wear
Analysis of tyre wear conditions varies according to the type, size and brand of the tyre fitted to the vehicle. Refer to the tyre manufacturer's literature relating to tyre wear when evaluating tyre wear conditions.
Tyre and Wheel Inspection
This visual inspection should be conducted for all vibration concerns unless the disturbance only occurs with the vehicle at a standstill.
| • | The tyres should be inspected for unusual wear. Unusual wear conditions can cause tyre growl, howl, slapping noises, and vibrations throughout the vehicle. Refer to Tire Diagnosis - Irregular or Premature Wear . |
| • | Check for debris build-up, such as packed mud, undercoating, ice/snow buildup, road tar, etc. If debris build up is found it must be removed. |
| • | Check for bulging in the tyre sidewalls. If bulging is found tyre must be replaced. Refer to Tire Dismounting and Mounting . |
| • | Check the condition of all wheels. Refer to Replacement Wheels Description . |
| • | Check that all tyres are inflated to the correct pressures prior to any road test. Refer to Tire Inflation Pressure Specifications . |
Road Testing
Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.
There are many potential causes for a vibration condition to be present in a vehicle. It is vital that a thorough road test be conducted to identify the causes for a vibration condition.
Slow Acceleration Test
This test is to identify engine or vehicle speed related conditions. It will be necessary to perform additional tests in order to determine in which category the vibration belongs.
- Slowly accelerate on a smooth level road up to allowable speed.
- Identify a vibration condition that matches the customer's description.
- Note the vehicle speed (km/h) and engine speed (RPM) where the vibration condition occurs.
Follow this test with the neutral coast down test, and the downshift test.
Neutral Coast Down Test
- Accelerate on a smooth level road, to a speed slightly higher than the speed at which the vibration occurs.
- Shift the vehicle into NEUTRAL and coast down through the vibration range. Note if the vibration occurs in NEUTRAL.
If the vibration occurs in NEUTRAL, the vibration is vehicle-speed sensitive eliminating the engine and torque converter as a cause. Depending on the symptoms or frequency, the repair will concentrate on either the tyres and wheels, the propeller shaft or the rear axle.
Downshift Test
- Accelerate on a smooth level road, to the speed at which the vibration condition occurs. Note the engine RPM.
- Decelerate and safely downshift to the next lower gear.
- Operate the vehicle at the previously noted engine RPM.
If the vibration returns at the noted engine RPM, the engine or torque converter is the most probable cause. To confirm these results, repeat this test in lower gears and NEUTRAL.
Steering Input Test
This test is intended to determine how much wheel bearings and other suspension components contribute to a vibration, especially those relating to noises, howl, growl, grinding and roaring.
With the vehicle at the vibration speed drive through slow sweeping turns in both directions.
If the vibration gets worse or goes away, the wheel hubs and tyre tread wear are possible causes.
Standing Start Acceleration
The purpose of this test is to duplicate a vibration known as Take-off-Shudder. A powertrain mount or the exhaust contacting the body may also be a potential cause depending on the symptoms.
- With the vehicle at a complete stop and in gear, remove your foot from the brake.
- Accelerate while checking for vibrations that match the customer's description.
Shudder in the seat or steering wheel under these conditions usually results from incorrect driveline angles. Worn, tight or failed universal joint may also be a cause, and should be inspected first.
Grunting or groaning noises along with a buzzing or roughness in the floor usually points to the vibration being conducted through the engine or transmission mounts, or through exhaust mounts and hangers that have grounded.
