Preliminary Diagnosis

Question the Customer

The preliminary diagnosis starts with the customer interview. The history of the concern must be investigated: When was it first noticed? Did it appear suddenly or gradually? Did any abnormal occurrence coincide with or precede its appearance (such as pothole or curb impacts, minor collisions, etc.)? Were any repair procedures carried out or new parts installed? It is also necessary to know any special conditions affecting the appearance and degree of the concern, such as road speed, type of road, drive mode, engine temperature, ambient temperature, etc.
A gradual appearance of the concern indicates a deterioration of a component, such as tires, halfshafts or wheel bearings.
A sudden appearance of the concern could indicate a lost wheel balance weight or seized Constant Velocity (CV) joint.

Road Test





Vehicle Road Test Evaluation Form

A road test is mandatory for any customer concern of noise/vibration that is not verified by the on-hoist check of chassis components. The Vehicle Road Test Evaluation form is arranged to record the conditions heard or felt during this test.








The road test form lists four operating conditions or modes in which some axle noises come and go: DRIVE, CRUISE, COAST, and FLOAT.
Operate the vehicle in all four modes and record those in which the noise occurs. Write down the kilometers-per-hour (miles-per-hour) range at which both noise and vibration occur. Evaluate rear axle noise with the transmission in DIRECT DRIVE and not in OVERDRIVE. Transmission noise can be mistaken for rear axle noise when in OVERDRIVE.