Flow of Diagnosis

DESCRIPTION
Certain rear axle and driveline concerns are also common to the engine, transmission, wheel bearings, tires and other parts of the vehicle. For this reason, make sure the cause of the trouble is in the rear axle before adjusting, servicing or replacing any of the parts.

Rear axle concerns can be diagnosed and corrected quickly by following the proper procedures. Being able to perform a good diagnosis is necessary in order to eliminate guesswork and save time.

This section defines various possible rear axle conditions and tests for identification of cause and service procedure. The four rear axle conditions that will be reviewed are:
1. Leakage Conditions
2. Vibration Conditions
3. Noise Conditions
4. Inoperative Conditions
The diagnostic material also deals with symptom analysis, which discovers the original cause so repeat service can be avoided. However, the purpose of this section is to provide information on service steps of special importance.

NOISE ACCEPTABILITY
A gear-driven unit, especially an automotive axle, will produce a certain amount of noise. Some noise is acceptable and may be audible at certain speeds or under various driving conditions such as a newly paver blacktop road. The slight noise is not detrimental to operation of the rear axle and must be considered normal.

QUESTION THE CUSTOMER
The preliminary diagnosis begins with the service technician asking the customer enough diagnostic questions, especially for conditions of noisy operation and vibration. Always ask the customer about:
^ The exact nature of the symptom. If it is a vibration, how is it felt? If a noise, what kind? Is it high-pitched, a rumbling noise or some other concern?
^ The driving conditions in which the symptoms occur: road speed, drive or coast, on turns or on a grade only.
^ Whether the condition is constant or variable: does a noise increase in pitch with speed or some other factor?
^ Have the customer demonstrate the symptoms on a road test whenever possible.

AXLE DIAGNOSIS CHECK SHEET
If there is enough reason to suspect an axle concern, the service technician should also initiate an NVH Road Test Form. NVH Check Sheet