Noise, Vibration and Harshness

A gear-driven unit, especially an automotive drive axle, will produce a certain amount of noise. Some noise is acceptable and may be audible at certain speeds or under various driving conditions, as on a newly paved blacktop road. The slight noise is in no way detrimental to the operation of the rear axle and must be considered normal. Camshaft belt whine is most often associated with new belts used on smaller engines. Whine will usually go away after belt break-in.

NOTE: It is important that the rear axle noise on vehicles equipped with either a manual or automatic overdrive transmission be evaluated in direct drive rather than overdrive.

The road test and customer interview (if available) provides information needed to identify the condition and give direction to the correct starting point for diagnosis.

1. Make notes throughout diagnosis routine. Use a Road Test form that includes space for comments. Make sure to write down even the smallest bit of information it may turn out to be the most important.

2. Road test the vehicle and define the condition by reproducing it several times during the road test.

3. Perform the Road Test Quick Checks as soon as the condition is reproduced. This will identify the proper section of the diagnosis procedure. Run through the quick checks more than once to ensure they are providing a usable result. Remember, the Road Test Quick Checks may not tell where the concern is, but they will tell where it is not.

4. Do not touch anything until a road test and a thorough visual inspection of the vehicle have been performed. Leave the tire pressures and vehicle load just where they were when the condition was first observed. Adjusting tire pressures, vehicle load, or making other adjustments, may reduce the condition's intensity to a point where it cannot be identified clearly. It may also inject something new into the system preventing proper diagnosis.

   Make a visual inspection as part of the preliminary diagnosis routine, writing down anything that does not look right. Note tire pressures, but do not adjust them yet. Note leaking fluids, loose nuts and/or bolts, or bright spots where components may be rubbing against each other. Check the luggage compartment or cargo area for unusual loads.