For 1990-2009 cars

The most essential part of rear axle service is proper diagnosis of the problem. In axle work, one of the most difficult areas to diagnose is noise. Any gear driven unit, especially a gear driven axle where engine torque occurs at a 90 degree angle, produces a certain amount of noise. An interpretation should be made for each vehicle to determine whether a noise is normal of if a problem actually exists. One way of determining this is road testing an identical vehicle with the same options under the same conditions. If the same amount of noise is audible at the same speeds and under the same conditions, it may be deemed commercially acceptable since it is unlikely that the exact same problem exists in both vehicles. A normal amount of noise must be expected and cannot be eliminated by conventional repairs or adjustments. However, if a noise proves to be extremely loud or unusual, then it should be investigated. This can be accomplished by a road test and a systematic check of the components associated with the rear axle to isolate the noise.

### Preliminary Checks

In order to perform an accurate road test, it is important that certain checks be performed to eliminate other possible problems that may point to the front axle. Make sure to check the following items before performing a road test.

• | Inspect the tires for correct inflation pressure. Refer to the Tire Placard on the drivers door lock pillar.

• | Inspect the rear axle housing for correct oil level. Refer to Lubricant Level Check in Front Drive Axle.

• | Inspect the undercarriage for loose attaching rear axle parts which may cause noise.

• | Inspect the rear suspension for any loose or worn components.

#### Road Test

When road testing a vehicle, a smooth asphalt road surface is preferable because it dampens a high degree of road noise. Road test the vehicle to verify the problem and the speed and/or rpm at which it occurs. Once the problem has been verified, duplicate the noise under varying road conditions to eliminate the possibility of road noise. Once the noise and the conditions under which it exists have been verified, the type of noise and its location must be identified.