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.
