Non-Axle Noise

There are a few other conditions that can sound just like axle noise and have to be considered while performing road test diagnosis. The five most common are transmission, exhaust, tires, roof racks and trim mouldings.

Therefore, ensure that none of the following conditions are the cause of the noise before proceeding with an axle teardown and diagnosis.

1. In certain conditions, the pitch of the exhaust may sound very much like gear whines. At other times, it can be mistaken for a wheel bearing rumble.

2. Tires, especially snow tires, can have a high-pitched tread whine or roar, similar to gear noise. Radial tires, to some degree, have this characteristic. Also, any non-standard tire with an unusual tread construction may emit a roar or whine-type noise.

3. Trim and mouldings can also cause whistling or whining noise.

4. Clunk may be a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE, or it may occur when throttle is applied or released. It is caused by backlash somewhere in the driveline; it is felt or heard in the axle. Refer to Clunk Diagnosis.

5. Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by malfunctioning pinion bearings, which are operating at driveshaft speed. Roller wheel bearings may whine the same way if they run completely dry. Bearing noise occurs at all driving speeds; this distinguishes it from gear whine, which usually comes and goes as speed changes.

6. Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a malfunctioning wheel bearing. The lower pitch is because the wheel bearing turns at only about one-third of driveshaft speed.

7. Bearing noise. Wheel bearing noise might be mistaken for pinion bearing noise, so always look at the wheel bearings carefully before tearing down the axle. As noted earlier, pinion bearings make a high-pitched, whistling noise, usually at all speeds. However, if there is only one pinion bearing that is malfunctioning, the noise may vary in different driving phases. If a pinion bearing is suspected, refer to Group 05 for service procedures. Bearings should not be replaced unless they are actually scored or damaged.
   
   
   
   

   Rear wheel bearings are pressed into the axle housing, making it more difficult to check them. However, the axle shaft is the inner race for the bearing. So if the bearing is damaged, the roller surface on the shaft will be damaged as well. The rollers run on about the center of the polished surface.