Bearing Howl and Whine

Before disassembling the axle to diagnose and correct gear noise, eliminate the tires, exhaust, trim items, roof racks, axle shafts and rear wheel bearings as possible causes.

The noises listed on the Road Test Form usually have specific causes that can be diagnosed by observation as the unit is disassembled. The initial clues are, of course, the type of noise heard on the road test and the driving conditions.

Bearing malfunctions will normally be obvious at disassembly. As noted earlier, inner and outer pinion bearings make a high-pitched, whistling noise, usually at all speeds. If there is only one pinion bearing that is malfunctioning, the noise may vary in different driving phases.

Pinion bearings are frequently replaced unnecessarily on axles with low mileage (under 24,139 km [15,000 miles]) when correcting gear noise. They should not be replaced unless they are actually scored or damaged, or there is a specific differential pinion bearing noise. Examine the large end of the rollers for wear. If the pinion bearing's original blend radius has worn to a sharp edge, the pinion bearing should be replaced.

Remember that the low-pitched rumble of a worn or damaged wheel bearing can also be caused by the exterior luggage rack or tires.





Rear wheel bearing noise might be mistaken for pinion bearing noise. Inspect the rear wheel bearing carefully before tearing down the axle.

Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by damaged pinion bearings, which are operating at driveshaft speed. Bearing noise occurs at all driving speeds. This distinguishes it from gear whine which usually comes and goes as speed changes.