Bearing Noise Analysis

BEARING WHINE
This 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. However, if there is only one differential pinion bearing that is malfunctioning, the noise may vary in different driving phases.

Differential 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 pinion bearing noise. Examine the large end of the rollers for wear. If the bearing's original blend radius has worn to a sharp edge, the differential pinion bearing should be replaced.

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

Bearing damage will normally be obvious at disassembly. As noted earlier, damaged differential pinion bearings make a high-pitched, whistling noise, usually at all speeds. However, if there is only one pinion bearing that is damaged, 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 bearing original blend radius has worn to a sharp edge the differential pinion bearing should be replaced.

The low-pitched rumble like a damaged bearing can also be caused by tires.





Look at the bearing carefully before tearing down the axle. Check for a (A) spelled cup, (B) spelled roller or (C) damaged rollers. Replace the bearing if any of these concerns are detected.