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BMW Differential vs. Wheel Bearing Noise

October 27, 2010

This answer is applicable for many BMWs in addition to the one listed below.

Q
car year: 1999
car model: 323is
My Bimmer started to make this whining/puddering sound, almost sounds like a wheel bearing. The noise increases with rpm and seems to get louder and more noticeable under heavy load, i.e downshifting and letting the gear slow down the vehicle. I had a driveshaft center support bearing installed, but nothing changed. I did notice some small metal flakes in the rear differential fluid so I changed the oil, still makes the sound. Do you think this could be a bad differential? Any other ideas would be greatly appreciated!

A
The way you’ve described the noise that you’re experiencing makes us think that it is from the differential.  Either bearing noise or gear noise.  A differential will make a whirring, whining or growling noise if one of the bearings is worn or the ring and pinion gears are worn or meshing improperly.  Similar to a wheel bearing, the noise will change with vehicle speed.  However, a wheel bearing noise will not change with slight changes in load (slight throttle on/off changes, coasting versus accelerating, etc.).   Additionally, a differential noise will typically not change as you turn right or left (loading the vehicle to one side or the other), as a wheel bearing can do.   Note that this only applies to independent suspension designs.  A “live axle” design (such as many domestic rear-wheel drive applications) could also change it’s noise when side loaded, if the gears or bearings are faulty.

In reality, a bad differential bearing or gear set is not really something that you would repair yourself.  This requires that the differential either be rebuilt or replaced.  A used replacement unit is likely your lowest cost alternative.

In the case of a failing wheel bearing, Bavarian Autosport stocks the bearings and the tool required to perform the bearing replacement.   See the link below for a blog post containing additional information on BMW rear wheel bearings.

Click HERE for additional rear wheel bearing information

We also have a complete DIY on replacing rear wheel bearings, using the B90-BMW wheel bearing tool.

Click HERE for rear wheel bearing replacement DIY

Rear wheel bearings:

Wheel bearing tool:

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