Rebuild rear Differential

[albundy]

I almost bought the bearings for this rebuilding exercise until my mechanic mentioned that it could be the pinion gears. It is possible for the pinion gears to wear out?? My differential hums from 50-55mph. Its relatively quiet at other speed.

Thanks

Don w

[bill g]

The pinion gear meshes with the crown wheel (a large gear) - it is possible for either or both to be worn, or they could be incorrectly adjusted which causes gear whine. The adjustment or setting is affected by wear in the gears. Worn bearings can make their own noise but also the worn and loose bearings can upset the meshing of the gear teeth causing gear whine. The crown wheel and pinion come as a matched pair, carefully chosen to work together properly without excessive noise - they would have to be badly worn or have broken teeth to need to be replaced. There is a fair bit of science to this - diffs require extreme cleaniliness and care in setting up.
You really need technical diagrams and specifications for set up - I have not been able to find any specifically for the BMW diff.