1990 Other BMW Models differential?

JOE SIWIEC

MEMBER
1990 BMW
6 CYL
2WD
AUTOMATIC
135,000 MILES

I recently had some work done on a 90 735il. This included aotomatic steering box, transmission rebuild, drive shaft bearings, motor mounts, spark plug and spark plug wire replacement. The noise I will describe may have been present in some form prior to the work but I'm not sure. At approximately 30 mph there is a distinct whirring sound especially when descellarating, with or without braking, and also when accellerating. It sounds like an electric motor running at a very high speed. The car runs fine at higher speeds and the repair shop rechecked the tranny and claims it is ok. He suspects rear end or tire problems. In surfing the internet the diagnosis by various entities seems to point to differential gear problems.

1. Can the problem be more accurately diagnosed?

2. What is involved (costs to replace the differential?

Thank you.

2 Replies

MASTERTECHTIM

MECHANIC
4,749 POSTS

Yes it can be properly diagnosed. It sounds as though it may be rear end pinion bearings making the noise as you describe it. There is a tool called a chassis ear that a lot of shops have. This is a magnet that can be put on trnamission and rear end, you then drive vehicle and with earphones you can tune into rear end or trans and determine where the noise is coming from.