Diff noise?

[SHunter]

I have an m52 swapped car with a zf320 trans and 3.15 torsen diff out of a z3. I'm getting a whining sound from the rear of the car that is most noticeable at 55-65mph. It doesn't change pitch at all with speed but the volume is greatly effected by load, being most noticeable at very slight throttle. The sound goes away completely off-throttle and is hardly noticeable at even half throttle. It is pretty annoying to me when cruising on a smooth freeway.

I first noticed it after installing new subframe bushings and tires a couple of months ago. I don't think this caused the problem but rather uncovered it since my car is much quieter now with new tread and firm bushings.

Since then I have also installed and aligned a new driveshaft which made no difference at all in this particular noise but fixed my slight vibration when accelerating and quieted the car down further when cruising. The old driveshaft had a stiff u-joint but it wasn't too bad actually.

To diagnose this problem I've checked for play in the wheel bearings even though it doesn't really have the same grumble. I've also squeezed a bunch of fresh CV grease into the axle joints hoping for a change in the sound.

Fluid in the trans and diff is about 1yr old and so is the diff bushing(although it is a softy rubber bushing from a z3.)

I'm thinking differential output bearings because of the load sensitivity but I'm really not sure. Any other ideas? Anybody rebuilding these things? I have limited access to a large press but I'm not sure I want to get into re-shimming and preloading the bearings.

SH

[jlevie]

The differential bearings could be bad, but noise from the output bearings should not change under deceleration. Worn pinion bearings will change the pinion to ring gear depth clearance. That or wear in the output shaft bearings, that changes ring to pinion free play will cause a noise that is torque direction sensitive.

Get the car up on a lift, have someone drive it, while a pro listens to the noise. My guess is that the differential needs to be rebuilt.

[Wanganstyle]

Whining that is load input related is often pinion bearings and races dying.


You can rebuild the current unit and properly reset its bearing preload/gear mesh relationship or simply remove and replace with a known good used unit.

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