Do I need a diff rebuild?

[Lee_Enfield]

I've had my 2002 M3 with 224k km for about a year now, and have noticed there is a very high pitched whine comeing from the rear. Ibest way to describe it is it sounds like running your finger around a wine glass. Very high pitch.

It's not a constant tone, mostly present above 80km and usually only when cruising under light load, or decelerating. Not present under load when accelerating.

Thought it was wheel bearings, bearing showed a little play so did both sides, still there. Changed the diff oil with BMW fluid with the friction modifier, no change.

So, I am thinking the bearings in the diff are on the way out. So, three questions.

One, do people agree that the diff needs a refresh?

Two, what are the best places to get bearings? I was thinking racingdiffs kit, but could probably save a bit buying buying the bearing seperate from a bearing supplier and the seals from a parts supplier. Which leads to question three,

What are the koyo part numbers for the bearings?

Thanks.

[sapote]

It's not a constant tone, mostly present above 80km and usually only when cruising under light load, or decelerating. Not present under load when accelerating..

Get to 80Km then shift to neutral and see if the noise change. I agree the noise is not wheel bearings as if it is then it should be a constant noise independence of throttling.
This high pitch noise doesn't sound like form diff ring/pinion which normally is a howling noise. Get down under and look for heatshield loose heatshield metal sheet.

[Lee_Enfield]

I was under there during the winter and didn't notice any loose shielding.

I'll have another listen later, play around with the power settings and see what I hear.

[Lee_Enfield]

Well, did some driving.

So, at low speed there is a shine that sounds like a gear whine, as I speed up its gets higher pitch, starts to sound more like a hydraulic pump whine at around 80, and as you get faster it starts to sound like whistling/ the wine glass ring.

Mostly when decelerating or coasting but noticed it a few times under power now. Noise stays when clutch is pressed, depending on the grade/speed.

Its slowly getting more noticeable so something is definitely going.

[Da Jemster]

Mine sounded like my rear pads were in constant contact with the rotor - high squeal. It was my diff and it had to be rebuilt.

[ac427]

Check the torque required to turn the diff input shaft, this will give you a good indication of whether the lash between the pinion and crown wheel is correct.

Has the input seal been replaced at all?

[Lee_Enfield]

Apart from fluid change, I do not know what was done to the diff.

I am leaning towards doing a rebuild regardless, car has 225k km and I would out money on it not being done ever.

[sapote]

Noise stays when clutch is pressed, depending on the grade/speed.

Test again but shift to neutral instead of just disengage the clutch, as in neutral the input gear train doesn't rotate.

The diff should not have the high pitch noise of wine glass/finger nail.

[Lee_Enfield]

Played around again, seems to stay even in neutral.

[sapote]

Played around again, seems to stay even in neutral.

Then it's not the tranny noise.

[Lee_Enfield]

OK, so I would assume diff?, its definitely coming from the rear of the car.

What are the Koyo part numbers for the bearings and races? Also, if I replace the clutch pack as well, do I need to re shim? I might just replace the bearings and seals if I do.

[Arith2]

Sounds like a failing diff. When you drained the fluid, was it grey?

[Lee_Enfield]

Sounds like a failing diff. When you drained the fluid, was it grey?

Cant remember the color. It was a very dark, nearly black is all I remember. I was last year when I did it.

[sapote]

OK, so I would assume diff?, its definitely coming from the rear of the car..

I still don't see a reason why a diff ring/pinion can cause such high pitch noise. I still believe it is outside of tranny and diff.
Do this: shift to neutral, turn the main drive shaft to find the total backlash before it moves the wheel. How much rotation of the backlash?

[bigjae46]

Could also be the spider gears in the diff housing. Or the clutch discs spinning against the steels. At 224k miles it's probably worth a full rebuild. I just rebuilt the diff in my buddy's car...huge difference. It was pretty much an open diff.

I use Timken bearings and races with OE seals.