1986 325 whirring noise from rear - differential questions

[paulmess]

Hello,

Unfortunately my e30 with only 99k miles developed a whirring noise from the rear. It sure sounds like the differential to me, although I'm no expert. It's gradually getting worse too. I changed the fluid, no metal shavings or change in the noise.

From my research it looks like an 86 325 has a 2.93 rear. Nobody local is selling one. Are there any other ratios that I can consider? Assuming it's just a bolt in swap.

Also do we have any members in the Denver area that could help me diagnose the issue? I'm really thinking it's the differential but before I purchase parts I would love a second opinion.

Thank you,
Paul

[TobyB]

If the original fluid looked good,
did you check the center bearing?
They can sound like diff input bearings.
Also, try taking the backseat out and driving around.
If it's the diff, it will get way louder...
Have you looked at the rear diff bushing?
hth,
t

[paulmess]

If the original fluid looked good,
did you check the center bearing?
They can sound like diff input bearings.
Also, try taking the backseat out and driving around.
If it's the diff, it will get way louder...
Have you looked at the rear diff bushing?
hth,
t

I just had the backseat out to replace the fuel pump and it definitely got louder! Interesting suggestion on the center bearing. If i give the driveshaft a shake with my hand could I feel play if it was bad?

[TobyB]

Not if it's just getting noisy- you'd probably have to pull the driveshaft and feel how
it spins.

My other thought on that was that the center bearing seems to suffer the effects of age
worse than the diff- as in, on a 100k car, I'd be shocked if a well- maintained diff died,
but on a 30 year old car, a new center bearing seems pretty normal.

hth
t

[paulmess]

Not if it's just getting noisy- you'd probably have to pull the driveshaft and feel how
it spins.

My other thought on that was that the center bearing seems to suffer the effects of age
worse than the diff- as in, on a 100k car, I'd be shocked if a well- maintained diff died,
but on a 30 year old car, a new center bearing seems pretty normal.

hth
t

How difficult is it to replace a center bearing? If I pull the driveshaft and decide the center bearing is the culprit, would it be significantly easier to replace it with a driveshaft from another e30?

[TobyB]

If you can get the driveshaft off, changing the bearing's not going to be difficult for you.
Mark the shaft alignment, loosen the nut, slide it apart, thump the old one off,
gently tap the new one on, reassemble. A piece of pipe just a little larger than the OD of
the splines makes it easy to be gentle. I have had luck with plastic pipe- some don't.

And it's cheap- hope it's your problem...

t

[packratbimmer]

Check out the rear subframe bushings. The differential will be on a bind if they are shot.