what's that clunking caused by play somewhere in driveline?

[static]

Hi

really sorry for the lengthy post, but please bear with me and give me an advice/solution

Resently i had a S50 swapped in my e30 (i hired a good BMW mechanic to do it for me). It's mostly great but there are weird noises that i want to get to the bottom of.

One of the most annoying is a muffled metal-to-metal clunk that comes out from middle-rear of the car when i upshift and reengage the clutch or i can basically reproduce that clunk the folowing way: shift to the first and as i drive very slow 2-3rpm in first, keep bliping the throttle on and off, on and off and so on (and off :) - so, on each "on" or "off" there is a thrust in a driveline which causes it to clunk. I suspected that it could be play somewhere in the driveline, so i more or less localized it to driveshaft and LSD (mine is 3.25 with unknown history, but i serviced it - changed bearing, seals and fluid - they also said that whatever they saw under the cover looks good)
Also everything is bolted up properly, and no nuts/bolts are loose

So i figured that it could be one of three things:
- driveshaft (mated e36m3 front half-shaft with a 325i e30 rear-half shaft), new center bearing
- LSD (hope it's not that)
- halfshafts/CV joints (have not been replaced)

any plausible guesses are welcome

also there is another symptom: if i jack up only one rear corner and put the car in speed, i try to spin the wheel back and forth but it has about a 1-2 degree play before the Limited Slip catches up and not let it spin further (since the other rear corner is on the ground.) so basically one axel has a 1-2 degree play, however i also noticed that this 1-2 degree play also transmits to the driveshaft (but not to the other axel as i mentioned)
- is that normal for an LSD? or could that be the source of the clunk?

Thanks a lot everyone
Alex

[Erick]

I destroyed my 3.25LSD because I was unaware of a leak it had through it's output shafts. Not where you pop them in, but right at the diff casing itself. Both sides were leaking and I did not notice in time to do something about it.

What resulted was a horrible clunk whenever you did a turn that you could remotely consider sharp. It made a 250mile trip home like that (straight line for the most part), but I tried driving it once more after that and the car barely made it to the gate.

- Erick

[sweetride01]

I get the same clunk in my car (M20 3.73). My diff is really on its way out, so it could easily be the diff. I have never had the problem specifically diagnosed, but I think that it's probably the diff giving you the problem.

[JJ Byzanz]

Could be rear subframe bushings.

That is, to my knowledge, normal for LSDs... both my 5 and 7 with LSD had slight play.. but we're talking nanometers.
But that could be the problem, or one of the halfshafts could be bad.
To check the halfshafts, go under the car and move them side to side. They should be tight and no noise.

[browntown]

did u have your driveshaft balanced? hows your guibo?

[Ryan Stewart]

a. u joint play. Mine did that before a driveshaft replacement.

b. I have about cooked my diff and am looking at options. Thinking helical.

[static]

FYI: it was diff bushing bolt that came loose

[DanGillan]

that would do it

[sweetride01]

Yea I have a bad diff bushing. I get the same kinda noises. So a good used diff should probably sort that.

[static]

^^ wait , you don't have to change the whole diff, just the bushing

[sweetride01]

I know. But I think that other parts of the diff are also souring, so from my point of view it may be cheaper and more effective to drop a good used diff in.