bmwe21.net forums

As I don't see people replying on the same post on my build thread, I thought of asking here
it's about the driveline/transmission noises I hear after the various changes n the car.
I guess some part of these might be from the poly bushes-already posted elsewhere.
However, I noticed that some kind of noise that seriously combines to the total noise result of the car (engine etc) is coming from somewhere after gearbox, because, when I change +/- gear, its frequency remains unchanged, it just stops for one second(or so: during shifting time when the gas pedal is not pressed) and then it continues exactly the same, even though engine rpm may have fallen(or risen, depending on gear change)
Now, trying to describe that noise, it is a constant noise a bit like when a car moves in reverse gear. It is not that bad, but it can be heard-especially in 4th and 5th gears, but also with the others (engine noise covers it more when km/h are low and rpm are high)
I am pretty sure its frequency depends on km/h and not on engine rpm.
So I guess it's coming from the diff but I am not so sure whether it is a bad noise (means that diff has an issue) or it is normal for an lsd for instance, as I haven't had an lsd before.
So I wonder whether in general lsd diffs are from construction a bit noisier than open ones
Or should it be quiet?

Yes they are .. not alot but you defenately hear them a little more .. but as I read your description the release clutch bearing might also be the problem .. this gives exactly the noise you are referring to

What is the release clutch bearing?
You mean it's outside the diff housing?

ok, now I looked it up
But, does this bearing move while the car is speeding up?
Or its use is only when changing gears?

The clutch release bearing is in the front of the gearbox .. if the noise is gone when you press the clutch then thats your problem .. it moves also when the car speeds up

Do you have the noise when driving or also when the car is standing still with engine running

Could also be the drive shaft bearing ..

No, only when driving

However, the noise frequency as I wrote doesn't change with rpm but with car speed
So as this bearing is before the final drive shaft, shouldn't its frequency be increasing with engine speed (= rpm) ?

Sounds like a diff or wheel bearing noise to me.

Ok, so in all cases guesses are towards "bearings" and not something more complicated or serious ?

Looks like some kind of bearing yes ... you can check for wheel bearing issues easy .. when the noise gets louder turning right or left its sure to be a wheel bearing .. if the noise is always the same then probably diff or drive shaft bearing

Ok, I 'll check this and come back to inform here.
In any way thanks guys

sorry cant really compare to a non lsd driven e21 s I always had my e21 running on an lsd, but there is a small whine at the rear of my car also, always guessed that the prop shaft bearing or the diff bearings were slightly worn, but upon further research seems that this could be normal for lsd diffs so maybe nothing to worry about?

Oh, here we are, this is the thread I was looking for, nice idea to continue here...
As I keep on searching whether the noise produced from my diff is normal or an indication of wear, and as in another thread we started from talking about possible oil additives in order to decrease/stop the noise, and ended in bushes replacement, I was wondering: What happens to a car that has SOME of the old rubber bushes replaced by poly ones and the rest NOT?(I mean, the rest is kept as was, the old rubber ones, not new rubber)
Could it be that the old ones start getting a lot more stress BECAUSE of the new stiffer ones, or is it irrelevant? - as I saw from my order in Eurometric, that I have not replaced the diff bushes by poly ones. (So I was wondering whether I should replace these as well, and from what material?)

4.1 open diff - no sound at all
3.45 LSD - light howling sound on high speed
4.1 open diff case with swaped LSD unit in it - increased howling sound at every speed
3.91 LSD - ligt/medium howling sound at every speed (like noisy winter tyres)

If by "howling" sound you mean the sound reminding-not precisely but close enough- of a car on reverse gear (come on, this is very characteristic on most cars isn't it?), then this is the sound I hear.
My diff is a 3.64 lsd, (11-40 teeth) which I ordered from Nas, who claimed it was an E21 lsd with E36 (168mm) ring and pinion swap. This sound is heard almost at all speeds, but only with gear in. Not heard when clutch is pressed or with neutral, only heard with gear in, when gas pedal is pressed

Found this article:

http://www.superstreetonline.com/how-to ... nsmission/

Could it be my (dog leg) gearbox and not diff, finally? And this howling or whine sound be normal?