clunk/thump when pushing clutch at low speeds

[static]

Hi crew

For some time i thought that this was due to me having ltw flywheel, but now a buddy of mine chimed in mentioning he's got exactly the same problem on his s52 swapped e30, and connecting link is that it was the same mechanic who did both of our conversions. (he is a great bmw mechanic though and been around bimmers forever)
He has a normal stock heavy flywheel and we both have ZF tranny.

Here is how to reproduce the problem: when the car is warmed up, go in 1st gear, give a bit of gas, then lift for like a half second, then push clutch all the way in - the result is a series of dull clunks/thumps with reducing loudness. If I skip the half-second accel lift before pushing clutch in, the clunk is not there (so i guess it is directly influenced by the load on the driveline)

So my question is: what could that be possibly caused by?


Alex

[PiercedE30]

maybe CSB....could be a soft rubber in the csb itself that gets warmed up and loosens up as the exhaust piping warms, this would allow it to flex some and giving you some play in the driveline.

[Brew]

Possibly subframe bushings...

[Mr.SWISS]

Possibly subframe bushings...

So is it normal for my RSFB to come out about 1/2" when I lift the car? I am trying to track down my thump and have replaced the RSM'S, Axles are brand new, drive shaft has a fresh CSB and guibo done at time of swap, and the diff was swapped for a LSD out of an auto 535is. I didn't notice it until I got the new diff in and there is 0 play in the shaft and minimal from the ds input to the axle.

[static]

it's not SFB, RTABs, not rear tower mounts and not driveshaft bearing - all these had been replaced by both of us during the swap

[davem]

I have this same issues... pressing the clutch pedal when I'm driving at low speeds and low rpms (parking lot situations for example) results in a loud CLUNK. I did some experimenting today and noticed that if I accelerate from stop with a lot of throttle/revs and then press the clutch it doesn't clunk, if I wait until the revs go down to about 1000k rpms and then press the clutch, CLUNK!

Info about the car - the maintenance mentioned is all recent and didn't change the symptoms (although this never happened when the car was an automatic).
-auto to five speed swap
-no clutch return spring on the clutch pedal
-new slave & master cylinder
-clutch, t/o bearing, pilot bearing replaced
-shifter bushings replaced
-new guibo
-remanufactured drives shaft and new CSB
-subframe, rtab, differential bushing replaced
-strut and shock mounts replaced
-shocks replaced
-one of the cv axles was replaced for one in slightly better condition
-transmission mounts

[davem]

Shit, didn't realize that this post was originally made in the 24v forum. Can a mod move this, or perhaps make it into a new thread? Sorry!

[VinniE30]

I had the same exact symptoms and it ended up being really badly worn subframe bushings.

[davem]

I had the same exact symptoms and it ended up being really badly worn subframe bushings.

Mine are brand new.

[russhixmo]

Mine does it when u put it in gear and take it out and let the clutch up too fast, i dnt think it's anything to worry about though

[Wanganstyle]

If you have a lot of backlash in your ring and pinion setup (in the diff) this can happen at low speeds when getting on/off the throttle.

[davem]

If you have a lot of backlash in your ring and pinion setup (in the diff) this can happen at low speeds when getting on/off the throttle.

I don't remember this when the car was an automatic though... is it possible that it is flywheel/clutch related?

[Balleristic31]

My diff clunks like no other. And since u said it didn't do it until u swapped diffs... I'd check there.

[Wanganstyle]

having a clutch and flywheel is more jolting than the gentle lock up of a OEM torque convertor.

easy way to see:

put rear of car in air. turn either driveshaft or one of the wheels and see how much play/slop there is before the ring and pinion engage. Open diffs will have tires spin opposite and show the play of the gears directly, LSD cars will show gear play and LSD unit lock up play if you give it some rotational speed (and the tires mass)

E28/e30 era diffs are very old; although the ring and pinion units are same as any 188mm and can stand alot of power, the items wear over time and should be re-set to prevent excessive play. You can reference the e30 OEM BMW TIS on this procedure :)

[davem]

having a clutch and flywheel is more jolting than the gentle lock up of a OEM torque convertor.

easy way to see:

put rear of car in air. turn either driveshaft or one of the wheels and see how much play/slop there is before the ring and pinion engage. Open diffs will have tires spin opposite and show the play of the gears directly, LSD cars will show gear play and LSD unit lock up play if you give it some rotational speed (and the tires mass)

E28/e30 era diffs are very old; although the ring and pinion units are same as any 188mm and can stand alot of power, the items wear over time and should be re-set to prevent excessive play. You can reference the e30 OEM BMW TIS on this procedure :)

hmmm that's odd, my car only has about 190k kms (118k kms). What is this procedure called and what is the TIS? The Bentley manual doesn't appear to touch on this subject.