clunking driveline low RPM

[cosmo]

I'm trying to figure out what causes the driveline clunk on my car. It's only happening on low (around 1000) rpm and on very little throttle input. I recorded a little video to show the clunk:

https://youtu.be/SW564IBS9XQ

This is a very mild example, sometimes the clunk gets very bad to a point where the car heavily bounces forward/back. This gets super annoying when sitting in LA traffic on a daily basis.

I just got the car a few months ago and changed:

• Flexjoint
• Center Support Bearing
• CV axles
• Rear shocks + mounts
• Swaybar endlinks
• Swaybar bushings
• Transmission Crossmember and mounts
• Diff mount
• cleaned ICV (car idles fine)

I noticed that there is a good amount of transmission output shaft play (maybe around 10degrees) I'm not sure if this is within spec or not.
I visually inspected the subframe mounts and they seem OK. I can't hear nor feel any clunks when going over bumps, so I assumed it must be driveline related.


Thanks for your input!

[varg]

I've had a similar though a little less intense low speed clunk in my car with all 3 transmissions, 2 driveshafts and 3 differentials I've had. I think it's a combination of the lash in the half shafts, transmission and rear end. FWIW all normal wear parts in my driveline (guibo, clutch, CSB and carrier) and suspension (bushings, shocks and mounts) are a couple of years old max. These old getrags tend to be a little loose, that's why they rattle at idle with the clutch engaged, I'm not sure how much play is "normal" but every one I've touched (6) has had a enough play that you could grab the guibo/output flange and twist it for a nice little clunk when in gear.

[cosmo]

Thanks for your input!
I was afraid of it being the transmission, I checked the driveline for any lash and the only one I found was right at the transmission output shaft (besides CVs which I replaced right after).
I guess I'll have to get a catuned rebuilt transmission? I called aamco and they quoted me ~2k also.

[Ebenezer]

I kind of have the same problem. I think it's the transmission as well. Seems like getrags do have a small amount of play in the gearbox. I ended up changing the clutch a while ago and it seemed to almost completely eliminate the clunking to a certain degree. It just recently came back though, and I know my center support bearing and bushings attached to the driveline are all good (replaced them with brand new ones). I also replaced the guibo, since the old one was pretty much falling apart. It's quite the annoyance, and I really want to fix it. Makes the car sound and feel a lot older than it really is.

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[jawkDNA]

Literally, this just started on my 1987 325e last night...
same exact sound under low speed acceleration.

[Maddog]

Check your engine mounts, too.

[cosmo]

Just a quick update, turns out my brand new (FEQ) CV axles have massive amount of play in the CV joints. Bought another set, same problem
Got some used axles in good condition now, I am positive this will eliminate the clunk

[Ebenezer]

Keep us updated. I want to get rid of The driveline clunk

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[jawkDNA]

Curiously awaiting your results...

[cosmo]

took a little longer as I did the Z3 rack swap (what a difference!!)
I installed the 'new' (used, OEM) axles and it is still clunking. I believe it got a little better, but is definitely still there and noticeable when driving. Not too surprising as the oem axles still have some play in them, no wonder after 30 years. I will get them rebuilt now and will report back asap!

[cosmo]

So I finally got the OEM axles installed, took a little longer since I did the Z3 rack swap too. Unfortunately the clunk is still here, might be a little less but definitely noticeable and annoying as hell. The axles still have a little bit of play, although nowhere near as bad es the FEQ ones. I will get the joints rebuilt to rule them out once and for all.
Are there any specs on how much backlash is normal on the transmission and diff?

[Ebenezer]

Are there any specs on how much backlash is normal on the transmission and diff?

I haven't seen any specs on the internet. I know the transmission itself might have a little play. I can twist my driveshaft side to side when it's in gear, but idk if it's normal or a written tranny


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[mitchlikesbikes]

as stated by someone else, old getrags have some slop that's pretty much unavoidable. that could be the source. the differential should have very little freeplay at all, so if there's much it needs to be rebuilt/reshimmed. as also stated before, what you're feeling could be a combination of the slack in all of these components getting taken at once when you engage the clutch. double check your trans and engine mounts too