DIY: Driveline clunk at clutch engagement - BMW M5 Forum and M6 Forums
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post #1 of 4 Old 14th December 2018, 05:20 PM Thread Starter
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Driveline clunk at clutch engagement

Ok, so yes I've searched, but most threads on the topic don't seem to come to a final conclusion. Plus I know some of the usual culprits but have so far more or less ruled them out. My suspicion is that this is a fairly common issue in our cars with 2 or 3 different route causes, but throwing parts at things has so far prevented anyone from really narrowing things down yet. Maybe this time we'll finally change that. Please feel free to chime in with thoughts, and I'll update as I continue to work through things. Now, to business:

E30 MY2000 540i/6

Hear/feel a bit of a 'clunk' from the driveline right at the point of clutch engagement. Also a smaller bit when quickly transitioning from throttle on/off. More pronounced when cold than when hot. Clearly this is some slop/lash somewhere in the drivetrain, but the trick is to narrow it down to which part(s) and why it has worsened over time?

Possible causes:
Normal amount of lash present, nothing to worry about, live with it. <- I don't believe this is the case. Yes there must be some lash in the system clearly, but I've driven other similar cars where it's either more or less noticeable than my car. Plus I believe that is has worsened somewhat over time (~20,000 miles of my ownership).

Increased gear lash due to wear in transmission and/or differential, rebuild/replace is only path to improvement. <- Possible, but I think unlikely for several reasons: A.) Heat treated gear metal wears very slowly, especially when properly lubricated. Also, I well above average when it comes to maintenance and driving. I change the transmission and differential fluid on my vehicles regularly (2-3 years or maybe 20,000 miles) with high quality stuff, and I have properly heel/toe rev-matched every downshift I've ever made in my entire life. And again, I've driven other cars with higher mileage that I know are not pampered as much as mine that are 'better.' Maybe popping off the diff cover at the next fluid change and peeking at the gears is still worthwhile, but like I said I consider this pretty unlikely.

Driveshaft components, e.g. guibo, center bearing, and rear CV joint. <- Visual inspection and very, very little play in the driveshaft in all gears with parking brake on make me think these parts are probably all fine. Or is checking them stationary with just a hand wrench amount of torque not adequate for assessment?

Front differential bushing. <- Visually looks OK, but how hard should one pry on the thing with a bar to look for movement? How touch is it to replace? Assume removing the diff is necessary, but what tool(s) are then needed to get the sucker out and a new one in there? Worth attempting? At least the part is cheap. . .

Axle shafts/wheel bearings. <- When checking for play with the parking brake off, the greatest amount of slop seems to be in the differential between the two output flanges rather than from the flanges to the wheels. I get maybe 2 degrees of slop between the two flanges, and I'd say less than 1/2 degree from the input flange to the output flanges, and essentially nothing from the output flanges to the wheels. If anything, I guess this points to the diff internals more than anything.

Clutch delay valve. <- A pox on the cursed BMW engineer who thought THAT was a good idea, and an even more nefarious fate to whoever his boss was that signed off on it, but it was removed from my car on day 1 of my ownership. And don't try to convince me that removing this expedited any wear, see above on driving style, moving on.

Dual mass flywheel/clutch springs. <- Now we have an interesting one, as I don't really know how the hell this dual mass system is supposed to work, the potential failure modes of the system, and the associated consequences. Obviously I'm not keen to just drop the transmission for the hell of it, so if anyone can enlighten me with some more details here, I'd very much appreciate it!

Thanks, feel free to share thoughts, and stay tuned if I can find out any more!
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post #2 of 4 Old 3rd January 2019, 03:07 PM
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You might also check out the transmission mounts. They are relatively cheap and easy.

Have you tried seeing how the clunk behaves if you stop and are going up an incline? I know that may be a bit more difficult, but could give an indication as to whether or not it is a component in the driveline which is preloaded (from the weight of the car on the incline) or not.
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post #3 of 4 Old 4th January 2019, 01:49 PM Thread Starter
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I recently replace the transmission mounts, so those are on the unlikely list, but I'll double check then next time I'm up under there. Good idea about starting on an incline though, I'll definitely try that out!
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