Transmission clunk - Could it be transmission/diff oil?

G

GaryCZ4

Member
Hi all - I have a 6 speed 3.0Si E86 6 speed Manual, and there is a 'clunk' when i accelerate/take foot off gas in the lower gears - It is not bad, but not ideal. My initial thoughts were center bearing or flexi donut on prop which is not a major job, but because the bolts on the exhaust downpipe are rusted out, is a bit of a pain to get at; I've been quoted around £200 to have them drilled out and replaced.
This week has been very cold, and I have notice that the clunk is non existent until I have driven a few miles. I am not sure if this is coincidental, but not sure why it should not be there in the cold which has made me consider if it's oil related. The cold oil being thicker and reducing any noise.

Any suggestioons would be gratefully accepted, also, does the diff have a drain plug or will I need to pump out the old oil?

Thanks in advance!
 
I can imagine thick oil hiding play in the gears/synchros but at that point it's a box problem. You could drain it and see if there's more than the usual silver slurry on the magnet.

Rear diffs: Up to late 2006 they've got a drain plug and then it disappears.
 
Many thanks - Car is Oct 2007 so probably no drain plug - Real OEM show schematic diagram and can't see from that. I'm off the opinion that it is more likely prop related but want to rule everything else out before I start disassembling exhaust etc to access it.
 
Just a thought... Could be cold rubber is more solid than soft rubber, so as it warms up, the rubber gets softer and lets it clunk?

That said, I doubt the temperatures involved would be that extreme, so this is a bit tenuous, but maybe the guibo is close enough to the gearbox there is enough heat transfer?

I think you can get to the propshaft without removing the exhaust (just reaching past some heat shields) to check for play in the prop?
 
Yes, cold rubber has crossed my mind. My son who is a BMW technician believes it’s more likely prop related, but just odd that it disappears in the cold (-3c).
 
99% of the chance is rear diff bushing

I got the same symptom and found that my big rear diff bushing is cracked, it is a common issue in E46 and E85 rear axle as they share the same design

Clunk is gone after I replace it
 
yes 100% sounds like the prop Guibo - its like a rubber donut that takes the harshness out. Mine sounded the same and was easy enough to replace and all good now.
 
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