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Q: Rear differential clunking noise on 2007 BMW M6

I have a distinct clunking noise from the rear differential especially in the drive mode of the smg. After coming to a complete stop, the transmission is slow to engage first gear upon acceleration and again experience a loud clunk and slam into gear.

I have had the BMW rear end bulletin lubrication fluid replacement performed but no difference.
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This clunk definitely needs to be investigated if it is the drive shaft and it fails it could cause you to loose control of the vehicle, if it something failing in the differential and it breaks it could cause the rear end to lock and cause a skid.
Check the hydraulic unit for leaks. Make sure the hydr.fluid level is correct. Use only Penthosyn CHF 11S fluid. If the level is low it may also need to be bled.
Did the shop run a computer diagnostic on the SMG transmission?
How many miles are in the car? I have seen clutch assemblies failing at fairly low miles.
It's a complex system, don't let incompetent mechanics touch the SMG, only BMW specialty shop or the dealer.

I can only assume that the three BMW shops I have taken the vehicle to for repair have performed the diagnostic. The vehicle now has 34,000 and the clutch is starting to chatter when heated especially when the car starts out in second gear from a dead stop.
The drive train should be covered under a 4 years / 50K miles warranty. I hope you are not over on the 4 years yet.
The SMG is kind of equals to a high performance, racing transmission therefor the lifetime of the clutch and the DM flywheel is a lot shorter than a regular manual transmission's, mostly about one third.
Did any of the shops give you any diagnostic trouble codes? If there was no DTC the problem is mechanical and does not indicate SMG control failure - a good sign.
I guess the SIB33 04 08 bulletin was performed and they lubricated the input flange, which is a common source of the clunk from the differential area.
Did you try the reset procedure? You need to drive a bit above 40 mph in neutral and push down the paddles for about 4 second. This way the SMG will adjust to the worn clutch plates.
The usual lifetime of the clutch is about 40K miles, it will worn down sooner if it used in the "sport" mode - like S6- often. In case of clutch replacement ask the shop to throughly inspect the dual mass flywheel too.
These cars will give you a lot's of driving pleasure, but unfortunately they also come with a pretty high maintenance cost.
I hope you can get your problem resolved soon.


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