M3 DCT Issues - 1200 miles in 5 days

[alvinjamur]

I've put around 1200 miles after getting my M3 DCT last week - drove
it from nyc to montrea and back, and then some upstate etc. Taking
it into service tomorrow. Like many others on this forum, here is an
issue I've had :

am at a traffic light, on an incline. car is in 1st gear, my foot on the
brakes. light goes green. foot releases brakes, i hit the gas pedal.
the engine revs but NOTHING happens...the car starts rolling backward.
i hit the brakes again. try the same routine again and the car rolls
backward. i then turn off the car, start up again, and then hit the
gas pedal...the car jerks and moves forward.

For sure, there are some software related issues. i hope that somebody
at BMW North America is reading this forum to get user feedback on the
new DCT boxes.

- aLV

[synclastica_86]

Don't be so sure, it might not be a software problem. It sounds like a clutch problem to me. When your car rolled back, was the clutch engaged at all or was it just slipping? If it's slipping that means that it might be over heating. How did you put all the 1200 miles? Did you stay within the reccomended rev range and speed? You didn't use launch control right? If you do as told there shouldn't be any damage, don't worry.

I've had the same experience before. It usually happens after a few hard launches and burnouts, especially on road surfaces that the tyres can hook easily. The fluid might get hot enough for it to boil and the bubbles formed will cause the system to lose pressure. This prevents the clutch from engaging. Give it a while and let the car cool then it should be fine.

Try it with a cold car, perhaps after a lengthy cruise without any shifts. Your problem should not happen. If it persists, try starting in second. The other clutch is used for even gears. This might help isolate the problem. It is the first clutch that take most of the punishment since it is always used to pull a standing car. Starting the car in second some of the time will help keep wear balanced.