Evening all,

I’ve got a 3.6tdv8 with the zf6 speed gearbox. Recently I have a strange fault where the car will just slip when in gear. I can rev the car to 3000rpm with no movement when in drive, sport, manual or reverse.
This is followed by a whirring noise from the bell housing area that disappears in neutral, when stationary and putting it into there is a grinding noise, im guessing the park mechanism is grinding as the gearbox is still spinning slightly when stationary.

The only way to sort this is to constantly changed from drive to reverse and eventually it will engage. Gearbox oil level is correct with nothing obvious. To make matters stranger I can put my foot hard down and most of the time it will not slip.

Anyone got any ideas?

No fault codes present either.

Have you checked the pivot where the selector cable attaches to the lever on the side of the transmission is free to rotate?

Yes this appears to work correctly. I believe it selects gear fine, when it loses drive and starts making the whirring noise it still displays D in the instrument cluster and if revved to 3500-4000rpm it very slowly starts moving (the speed it moves is about half the speed of first gear low range at idle)

Draw off a bit of transmission oil and check for metal flecks, it could be the torque converter on it's way out or something more serious.

Funny enough I did that this morning. Couldn’t see any metal but the oil is pitch black and the car has only done 115,000miles. Changed the oil in zf6 gearboxes previously in BMWs I’ve owned and never seen the oil this dark.

When you say the oil level is correct, how did you check it? TBH, unless there is evidence of a leak (or coolant in the oil) then the level should be OK - 115k is way past the accepted life of the oil.

The fault could also be downstream of the transmission e.g. output shaft spline, or maybe the transfer box or a driveshaft joint popped out?

Phil

Oil level was checked with the oil between 35 and 40 degrees. I had some zf lifeguard 6 lying around from a previous car. So drained a litre and then when at the correct temperature it took nearly 2 litres, unfortunately this made no difference.

Was that with the engine running?
Good point about the rest of the drivetrain, it's possible for the transfer box input shaft splines to wear, although this would be a noisy and permanent loss of drive

Yes engine running.

I can’t see it being spline wear as it doesn’t regain drive. When there is a noise it comes from the bell housing area.

So back to the TC / flexplate then. I have seen a flexplate cracked all the way around, that was caused by the transmission being refitted without one of the alignment dowels being in place causing the TC alignment to be off-centre enough to gradually rip itself away from the crank fixings....