[Smithn05]

Hi Everyone,

So I ended up in a slanging match on another forum the other day over a question regarding DCT transmissions and whether or not it makes any difference or causes undue wear and tear to leave the gearbox in D when waiting at the lights or to put it into N.

My argument was that it didn't make too much difference as both clutches would be open and with the engine at idle, there was minimal torque, revs , rotational forces acting on the clutches and although the input shafts would not be able to 'freewheel' because there were in gear, there was much less in the way of likely wear and tear on the clutches at idle than if driving at speed in top gear with one clutch engaged and the other not.

I was fairly unceremoniously told I didn't know my ar5e from my elbow and I shouldn't claim to know what I was talking about as I clearly had no idea. It went downhill from there as you can imagine!!

So it got me thinking, is there anyone out there with any good training info on the BMW DCT transmission.

I am particularly interested in knowing the logic of what the clutches do when the car is in Neutral (they clearly disengage when the car comes to a stop but to they relax/engage when moved to N?).

If they engage when in neutral (and the hydraulics release) I can possible see my opponents point, however from experimenting on my M6 I can only really hear a slight mechanical 'snick' when I move from N to D and back again or from N to R for that matter, which I believe is just the selector forks moving back and forth to engage the gears.

I'm not planning on revisiting my argument with someone that couldn't explain to me why my thoughts were so abhorrent as it will just stoke fires I cant be bothered with, however I am very intrigued!!

There's diddley squat on the internet about the clutch logic (other than they swap as they change to the next preselected gear) so if anyone has any official BMW info / training etc and can definitively say what happens and when Id love to hear it!!!

[DanG]

Interesting question. I know that I just keep my DCT in gear at a stop light. I also know my BMW will roll if I don't keep my foot on the brake.

[Smithn05]

Originally Posted by DanG

Interesting question. I know that I just keep my DCT in gear at a stop light. I also know my BMW will roll if I don't keep my foot on the brake.

Yep me too, and the handbook advises it too so you can have the handbrake on and move off straight from D.

As said I can’t see any reason why it should be a problem other than maybe the hydraulics needing to work harder to keep both clutches disengaged ( which might heat up oil etc) but my assumptions are the this is the same situation in both D and N.

Im hoping there might be a BMW tech on here that repairs DCTs or has some decent training who can explain

[TheMidnightNarwhal]

Originally Posted by DanG

Interesting question. I know that I just keep my DCT in gear at a stop light. I also know my BMW will roll if I don't keep my foot on the brake.

Oh wow it does that on your M model? I thought all M's with DCT had no creep, I guess it's just the E9X Ms?

For example my 335is has creep even though it's a DCT but you can flash it out with xHP transmission tune.

[rcracin]

Im not sure if my dct has a tune but it rolls as if in neutral when im at a stop even though it’s in gear. Won’t engage and creep until i touch the accelerator to get it engaged again.

In any case, if you tried to search here for worn out dct clutches, I think you’d get very little results. I rarely read anything about worn out dct clutches.

So anyone arguing about undue wear being in D at a stop light is wasting their time. Just hasn’t been an issue.

[Redd]

Your opponent also probably shifts to N when he's coasting downhill to 'save on clutch wear'. Just leave it in D and drive the car.

[tranquility]

I supposed it depends on what car you guys are talking about but that's one of the features MT ppl slag on about the DCT saying it's like an AT and in this respect they're right, you just leave it in D at the lights and there's nothing wrong w that.

[Smithn05]

Originally Posted by rcracin

Im not sure if my dct has a tune but it rolls as if in neutral when im at a stop even though it’s in gear. Won’t engage and creep until i touch the accelerator to get it engaged again.

In any case, if you tried to search here for worn out dct clutches, I think you’d get very little results. I rarely read anything about worn out dct clutches.

So anyone arguing about undue wear being in D at a stop light is wasting their time. Just hasn’t been an issue.

Yep that’s actually a very good point, there not lots of bad reports or threats of class actions etc.