M-DCT Semantics and Subtleties

[zohaibkhawaja]

After coming to a complete stop on a relatively level surface and letting off the brake pedal, I notice that the car sometimes lurches back just slightly. It feels as if it js relieving pressure from the drivetrain. What exactly results in this? Is this just the clutch disengaging? Thanks.

[NPuter]

Originally Posted by zohaibkhawaja

After coming to a complete stop on a relatively level surface and letting off the brake pedal, I notice that the car sometimes lurches back just slightly. It feels as if it js relieving pressure from the drivetrain. What exactly results in this? Is this just the clutch disengaging? Thanks.

I don't think it's a "lurch back" that you're felling, but quicker braking when you almost come to a stop.
The "low speed assist" of the DCT (which I HATE), keeps the clutch engaged at low speed so you don't have to stay on the gas pedal to keep the car moving. While this is engaged, any braking is counteracting the clutch engagement wanting to push the car forward. Sometimes, the clutch releases right before you stop, and your brake pressure causes the car to stop quicker because you are no longer fighting the engaged clutch. I think this clutch disengagement is probably the released pressure you are feeling.

[zohaibkhawaja]

Originally Posted by NPuter

I don't think it's a "lurch back" that you're felling, but quicker braking when you almost come to a stop.
The "low speed assist" of the DCT (which I HATE), keeps the clutch engaged at low speed so you don't have to stay on the gas pedal to keep the car moving. While this is engaged, any braking is counteracting the clutch engagement wanting to push the car forward. Sometimes, the clutch releases right before you stop, and your brake pressure causes the car to stop quicker because you are no longer fighting the engaged clutch. I think this clutch disengagement is probably the released pressure you are feeling.

Thank you. Would this clutch disengagement be felt after coming to a complete stop and letting off the brake pedal though?

[SD ///M4]

[QUOTE=NPuter;24647745Also, is it advisable to not use the ebrake when you're on a flat surface (to avoid wearing it out)?[/QUOTE]

Since this thread popped up again, I had to reply to this.

I've used a parking brake for over 50 years and I've never had one wear out on any car that I've ever owned, including the S2000 that I had for 13 years. In fact, I've never even heard of an "ebrake" (parking brake) wearing out. I suppose if you drive your car for many, many years and put many, many miles on it it is possible for the parking brake to wear out, but I've never heard of this.

Bottom line, you should ALWAYS use the parking brake, regardless of whether you're parked on a hill or not, whether the car has a manual transmission, automatic transmission or a DCT. That's why it's it's most properly called a parking brake, because you are supposed to use it when you park, not just when it's used in an "emergency". I doubt anyone here has actually used it only as an emergency brake. Trust me, you won't wear it out.

https://en.wikipedia.org/wiki/Parking_brake

[NPuter]

Originally Posted by SD ///M4

Since this thread popped up again, I had to reply to this.

I've used a parking brake for over 50 years and I've never had one wear out on any car that I've ever owned, including the S2000 that I had for 13 years. In fact, I've never even heard of an "ebrake" (parking brake) wearing out. I suppose if you drive your car for many, many years and put many, many miles on it it is possible for the parking brake to wear out, but I've never heard of this.

Bottom line, you should ALWAYS use the parking brake, regardless of whether you're parked on a hill or not, whether the car has a manual transmission, automatic transmission or a DCT. That's why it's it's most properly called a parking brake, because you are supposed to use it when you park, not just when it's used in an "emergency". I doubt anyone here has actually used it only as an emergency brake. Trust me, you won't wear it out.

https://en.wikipedia.org/wiki/Parking_brake

Ok I'm not an idiot where you have to post the wiki page lol

This is my first car with a manual parking brake, and with anything mechanical, constantly cranking it over and over again when unnecessary cannot be "good" for it. I'm just wondering if the F3x/F8x have had any issues with the brake line stretching/failing/etc. My friend wore his brake line out (granted, he had a kia) only a few years into ownership (car rolled out of his driveway at one point).

I already have to crank the hell out of the brake for it to work on any significant hill, so why would I risk making it any worse by setting it e.g. in my garage where I could even leave the car in neutral with it being virtually impossible for it to roll anywhere? That's all I'm saying.

[NPuter]

Originally Posted by zohaibkhawaja

Thank you. Would this clutch disengagement be felt after coming to a complete stop and letting off the brake pedal though?

I don't think there will ever be a time where the clutch is still engaged to any extent after the car comes to a stop

[dezzracer]

Originally Posted by tisme

I agree a good thread, but I expect that within a day or two driving with DCT will come naturally, and I'm picking mine up in 5 weeks 1 hour and 22 minutes.

Took me a couple weeks to learn how to use DCT correctly in all conditions. In the first couple days I felt like a complete goon. Lol

[dezzracer]

[QUOTE=WVUDrJay;17428346]

Originally Posted by khaye1

you're wife will be fine...just don't let her drive it!

Fixed for you.

Lol. Good advice.

[SenorRoadRage]

Apologies if this has been asked but I skimmed through a few pages and didn’t see it.

I got my first M (2015 M4) a few weeks ago and am wondering at what point do the clutches disengage while coasting? The reason I’m asking is because my car hates the parking garage - especially in the morning before she’s had her coffee and is warmed up. When leaving in the AM I’m going downhill and coasting around the bends. When it’s time to get back on the gas it seems like the clutches engage and she’s lurches around a bit. It happens going around the corners on the way up too, but not as bad.

I think it’s all normal and it’s something to get used to though. D1 helps a little too and I’ve been driving the first 5 miles or so in Sport/D1 until it gets a little warmer then hit S+/D3. Keeping slight pressure on the accelerator around the corner works too but is a bit dangerous...

[2 SLOW]

Originally Posted by SenorRoadRage

Apologies if this has been asked but I skimmed through a few pages and didn’t see it.

I got my first M (2015 M4) a few weeks ago and am wondering at what point do the clutches disengage while coasting? The reason I’m asking is because my car hates the parking garage - especially in the morning before she’s had her coffee and is warmed up. When leaving in the AM I’m going downhill and coasting around the bends. When it’s time to get back on the gas it seems like the clutches engage and she’s lurches around a bit. It happens going around the corners on the way up too, but not as bad.

I think it’s all normal and it’s something to get used to though. D1 helps a little too and I’ve been driving the first 5 miles or so in Sport/D1 until it gets a little warmer then hit S+/D3. Keeping slight pressure on the accelerator around the corner works too but is a bit dangerous...

Don’t change it out of Efficient/D1 until after you leave the garage. I also don’t see the benefit of D3 over D2.

[dallastide]

Originally Posted by SenorRoadRage

Apologies if this has been asked but I skimmed through a few pages and didn’t see it.

I got my first M (2015 M4) a few weeks ago and am wondering at what point do the clutches disengage while coasting? The reason I’m asking is because my car hates the parking garage - especially in the morning before she’s had her coffee and is warmed up. When leaving in the AM I’m going downhill and coasting around the bends. When it’s time to get back on the gas it seems like the clutches engage and she’s lurches around a bit. It happens going around the corners on the way up too, but not as bad.

I think it’s all normal and it’s something to get used to though. D1 helps a little too and I’ve been driving the first 5 miles or so in Sport/D1 until it gets a little warmer then hit S+/D3. Keeping slight pressure on the accelerator around the corner works too but is a bit dangerous...

Just manually shift to 2nd gear when going downhill in a parking garage. Fixes this entirely.

Also, the first few months I had the car I drove in auto mode but over time I've gotten to where I shift myself 100% of the time. It almost entirely eliminates any jerkiness or lurching issues. And is more fun.

[SenorRoadRage]

Originally Posted by dallastide

Just manually shift to 2nd gear when going downhill in a parking garage. Fixes this entirely.

Also, the first few months I had the car I drove in auto mode but over time I've gotten to where I shift myself 100% of the time. It almost entirely eliminates any jerkiness or lurching issues. And is more fun.

Unfortunately, I've been doing this as well... I pull off and immediately hit second gear, but when I'm coasting around the corner and get back on the gas after ~3 seconds of coasting going ~10mph, it gets a little jumpy.

I think it has to do with it being cold, but it also does it a little, although not as bad, when it's warm.

I'm not super worried about it because it drives really nicely all other times. It's just "new car jitters" I guess.

[mdharper007]

Originally Posted by SenorRoadRage

Unfortunately, I've been doing this as well... I pull off and immediately hit second gear, but when I'm coasting around the corner and get back on the gas after ~3 seconds of coasting going ~10mph, it gets a little jumpy.

I think it has to do with it being cold, but it also does it a little, although not as bad, when it's warm.

I'm not super worried about it because it drives really nicely all other times. It's just "new car jitters" I guess.

In the same boat. Owned it for about 4mos and every time I get into it (not the daily driver, have an old e46 325 thats been chauffeuring me around some 210k miles), I'm convinced there's something wrong with the transmission. Essentially the same things discussed so far in this thread. Happy I found this thread as I was about ready to drive this thing back to the dealer and demand a complete checkout.

[dallastide]

Originally Posted by mdharper007

In the same boat. Owned it for about 4mos and every time I get into it (not the daily driver, have an old e46 325 thats been chauffeuring me around some 210k miles), I'm convinced there's something wrong with the transmission. Essentially the same things discussed so far in this thread. Happy I found this thread as I was about ready to drive this thing back to the dealer and demand a complete checkout.

Yea you have to really feather the accelerator at low speeds on these cars or you will get the dreaded bucking bronco. Punching it and letting up in quick succession will trigger this almost every time. No jerkiness if you roll onto the pedal consistently.

But again the biggest improvement in my DCT experience personally was switching from auto to manual shifting full time.

Enjoy the new M car.

[rmanm4]

If you are looking for the best fix on DCT:

Get your firmware updated to latest first. Then set DCT to S2 or D2. Then drive in Sport or Comfort and not Sport+. Then report back.

I've driven some old DCT cars and they were all very jerky and concerning. When I purchased my new 2020 F82 with DCT it had the latest firmware and its night a day difference.

The main difference you will feel is the low end max torque is now higher up on the curve. This alone along with the latest DCT firmware is the main reason why most of the jerkyness is gone. You will still get a bit of jerk if you in Sport+ and in first gear but its not as bad or violent.

Only downside if you have a 2014/2015 with original firmware is that you will have a much more smoother torque curve, so that violent wheel spinning off the start is much more tamed. The car becomes more drivable i feel.

[dallastide]

Originally Posted by rmanm4

If you are looking for the best fix on DCT:

Get your firmware updated to latest first. Then set DCT to S2 or D2. Then drive in Sport or Comfort and not Sport+. Then report back.

Good point. I forgot about updating my DCT firmware which did make a noticeable difference.

[RNJ15]

Can someone briefly explain the drivelogic? What is the purpose of D1, D2, D3 vs S1, S2, S3?

In what driving situations are the most optimal settings for drivelogic?

When I want to go into run from police mode, D3 or S3? and why?