M-DCT Semantics and Subtleties

[pikkagtr]

I always drive in s2 and shift by myself, but find it very smooth if I come to a full stop just braking from say <30 mph and letting the DCT shift down to 1st by itself.

[omgwtfbbqm4]

Originally Posted by curvehound

1) Slowing for a stoplight in S or D mode, when the DCT shifts itself from 3rd to 2nd, the shift is very “clunky” (ie the car slows abruptly). Is there any way to make it smoother? Obviously I can shift into neutral when I am coasting to a light, but is there any other way? I have tried riding the brake a little or the throttle - both help somewhat but it does not always avoid the abrupt shift.

The trick is to brake harder and slow down quicker. I find what's happening is that if you brake too softly, it'll shift 3rd->2nd but then disengage 2nd a second later. 2nd gear has a ton of engine braking power. This is what you're feeling. If you brake harder and stop quicker, the car will skip engaging 2nd and just coast from 3rd->disengage instead of 3rd->2nd(for a second)->disengage

[BwoodBMW]

Yeah the DCT actually had a bit of a learning curve. I'm 1500 miles in and still get the buckin bronco every once and a while

[///M-er-gized]

So, in other words, when I get my M3 and pull into the garage the first time, I'm going to slam into the beer fridge.

[TRZ06]

The M DCT works different than a tradition auto, it behaves more like a true manual without the third pedal.

After a stop and you release the brake, the car is basically in "clutch pressed in" mode, its not until you tap on the gas, that it "releases the clutch pedal"

I was in an Adui S4 previous to the M and it was the double clutch, but acted more like an auto as it would creep in gear as soon as you let off the brake.

The M is only my second car with a dual clutch, so I don't know how Porsches, Ferrari's work, but I like the M DCT as it acts more like a true manual.

My issue isn't with the clutch engaging, but sometimes when accelerating in 1st the car will buck and jerk. I don't think that is related to the clutch, but maybe the driveline, I am not sure.

[curvehound]

Originally Posted by mkoesel

With regard to S mode in particular, don't let the transmission downshift itself. It is only downshifting for you at the very last opportunity to avoid a stall. Think of this situation as similar to driving a car with a manual transmission when the you forget to clutch in or downshift while coming to a stop and the car begins to shudder as the driveshaft's RPM threatens to pull the engine below idle RPM. It may not be quite that dire, but you are nevertheless calling on the TCU to rescue you in a similar way. Instead, you should be properly downshifting as RPM falls. I generally avoid any RPM below 2K, except in first gear of course. If you use S1 you can also choose to stay in second gear (car will not try to go to first gear).

Now I don't use D mode, but in that case if you choose D3 or, I believe D2, the car should be aggressive enough with rev matching to keep RPM from falling too low.

Also, if you are coasting to a stop rather than braking, this typically causes the car to hold gears longer as well. So, for example, if you combine engine braking with not manually downshifting with the least aggressive Drivelogic settings, you are achieving the trifecta of poor transmission dynamics.

By the way, you should never need to use neutral in normal, day-to-day driving. Disconnecting the engine from the wheels is generally not good practice regardless of which type of transmission we are talking about. You want to be able to use the throttle effectively to change speed at a moments notice. And, especially when cornering, you want to be able to affect the cars tragectory with throttle input.

Thanks to all for the helpful posts - sorry for the delayed reply back.
Based on some of the posts I think I was not very clear. The only time I have had trouble with the DCT shifting “unsmoothly” is when I am coasting to a stop. Under most normal driving conditions, I think this DCT is significantly more smooth and predictable than the previous generation.

Mkosel, I think your suggestions to shift down manually when slowing to a stop is a good one. I will try that and also take yours and others advice to brake harder.

I only was shifting to N when I was coming to a stoplight. I agree that it is not wise to go to N when driving.

Thanks again
Ian

[curvehound]

Originally Posted by tke743

1)

2) Lightly tap the throttle, LIGHTLY. It goes into creap mode. The catch is that when cold creap mode is lunge mode and scary! Wait for the cold start to drop below 1000 rpms.

Us Ian's got to stick together.

Thanks Ian

Yes, I think the problem has been exaggerated by the cold weather, making the idle faster when I am pulling out of the garage in the morning. I will try to be more patient.

Ian

[curvehound]

Originally Posted by ///M-er-gized

So, in other words, when I get my M3 and pull into the garage the first time, I'm going to slam into the beer fridge.

Yes you will. It is inevitable. Try to remember to empty the fridge before your first drive.

Enjoy the car

Ian

[m4pewpew]

Originally Posted by mkoesel

With regard to S mode in particular, don't let the transmission downshift itself. It is only downshifting for you at the very last opportunity to avoid a stall. Think of this situation as similar to driving a car with a manual transmission when the you forget to clutch in or downshift while coming to a stop and the car begins to shudder as the driveshaft's RPM threatens to pull the engine below idle RPM. It may not be quite that dire, but you are nevertheless calling on the TCU to rescue you in a similar way. Instead, you should be properly downshifting as RPM falls. I generally avoid any RPM below 2K, except in first gear of course. If you use S1 you can also choose to stay in second gear (car will not try to go to first gear).

Now I don't use D mode, but in that case if you choose D3 or, I believe D2, the car should be aggressive enough with rev matching to keep RPM from falling too low.

Also, if you are coasting to a stop rather than braking, this typically causes the car to hold gears longer as well. So, for example, if you combine engine braking with not manually downshifting with the least aggressive Drivelogic settings, you are achieving the trifecta of poor transmission dynamics.

By the way, you should never need to use neutral in normal, day-to-day driving. Disconnecting the engine from the wheels is generally not good practice regardless of which type of transmission we are talking about. You want to be able to use the throttle effectively to change speed at a moments notice. And, especially when cornering, you want to be able to affect the cars tragectory with throttle input.

So with DCT, I've developed this habit of letting the car downshift for me from 2nd to 1st to get the smoothest shift. Is this bad for the car?

[M4Now!]

^ No. In fact it's probably better, as the tranny can choose the optimal conditions at which to shift.

Cheers

[tke743]

Originally Posted by ///M-er-gized

So, in other words, when I get my M3 and pull into the garage the first time, I'm going to slam into the beer fridge.

Actually no, if you are not in cold startup mode you should be fine. The trick is learning how to engage creep mode. You need to very very lightly tap the throttle, not enough to even blip the throttle. It will engage and creep forward. Think of it as a centrifugal clutch. You can also modulate it with your left foot on the brake.

All of the above, is null and void if you're in cold startup mode. Cold startup mode + creep mode = lunge forward at the speed of light mode. That is very scary.

[mkoesel]

Originally Posted by m4pewpew

So with DCT, I've developed this habit of letting the car downshift for me from 2nd to 1st to get the smoothest shift. Is this bad for the car?

I presume from context you are speaking specifically with respect to S mode. In D mode you obviously don't need to worry about shifting at all.

The answer is no. The transmission's software is designed to protect the car from stalling. But even if the car would actually allow a stall, it wouldn't particularly be bad for the car (though I suppose it could cause unnecessary clutch slippage). Now, in 2nd gear the car will creep around at idle RPM anyway, so there isn't the same necessity to select 1st gear. The anti-stall mechanism is really only a factor in higher gears, such as 3rd to 2nd as the OP mentioned.

[paliknight]

Originally Posted by mkoesel

I presume from context you are speaking specifically with respect to S mode. In D mode you obviously don't need to worry about shifting at all.

The answer is no. The transmission's software is designed to protect the car from stalling. But even if the car would actually allow a stall, it wouldn't particularly be bad for the car (though I suppose it could cause unnecessary clutch slippage). Now, in 2nd gear the car will creep around at idle RPM anyway, so there isn't the same necessity to select 1st gear. The anti-stall mechanism is really only a factor in higher gears, such as 3rd to 2nd as the OP mentioned.

Can a DCT ever stall?

[GrussGott]

Originally Posted by curvehound

Thanks to all for the helpful posts - sorry for the delayed reply back.
Based on some of the posts I think I was not very clear. The only time I have had trouble with the DCT shifting “unsmoothly” is when I am coasting to a stop. Under most normal driving conditions, I think this DCT is significantly more smooth and predictable than the previous generation.

Mkosel, I think your suggestions to shift down manually when slowing to a stop is a good one. I will try that and also take yours and others advice to brake harder.

I only was shifting to N when I was coming to a stoplight. I agree that it is not wise to go to N when driving.

Thanks again
Ian

(1.) I always drive in S (manually) but I never downshift unless I want to engine brake, like on the freeway, or punch it ... like on the freeway or other times

If I'm coming up to a stoplight I just apply the brake, don't touch the gears, and there's zero downshift sensation in any way ... the numbers just change from 5 down to 1 or whatever. Nobody would ever know the car was downshifting.

I think if you're driving in "3" in either mode the car is going to shift hard so if you want smooth you should be in 1. That said, again, no matter what S settings I have, I just use the brake and get no down shift jerkiness in any way.


(2.) For reverse, and starting out, it helped me to realize that the accelerator pedal is a combined clutch and accelerator. So the same car behavior in an MT happens when pushing the accelerator - you're letting out the clutch until the car "catches" and then it's ready to go so no different than a manual in reverse. I've just learned that the first few centimeters of travel are the clutch and the rest is the accelerator.

[pertierr]

Originally Posted by curvehound

Am I the only one who is having these issues?
Ian

No, you're not imagining it. This is my first DCT ever and like you I was surprised, I expected it to behave like an automatic except shift faster, but it really is a different beast.

Part of me thinks this is just the price to pay for such lightning quick shifts, and it is a low price.

However, my other side thinks that the software could be refined quite a bit.

Does anyone know if there have been any firmware updates for the DCT on this car?

[mkoesel]

Originally Posted by paliknight

Can a DCT ever stall?

I wouldn't say never, but a properly functioning one shouldn't. I have had my car sputter and lurch on occasion when I've forgotten to downshift (I use S3 mode exclusively). It isn't something to dwell on and be concerned about, but it is still important to know how the transmission operates and how to get the best experience from it.

[m4pewpew]

Originally Posted by mkoesel

I presume from context you are speaking specifically with respect to S mode. In D mode you obviously don't need to worry about shifting at all.

The answer is no. The transmission's software is designed to protect the car from stalling. But even if the car would actually allow a stall, it wouldn't particularly be bad for the car (though I suppose it could cause unnecessary clutch slippage). Now, in 2nd gear the car will creep around at idle RPM anyway, so there isn't the same necessity to select 1st gear. The anti-stall mechanism is really only a factor in higher gears, such as 3rd to 2nd as the OP mentioned.

Thanks!!

[aboulfad]

I let the car downshift in S mode as I found sometimes when I am in 3rd and I downshift, only to find that I initiated the downshift at the same time that the car was doing a 3 to 2 and I end up in 1st at undesirable speeds. I guess my timing is bad so I initiate upshifts and let the car downshift in manual mode!

[Ghosn]

I don't think this valet received the "How to drive a DCT" memo

[Arcades]

Huh...

I didn't realize S downshifted for you... Maybe I can try playing a bit with S now...

Learning something new each day~

[CanAutM3]

Originally Posted by mkoesel

I generally avoid any RPM below 2K, except in first gear of course.

That's interesting.

When puttering around on the DD, I rarely have the revs ABOVE 2K, except in 1st gear.

[m630]

Then there is no reason to have an M! For DD driving on local roads, u never need to get out of 3rd-4th max. Drive the beast like its made to