Smooth braking in DCT

[cw128]

I'm pretty sure this is normal but as this is the first automatic car I've ever owned I just thought I'd check if everyone else experiences this and also see how other people deal with it. I think it is a combination of an automatic gearbox and more engine braking than I'm used to, but I'll explain.

Lets say I'm doing 60 mph in 4th gear and want to slow down quite quickly to 20 mph for a tight bend and go into 2nd gear. I'm in manual gear change mode rather than automatic so I'm changing down through the gears with the paddles at the same that I'm braking. What I've found extremely noticeable is that when I tap the paddle to change down a gear there is suddenly a sort of "free wheeling" effect and then half a second later the car slows down a lot more than it had been before I changed down a gear (engine braking presumably?). So I find every time I change down a gear whilst braking I have to change how much I'm braking 3 times to achieve a smooth slowing down. e.g: 1. Start braking, 2. changed down a gear so get the free wheeling effect and therefore need to brake harder to compensate, 3. half a second later have to brake less again because of the engine braking kicking in as the gear is engaged.

It doesn't sound bad when written down but I'm finding it pretty hard to get it smooth every time, especially when changing down from say 3rd to 2nd, or 2nd to 1st. If I don't lift off the brake a little after changing down then there's a sudden lurch forward as the engine braking kicks in. It probably wouldn't be that hard to get used to if all I drove was the M3 but I have a manual transmission car that I drive most days as well.

Presumably the free wheeling effect is coming from the clutch being engaged just like it would be in a manual car when you want to change a gear (although I was under the impression a dual clutch system wouldn't really need to do that, but that's probably just me not understanding how it works). Maybe in a manual car I would subconsciously lift off the brake a little as I press the clutch in, but because the car is doing it for you in an automatic then its harder to synchronise your brake pedal pressure with it.

As for the engine braking being a lot harsher than I'm used to - is that just because it is a V8 rather than a 4 cylinder engine like every other car I've driven?

But yeah... does this sound normal to you guys and if so, have I got roughly the correct understanding of why it does this? I've only had the car just over a week so there's still plenty of time to get used to it - I'm just curious if anyone else found this a bit annoying at first but got used to it after a while?

[e46m3to135i]

First and foremost mechanically speaking, the DCT is NOT an automatic transmission. What your describing is how the DCT engages and disengages the clutches. From what you have described, it sounds normal to how the DCT functions during those conditions

I noticed this same behavior when I first purchased my car and thought it was kind of annoying. I did find that the more I drove the car, the more I realized I was driving it wrong. The DCT settings have a HUGE part in my opinion on how the DCT operates. I prefer S4 in manual mode and D4 for daily spirited driving. S5 or S6 during aggressive driving. I have found any setting below S/D4 tends to make the DCT a bit more jerkier for daily driving.

The DCT M3 "likes" to be aggressively driven and shifted. I have found that if you can avoid blipping down shifts in a lower RPM's, it actually drives smoother in retrospect to clutch engagement/disengagement when coming to a stop.

A huge improvement one can do in reference to all of this is the GTS DCT flash. I honestly makes the DCT a blast to drive.

It greatly improves the overall function and drivability of the DCT.

-Nick

[to///m]

Originally Posted by e46m3to135i

First and foremost mechanically speaking, the DCT is NOT an automatic transmission. What your describing is how the DCT engages and disengages the clutches. From what you have described, it sounds normal to how the DCT functions during those conditions

I noticed this same behavior when I first purchased my car and thought it was kind of annoying. I did find that the more I drove the car, the more I realized I was driving it wrong. The DCT settings have a HUGE part in my opinion on how the DCT operates. I prefer S4 in manual mode and D4 for daily spirited driving. S5 or S6 during aggressive driving. I have found any setting below S/D4 tends to make the DCT a bit more jerkier for daily driving.

The DCT M3 "likes" to be aggressively driven and shifted. I have found that if you can avoid blipping down shifts in a lower RPM's, it actually drives smoother in retrospect to clutch engagement/disengagement when coming to a stop.

A huge improvement one can do in reference to all of this is the GTS DCT flash. I honestly makes the DCT a blast to drive.

It greatly improves the overall function and drivability of the DCT.

-Nick

this response nails it

[cw128]

Thanks, good to know I'm not the only one that found it annoying at first then and that its perfectly normal. You mention that you were "driving it wrong" but how do you drive it right to avoid having to change how hard you're braking 3 times every time you change down a gear whilst braking? Regardless of which D or S mode I have it in I seem to get the same effect.

What does the GTS flash do then?

[socalm3lover]

Originally Posted by cw128

Thanks, good to know I'm not the only one that found it annoying at first then and that its perfectly normal. You mention that you were "driving it wrong" but how do you drive it right to avoid having to change how hard you're braking 3 times every time you change down a gear whilst braking? Regardless of which D or S mode I have it in I seem to get the same effect.

What does the GTS flash do then?

I have never noticed this. I suspect it has a lot to do with your DCT mode, I am always either in S5 or D5.

I would also like to know what the GTS flash does?

John

[M4Now!]

Originally Posted by e46m3to135i

First and foremost mechanically speaking, the DCT is NOT an automatic transmission. What your describing is how the DCT engages and disengages the clutches. From what you have described, it sounds normal to how the DCT functions during those conditions

-Nick

Not to rehash this argument (and I drive a DCT). But it IS an automatic transmission, it just uses clutches vs. a torque converter, and has a manual mode. If you set it to D, it WILL shift automatically.

Anyway, OP - sounds normal. The downshifts will happen more aggressively depending on settings; and now that you mention it, think I'm now in the habit of downshifting at higher revs, then getting seriously on the brakes after the downshift occurs. That way you have full engine braking, together with brakes.

Cheers

[SenorFunkyPants]

Hmm I've never noticed this...there should not be any "freewheeling" in any gearchange...you may have an old software version, worth checking out, your dealer can tell you what version you are on by using the key reader.
In your scenario 60mph in 4th braking to 20mph in say S4 and pressing on....I would brake hard and downshift as the revs dropped through 1500rpm - smooth as you like.

[Edward]

S5 coupled with downshifts in the higher RPM range (ones that result in the blip taking you up past 4500 rpm) will usually be the most predictable and smooth despite the loud noise and overall seemingly aggressive nature of driving this way.

The worst jerky and lurching downshifts are the ones where you're already coming to a slow speed and still decide to downshift to engine brake. When the car doesn't have a lot of forward momentum, the effect the engine internals has on that momentum is far greater and so it causes the lurch.

The way I see if, the more aggressively you are trying to move gears downward, the more it benefits you to actually be driving in a way that warrants those downshifts.

[M3lbournE92]

Get the gts or euro DCT software and 90% of all of your problems will be solved!

[cw128]

I'm in the UK so presumably I already have the euro DCT software, but I'll take it to my local BMW dealership and see if there is any kind of update they can do to it

[e46m3to135i]

Originally Posted by cw128

Thanks, good to know I'm not the only one that found it annoying at first then and that its perfectly normal. You mention that you were "driving it wrong" but how do you drive it right to avoid having to change how hard you're braking 3 times every time you change down a gear whilst braking? Regardless of which D or S mode I have it in I seem to get the same effect.

What does the GTS flash do then?

Originally Posted by socalm3lover

I have never noticed this. I suspect it has a lot to do with your DCT mode, I am always either in S5 or D5.

I would also like to know what the GTS flash does?

John

Check out this thread:
http://www.m3post.com/forums/showthr...&highlight=GTS

Alex can also flash the most up to date DCT software if you think your on an older version and your dealer refuses to update for you.

His customer service is outstanding and his prices are unbeatable.

-Nick

[Sandye90m3]

One thing that I felt helpful was to downshift at the 2k RPM, anything below that the car will think you are approaching a stop a sign and will begin to engage the clutch, which is not what you want.

If you just want a smooth slowing down, downshift at a minimum of 1900RPM or, let the car put the clutch in at whatever gear you are in and do multiple shifts down.

[e1000]

Originally Posted by M3Now!

Not to rehash this argument (and I drive a DCT). But it IS an automatic transmission, it just uses clutches vs. a torque converter, and has a manual mode. If you set it to D, it WILL shift automatically.

Actually, a traditional automatic transmission has both a torque converter AND planetary gears. DCT uses clutches (two), and synchromesh gears just like a manual transmission.

[gatorfast]

Originally Posted by e1000

Actually, a traditional automatic transmission has both a torque converter AND planetary gears. DCT uses clutches (two), and synchromesh gears just like a manual transmission.

But it shifts automatically for you hence being an automatic transmission.

[cw128]

Originally Posted by gatorfast

But it shifts automatically for you hence being an automatic transmission.

Yeah exactly. That's why I called it an automatic originally, because in my opinion if it changes gear without you touching anything then it is an automatic. I'm well aware that a dual clutch system is not the same kind of automatic as the "old fashioned" style automatic that just has one clutch but to me it is still an automatic. Anyway it is kind of pointless arguing about it

[cw128]

Originally Posted by Sandye90m3

One thing that I felt helpful was to downshift at the 2k RPM, anything below that the car will think you are approaching a stop a sign and will begin to engage the clutch, which is not what you want.

If you just want a smooth slowing down, downshift at a minimum of 1900RPM or, let the car put the clutch in at whatever gear you are in and do multiple shifts down.

Yeah I am normally changing down when quite a bit higher than that, as I'm talking about fairly hard braking during "spirited" driving so the revs are fairly high. Personally I find that the higher the revs are when I down shift then the harsher the engine braking is, and therefore the less smooth the braking is (because there's suddenly a load of engine braking slowing the car down on top of me pressing the brake pedal). I noticed that if I let the revs drop lower before down shifting then it seems a bit smoother (which seems to contradict what people are saying here, unless I'm misunderstanding) so that's kind of a workaround for now... but I can't do that if I do actually want to stay in fairly high revs in the gear that I'm changing down into.

[cw128]

Originally Posted by e46m3to135i

Check out this thread:
http://www.m3post.com/forums/showthr...&highlight=GTS

Alex can also flash the most up to date DCT software if you think your on an older version and your dealer refuses to update for you.

His customer service is outstanding and his prices are unbeatable.

-Nick

Thanks but I'm in the UK so I can't get him to do anything (I doubt he would fly to another country for $60 ) but the GTS flash that is mentioned in that thread does sound good. I especially like the fact that it apparently makes reverse engage pretty much instantly, as I find it very annoying that there's always a couple of seconds delay between putting it in reverse and it actually starting to move backwards. I'm guessing this GTS flash is not something a dealership would do though, but I'll still go see them and see if they have any updates they can do anyway.

[e46m3to135i]

He does the coding remotely through a program interface. All you have to do is purchase a coding cable that costs about $30 dollars:

http://www.ebay.com/itm/US-Seller-Fo...item4aca807cea

Once you receive the cable, contact Alex via PM with your coding request and he'll set up an appointment for you.

[Sandye90m3]

Originally Posted by cw128

Yeah I am normally changing down when quite a bit higher than that, as I'm talking about fairly hard braking during "spirited" driving so the revs are fairly high. Personally I find that the higher the revs are when I down shift then the harsher the engine braking is, and therefore the less smooth the braking is (because there's suddenly a load of engine braking slowing the car down on top of me pressing the brake pedal). I noticed that if I let the revs drop lower before down shifting then it seems a bit smoother (which seems to contradict what people are saying here, unless I'm misunderstanding) so that's kind of a workaround for now... but I can't do that if I do actually want to stay in fairly high revs in the gear that I'm changing down into.

So the free-wheeling only happens when the clutch is engaged and the car is blipping the throttle.

This is the same thing that happens in a manual transmission car when we want to heel and toe. So I'm not to sure what you are trying to correct in your driving as the problem that you are having is the norm of all spirited driving. The clutch will need to be engaged in order for downshifting and that will obviously cause free-wheeling because clutch engagement does not have the same resistance force as a clutch-disengagement in gear.

I'm sure you know what I listed above, but just wanted to make sure that you know you don't have anything to worry about. The only thing I can consider is upgrading your DCT software and engine software, which will make things a bit smoother and a little more aggressive

[pkimM3r]

Technically speaking. Its not a conventional torque converter automatic but it is a dual clutch automatic. It has the ability to shift automatically.

Automanual??

[eternallx]

Originally Posted by Sandye90m3

So the free-wheeling only happens when the clutch is engaged and the car is blipping the throttle.

This is the same thing that happens in a manual transmission car when we want to heel and toe. So I'm not to sure what you are trying to correct in your driving as the problem that you are having is the norm of all spirited driving. The clutch will need to be engaged in order for downshifting and that will obviously cause free-wheeling because clutch engagement does not have the same resistance force as a clutch-disengagement in gear.

I'm sure you know what I listed above, but just wanted to make sure that you know you don't have anything to worry about. The only thing I can consider is upgrading your DCT software and engine software, which will make things a bit smoother and a little more aggressive

This. If you knew how to Heel toe properly before having DCT its the same feeling.

[e46m3to135i]

Originally Posted by Dashman

lol

Name another "automatic" transmission that has clutches instead of a torque converter besides a DCT. I guess if we put a torque converter in a manual gear box it would still be a manual right?

This has been debated numerous times. Depends on how you compare them. Logic vs mechanics.

I'm not going to argue with anyone on here about it. Its a waste of time.