DCT Clutch Problems - Page 4 - BMW M5 Forum and M6 Forums
F10 M5 Discussion 2010- Discussion about the next upcoming generation M5 based on the next generation 5-series, the F10.

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post #31 of 54 Old 4th July 2016, 10:17 AM
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So you change down, the revs rise to match the new gearbox speed, and the revs stay high. Surely they would do, unless you actually change the speed of the car? I don't doubt you have an issue here, I'm just being a bit slow at grasping it - apologies.

There's a few things I can't get my head around, and was hoping you could elaborate on: How do you know the clutches have dis-engaged or re-engaged? Isn't the point of a DCT that one of them is always engaged? Does the software you used to analyse this tell you which of the two clutches is being used to transmit power at any moment? And therefore, is it always the same one 'failing'? Also, which gears does this happen in? Again, apologies if I have completely misunderstood the concept of a DCT gearbox. Perhaps someone could enlighten us?

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post #32 of 54 Old 4th July 2016, 06:16 PM Thread Starter
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Quote:
Originally Posted by 100%Cocoa View Post
So you change down, the revs rise to match the new gearbox speed, and the revs stay high. Surely they would do, unless you actually change the speed of the car? I don't doubt you have an issue here, I'm just being a bit slow at grasping it - apologies.
After manually down shifting rev matching occurs and initial engine braking begins. After about 1 second engine braking ceases and revs stay elevated. F10 is coasting with clutches disengaged and Valvetronic keeps racing at rev match rpms. Watched the clutch operation do this while using Rheingold BMW diagnostic software.

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There's a few things I can't get my head around, and was hoping you could elaborate on: How do you know the clutches have dis-engaged or re-engaged? Isn't the point of a DCT that one of them is always engaged? Does the software you used to analyse this tell you which of the two clutches is being used to transmit power at any moment? And therefore, is it always the same one 'failing'? Also, which gears does this happen in? Again, apologies if I have completely misunderstood the concept of a DCT gearbox. Perhaps someone could enlighten us?

Thanks,
Barney.
Rheingold allows you to monitor what the DCT clutches are doing. I was driving and George Boutsikos was monitoring Rheingold on his lap top. His observation was that both clutches were disengaging during our testing. It would be the equivalent of what happens when stopped at a traffic light or putting the DCT in neutral.
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post #33 of 54 Old 5th July 2016, 03:01 PM
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Hey Ray,

It would be interesting to see, therefore, if you let off the throttle at 60 MPH in 7th and time the deceleration to about 40 MPH....and then do the same from 60 MPH again but immediately downshift to 5th and time deceleration to 40 MPH.

Or even just do it in directly in 5th from 60 MPH down to 40 MPH and compare it to doing it in 7th. You seem to suggest that your car is coasting in gear (clutches disengaged) when 'off throttle'.

According to what you have said, all times should be about the same (save for the initial engine braking of about a second or so when you make a downshift) if the clutches disengages when the throttle is released in gear ?

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post #34 of 54 Old 6th July 2016, 04:41 PM
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I'd like to understand how these 'wet' clutches work to really understand what's going on here. I read a bit and I'd never realised just how like an automatic gearbox a DCT is. You never get much engine braking with a traditional auto. Combine that with low compression and you're going to struggle to get much at all - as I find on a daily basis. When the software says the clutches are disengaged, exactly what do they mean? It's not as black and white as a dry clutch...... Can the Rheingold guy offer any insight?
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post #35 of 54 Old 15th July 2016, 10:29 AM Thread Starter
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I'd like to understand how these 'wet' clutches work to really understand what's going on here. I read a bit and I'd never realised just how like an automatic gearbox a DCT is. You never get much engine braking with a traditional auto. Combine that with low compression and you're going to struggle to get much at all - as I find on a daily basis. When the software says the clutches are disengaged, exactly what do they mean? It's not as black and white as a dry clutch...... Can the Rheingold guy offer any insight?
When I first leased my F10 the DCT functioned perfectly in all modes including manual downshifts and engine braking. BMW won't admit it but I'm certain this new behavior is the result of their tinkering with the software. It's no longer fun to drive; might as well get a 7 Series. In addition to the engine braking issue, the F10 frequently maintains highway speeds for protracted periods after taking your foot off the accelerator pedal (think cruise control engagement) which is an even more dangerous situation. This is why it's going back to BMW when the lease ends in October. George Boutsikos at M-Chanics can give you more detail on the tests we conducted.
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post #36 of 54 Old 20th July 2016, 08:05 PM Thread Starter
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Lightbulb Mystery Solved?

Beginning in 2014 BMW installed a "sail/cruise" feature on vehicles with automatic transmissions to improve fuel economy. It is part of Eco-Pro mode. When cruising at speeds of 30 mph to 100 mph in this mode, taking your foot off the accelerator disengages the transmission from the engine and the vehicle coasts. This is a known phenomenon on Boards other than the M5.

Found out about this serendipitously while reading an article about the 2016 7 Series where they were extolling the sail/cruise feature. Supposedly this feature can be turned off through the I drive controller. I will explore this on the coming weekend when we'll be going on a drive.

This alleged feature should not be on an M5 IMHO.
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post #37 of 54 Old 28th July 2016, 02:00 PM
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Beginning in 2014 BMW installed a "sail/cruise" feature on vehicles with automatic transmissions to improve fuel economy. It is part of Eco-Pro mode. When cruising at speeds of 30 mph to 100 mph in this mode, taking your foot off the accelerator disengages the transmission from the engine and the vehicle coasts. This is a known phenomenon on Boards other than the M5.

Found out about this serendipitously while reading an article about the 2016 7 Series where they were extolling the sail/cruise feature. Supposedly this feature can be turned off through the I drive controller. I will explore this on the coming weekend when we'll be going on a drive.

This alleged feature should not be on an M5 IMHO.
Any (fuel injected) engine will use zero fuel when coasting on a closed throttle, (ie. lifting off whilst in gear in a manual car) and 'some' fuel when coasting on an idling throttle (ie. clutch pushed in on a manual car). The car is also under less control and so is less safe. On top of that, you refer to your revs staying high, which would surely always use more fuel than either scenario I mentioned above. I can't believe BMW would introduce such a feature, but then I have been wrong before....??
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post #38 of 54 Old 28th August 2016, 01:38 AM Thread Starter
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I agree it makes no sense at all. BMW NA screwed the pooch with my Drivelogic. Glad I am returning it to them on 10/18/16. I am through with BMW for the foreseeable future
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post #39 of 54 Old 28th August 2016, 12:06 PM
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post #40 of 54 Old 30th August 2016, 09:44 AM
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As above. Sounds like you had a dick head dealer. Most of us have had more positive experiences.

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