operating a DSG/DCT dual clutch transmission

[JHZR2]

Hello,

Ive been in the market for a BMW 135i for a while. Havent bit the bullet for a number of reasons, but just got word that it looks like the 2011 model will have a 7-speed DCT.

Im a die-hard MT fan, and really do not like ATs at all. However, 7 speeds and continuous forward momentum with a turbo engine (so there are no pressure variations during shifts) is a good thing... Not that I drive hard - Id drive the thing super-gently 99.9% of the time.

Anyway, I initially dismissed the DCT as more or less an automatic. It only has two pedals, and you can put it in "D" and just turn the brain off... but can you?

Reviewing how to operate the DSG at wikipedia (FWIW):
http://en.wikipedia.org/wiki/Direct-Shift_Gearbox

I get this:
""N"

N position of the floor-mounted shift lever means that the transmission is in "neutral". Similar to P above, both clutch packs and all gear-sets are fully disengaged, however the parking lock is disengaged. This position should be used when the motor vehicle is stationary for a period of time, such as at red traffic lights, or waiting in a queue of stationary traffic.[19] The DSG should not be held in any of the active gear modes while stationary using the footbrake for other than brief periods - due to the clutches being held on the bite point, as this can overheat the clutches and transmission fluid.[19]"

So this tells me that you cannot turn your brain off like with an AT. Or, I guess you can (for a little while), but you will be damaging your gearbox.

So, what's the deal with the DCT/DSG/dual clutch gearbox? You DO always need to be involved for the trans to last? I like that you can set the shifts to firm, and that they will always be correct - seems like a lot less wear that I would put on it, and I am over 120k on my BMW's clutch with city only commuting use... plus there are two clutches, so each one must only get half the use/wear.

That said, it seems that with the clutches always at the bite point, that there is the potential for wear. Plus, I assume there are synchronizers like in a normal MT, right? With the computer always guessing what youre doing next, the minimum number of synchronizations the transmission will be doing is n+1, with n being the number you'd be doing with a normal MT, and with the maximum being a LOT. This equates to me wear and tear higher than a regular MT.

I don't mind fluids... being a bitogger, so long as the service is reasonably DIY, I dont mind servicing the transmission more than necessary... but I do know with the VW DSG that the fluid needs to be done often for good life... that does add a time and cost commitment.

So, besides performance, what do you see as the pros/cons of the dual clutch transmission? fuel economy benefits? a 300k mile city-use clutch? Has anyone heard the cost of replacing the clutches in a dual clutch box?

Im not needy on the constant forward momentum part - fluid costs aside, Im mainly interested in the lifecycle cost benefit to a DCT, if they exist, and if you DO need to ALWAYS be engaged - a "D" position isnt a set and forget position like it is in an AT.

Any comments or ideas? Ive never even driven a VW DSG...

Thanks!

 

[Dieseldoctor]

yah but 20K fluid changes turn me off.. i had a TDI auto it died so trusting they're automatic stuff is hard sell

 

[JHZR2]

But I have multiple MB diesels that have autos that are >200k without rebuiilds... so I can trust standard autos... I just don't like them...

 

[saaber1]

Originally Posted By: JHZR2
Anyway, I initially dismissed the DCT as more or less an automatic. It only has two pedals, and you can put it in "D" and just turn the brain off... but can you?

I can speak only for VW/Audi DSG because i have not driven the BMW. It has three modes, D, S, and M. You can put in D mode and turn your brain off. D is fuel miser mode and it will short shift and keep everything very mellow.

In S mode it will drive extremely aggressively if you get on it. I mean it will push the traction control often and shift past the redline on every shift if you stand on the gas and it will downshift aggressively, always keeping you in the high rev band. I don't use S that much because you can spin the tires so often. But man it shifts absolutely perfect for performance driving.

M is the most fun because you can shift on the steering column or floor shifter by a simple press forward or backwards. The shift is instantaneous. I used to watch touring car racing back when audi was using their early DSG-type boxes. I was blown away by how fast they could shift when braking hard coming into a corner. 4 shifts in a heartbeat is nothing for the DSG.

Think of shooting a .22 caliber semi -auto rifle. It is just like that if you are coming fast into a turn and need to downshift three gears (it's always sequential, can't skip gears). It is absoultely amazing. You can't turn your brain off in M, it will prevent you from going way over redline (it will downshift at that point) and it will prevent you from stalling the car (it will upshift at that point) but that is all.

The D or S options are very nice when you are stuck in traffic.

Re: the wiki thing, for DSG it prolongs the wet clutch life if you use the e brake when starting on a hill, just like a manual. But you don't have to use the e brake to start on a hill at all if you don't want to. F.e. wife never does, I always do. Similar to a manual really except that DSS has some forward creep on flat ground and less backroll on a hill compared to a MT which of course is free-wheeling with clutch in.

Originally Posted By: JHZR2
So, what's the deal with the DCT/DSG/dual clutch gearbox? You DO always need to be involved for the trans to last?

No. I don't think wear of the wet clutches will be an issue.

Originally Posted By: JHZR2
... This equates to me wear and tear higher than a regular MT.

I think the computerized brain is the thing that makes it more of a concern than the clutches in comparison to a MT.

Originally Posted By: JHZR2
I don't mind fluids...

DSG service procedure is almost identical to the procedure for my 95' 740. In fact I am considering using the same DIY fill tool for both.

Originally Posted By: JHZR2
So, besides performance, what do you see as the pros/cons of the dual clutch transmission?

Driving feel. That is most of the attraction for me. I drove both and the DSG is part of the reason why my little GTI makes me smile almost every day. The other reason is that my wife hates a MT. I love a MT. DSG satisfies both. Other benefit is you can turn your brain off when you want and drink coffee, relax, or not wear out your clutch in stop and go traffic.

Originally Posted By: JHZR2
fuel economy benefits?

DSG is only a little better than MT, not enough to be a factor IMO.

Originally Posted By: JHZR2
a 300k mile city-use clutch?

Personally I don't think the brain will last that long. I assume it will have similar life to an AT due to complexity. VW had a temperature-related issue with a teflon coated bushing on some models. In response to complaints, they extended warranty to 100k or 10 years. I am glad to have that extension but my DSG has never missed a beat in 23k miles.

Originally Posted By: JHZR2
Im not needy on the constant forward momentum part - fluid costs aside, Im mainly interested in the lifecycle cost benefit to a DCT, if they exist, and if you DO need to ALWAYS be engaged - a "D" position isnt a set and forget position like it is in an AT.


D and S are set and forget. M is not, You have to tell it when to shift in M. You can also buy 3rd party software for totally removing computer control for things like making it hold in gear past redline etc. for those that are into that.

I would suggest driving both and if the driving dynamics, stuck in traffic factor, and o.k. for non-MT drivers factor do not seem that big of a deal, I would go with the MT. If you like those other factors, the DCT may be the way to go. The driving experience seals the deal for me. I feel like one of those touring car racers or f1 racers driving that thing sometimes ha ha.

I would expect life comparable to an AT however, not as long as a MT, but that is only a gut feel and the assumption I went on when buying my DSG. I am referring to life of the brain not the clutches. I do think the clutches will last much longer than a MT clutch. But that is also an assumption as I haven't driven it long enough to know from experience.

-----------------------------------------------More info. from another DSG post here:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1383359

Have had my 6 speed DSG (VW GTI) for seven months now and I use manual mode all the time except when I need my hands free for something important like drinking coffee ha ha or when stuck in traffic.

The manual mode is just so much more fun and you can keep the revs right where you want them all the time. On downshifts it rev matches perfectly and the shifts are pretty much instantaneous. Have always been a manual tranny guy but this DSG is just incredible.

BTW keeping it in the automatic sport mode is not too bad either although I prefer manual mode. In "s" mode the car lives in the high rpm range and downshifts aggressively. When accelerating hard, it shifts just past the redline. Amazing.

Some old DSG videos/articles for those interested. Hope these links still work.

7 speed dry clutch dsg http://www.youtube.com/watch?v=WVWP7TYhP0c&feature=related

Good article but some mistakes in it http://blogcritics.org/archives/2006/11/08/091620.php

Jason Plato of Fitth Gear test drives the dsg (about 1:15 into the video is where good dsg discussion starts) http://www.youtube.com/watch?v=5EdjEE0edPw

test of manual vs dsg gti http://www.youtube.com/watch?v=gmMNRQ1GJ3o

 

[Audi Junkie]

The Audi guys love them.

 

[rjundi]

Given BMW and VW and transmission makers have limited experience with this type of gearbox in consumer grade vehicles I would be cautious and make no predictions on reliability. I think it is something you try out and either like or dislike as a overall package. I did not mind but was a bit bored driving the DSG GTI. I hated the DSG Jetta TDI.

 

[oliver88]

I absolutely love my Audi A3 3.2 litre with DSG...single best car I've ever owned and one of the most fun and rewarding cars to drive as well. I have about 30,000 miles on it and need to get the tranny fluid changed soon.

 

[Quattro Pete]

Originally Posted By: rjundi
I hated the DSG Jetta TDI.

Can you expand on this?

 

[JHZR2]

+1

 

[CATERHAM]

Since I spent a life time mastering "heal and toe" down shifts to the point that it is now "automatic" in cars with proper pedal placement, I lament the arrival of the DGG gearboxes.
At track days it certainly used to separate the "real drivers" from the posers.

BTW in the 135i, how much more of an option is it over the 6-speed manual?

 

[440Magnum]

Originally Posted By: JHZR2
But I have multiple MB diesels that have autos that are >200k without rebuiilds... so I can trust standard autos... I just don't like them...


Chrysler 727, GM TH400, Ford C6... all 200kmile plus automatics 30 years ago. Modern 5- and 6-speed autos are more of a mixed bag with some being on the fragile side, but there are some brutally reliable ones out there too. Its really gotten to the point that *most* automatics (with some notable exceptions) will go repair-free longer than a manual in the same application simply because the clutch eventually has to be replaced and that requires dropping the manual trans out of the car.

IMO, the DSG/DCT is just another automatic. No clutch pedal => automatic. Yes, you can flip paddles to upshift/downshift, but you can do that with properly equipped conventional torque convertor/planetary automatics too. BFD. About all you can say is that the DSG/DCT responds to the paddle input more quickly.

I love stirring gears, don't get me wrong. I'm just saying part of stirring gears is the dance you do with BOTH feet, not just the right one.

 

[d00df00d]

AFAIK, the biggest benefit to a DSG over an automatic is that there is virtually no interruption of power during shifts. That reduces drivetrain shock and can be a big help in sporting applications because it greatly reduces the chance that a mid-corner shift will destabilize the car.

 

[ffracer]

Originally Posted By: d00df00d
AFAIK, the biggest benefit to a DSG over an automatic is that there is virtually no interruption of power during shifts. That reduces drivetrain shock and can be a big help in sporting applications because it greatly reduces the chance that a mid-corner shift will destabilize the car.


Mid-corner shifts are never needed. Braking was not done properly - either too late or too early to be worth the instability in shifting udring cornering.

 

[JHZR2]

Originally Posted By: CATERHAM


BTW in the 135i, how much more of an option is it over the 6-speed manual?


Don't know yet, but I believe it is $2700 in the M3.

 

[JHZR2]

Originally Posted By: 440Magnum

IMO, the DSG/DCT is just another automatic. No clutch pedal => automatic. Yes, you can flip paddles to upshift/downshift, but you can do that with properly equipped conventional torque convertor/planetary automatics too. BFD. About all you can say is that the DSG/DCT responds to the paddle input more quickly.




while the shifts CN be automatic, it IS a manual transmission design inside, FWIW.

 

[d00df00d]

Originally Posted By: ffracer
Mid-corner shifts are never needed. Braking was not done properly - either too late or too early to be worth the instability in shifting udring cornering.

I think we both know that the right thing to do and what people often do are rarely the same.

Besides, people make mistakes. With a good DCT in a properly sorted car, you have more room for error. That's never a bad thing (although relying on it obviously is).