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01-04-2010, 09:54 PM | #1 |
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Tell me more about DCT
Hello,
Ive been in the market for a BMW 135i for a while. Havent bit the bullet for a number of reasons, but Ive been tracking things... Interesting news that 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? Im sure repairs are expensive, and there is lots of fluid replacement if it is anything like what Ive heard of the VW DSG - fluid costs aside, Im mainly interested 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! |
01-05-2010, 11:03 AM | #2 | |
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01-05-2010, 11:52 AM | #3 |
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Considering the high percentage of AT 135s d/cing that option could create problems.
I would love the DCT choice but my wife does use the car on occasion and she prefers the non involvement mode of driving. She does like powerful cars but that is where her involvement starts and ends. |
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01-05-2010, 02:54 PM | #4 | |
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A dual clutch trans can operate in FULL automatic mode where you simply select "drive" and go. You don't need to worry about stop and go traffic and how long you've been on the brakes or anything like that, well, at least that's how it's been for the current crop of DCT's from VW and Mits. If BMW doesn't do something hair-brained to mess up a good thing, minimal driver involvement is all that will be needed to use it. For those want some involvement the DCT will operate pretty much the same as the Sportronic trans does now. If you want manual mode you can have it, and you can select gears with either the console lever or the paddle shifters. How far to redline or near redline the system will allow before doing an automatic upshift is up to BMW. I hope the system will allow full up to the limiter performance without upshifting for us. The main problems with DCT's is how smooth or unsmooth they can be in stop and go traffic where a manual driver will typically need to slip the clutch in order to stay with traffic and do it smoothly. The Audi/VW DSG has had some unsmooth or harsh operation in heavy stop/go traffic where the clutch's get warm, and there can be a bit of lag on take off on some cars when trying to take off slow and smooth. Clutch heat is one issue, and smooth clutch application via software is another. Still, overall I find these transmissions to be really cool and quite smooth for what they do. A torque converter can take up much more shock than a DCT as the TC has fluid to help dampen engine to trans shock, whereas a DCT is a standard clutch operated trans where the clutch is operated by electronics, but it's still a "hard" connection between engine and trans. But, to me that's what makes if feel more like the real thing. |
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01-05-2010, 05:36 PM | #5 |
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I just got out of a GTi with DSG. Originally I wanted a stick but after one driveI was really impressed. It really is faster than a stick if you floor it. It shifts up like silk. Amazing.
After about 10 minutes of owning it you start to hate it. Don't get me wrong, in traffic it's great so if you commute a lot in traffic then get one. As soon as you're on your own on open roads you'll hate it. It's never quite in the right gear: D would shift up too early, sport would go to redline and there's no 'sporty' inbetween. Powering out of corners it would gulp for air because it was never ready to shift down: it would be in 3rd with 4 selected, when you wanted 2, so you get air while it pops down from 4 to 2 on the one clutch. I couldn't wait to get rid of it. If you like to drive, then don't get one. If you want to drag race then fine. It's also notchy on the way down under braking: it shifts down, does nice rev matching but still manages to be bumpy, so no smooth decel. That also used to get to me. I never ever put it in neutral at the lights: thats just garbage. Hope that helps. I'm much happier with a stick. I think DSG is a step up from slushbox: faster, more economical but it won't replace a real clutch for me at least. |
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01-05-2010, 06:44 PM | #6 |
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Funny how all these slushbox "improvements" are in an attempt to make the experience fun. Then again you could save the cash with improved reliability and buy the benchmark 6mt.
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01-05-2010, 07:05 PM | #7 | |
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If you think a DCT is a slushbox, you either don't know what the term means, or don't understand how they work. |
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01-05-2010, 07:16 PM | #8 |
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$.02 worth
if you are really interested in dct, just go to the lively discussion on the m3 boards...
but...we had an audi a3 dsg for 3 years, my wife's daily driver. She never knew what those things behind the wheel were for (paddle shifters). Almost everytime I drove it, I would put it in manual mode for approximately 3 minutes, when I got bored and put in D or S (auto modes). S made great sounds on downshifting, but wasted gas. A couple of times I went into the Malibu canyons, though, and then it was fun. I played with left foot braking, trail braking (it's harder to spin a noseheavy frontdriver) and shifting with paddles (like GT5 or Forza). I now know why some fast autoxers have autos...I also fried my brake pads. No, seriously, if you change the way you drive fast, the paddles are awesome. They probably are the future. But I suspect most people will leave it in auto soon after they take delivery. |
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01-05-2010, 07:29 PM | #9 |
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isn't a DSG different than a DCT? old M3 used to have a DSG everyone hated kinda thing?
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01-05-2010, 07:39 PM | #10 | |
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Yeah, they're different. The SMG used a single clutch, and was really just sort of an automated manual transmission, except you couldn't skip gears. When it does a gear change, it's much the same process as a manual: Clutch in Select Gear Clutch out With the DCT, there's two shafts (one takes care of odd numbered gears and the other takes care of even) and two clutches. The gear selection takes place while the other shaft is engauged, so when it's time to shift, it simply switches shafts. That makes it extremely fast. I'd have to test drive one before I'd jump on it, but I'd certainly consider it. The real issue with them, as mentioned above, is making them smooth around town, where it's constantly engauging and disengauging the clutch. A good manual driver can modulate the gas and clutch to keep from jerking the car around in traffic, and that's something that's pretty hard to program. Last edited by jeremyc74; 01-05-2010 at 10:09 PM.. |
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01-05-2010, 07:42 PM | #11 |
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IMO it is not an auto, but rather a manual w/out a clutch pedal!
It is one of my favorite tranny's w/out a doubt. To bad it will not mate-up to x-drive... |
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01-05-2010, 07:57 PM | #12 | |
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01-05-2010, 08:01 PM | #13 |
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01-05-2010, 08:07 PM | #14 | |
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01-05-2010, 08:17 PM | #15 | |
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I'm not sure I understand where the loss of control is? The only real reason to skip gears going up or down in a manual transmissioned vehicle is just so you don't have to operate the clutch more often than needed. This is taking care of that for you, so why would you want to skip them? |
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01-05-2010, 08:21 PM | #16 |
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JHRZ2 go and test drive a used VW gti with DCT. Play with it and see if you like it. The word on the street is the VW is a fantastic trans. They have got it "right". As for the BWM being new, I wouldnt touch it with a 10 ft pole. Something like that, i would wait a year or 2 to be safe.
As for the trans is a manual with out a clutch pedal. no ATF fluid and NO power sapping converter. THe down side its way to complex with more parts...etc. So, at the end of the day, good ol' Manual is still the king IMHO
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01-05-2010, 08:26 PM | #17 | |
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01-05-2010, 08:31 PM | #18 | |
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You still get to choose exactly which gear you want to be in. If you want to go from fourth to second, tap it twice. It's really not a big deal. In that situation using a manual, why would you skip 3rd if it's not about just not operating the clutch an extra time? Just about every bike on the road today is running a sequential box that requires the same thing. |
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01-05-2010, 08:40 PM | #19 | |
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01-05-2010, 08:40 PM | #20 |
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I will go test drive a VW with DSG, as we are in the market at some point for a jetta diesel wagon...
That said, I have 120k miles on my original clutch in my 91 318i, and I have driven that in a LOT of traffic... it is great in traffic. My wife's old integra was terrible... it seems that BMW is an OK traffic MT... Though Ill try to simulate that on a test drive I guess. Sounds like the MT is still for me, which is exactly what I anticipated... since the MT will still be there on a MY11, Im happy. Seems that the clutch heating mentioned above is due to drivers NOT putting the trans in neutral, and thus the clutch sitting at the bite point too much/too long. Maybe there is truth in the wiki write-up? I always put my slushbox ATs in neutral when stopped or coasting to a stop in traffic... Thanks! |
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01-05-2010, 09:55 PM | #21 | |
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The reason the dual clutches are so fast and smooth is because they preselect the next gear on the opposite clutch (or something equivalent) and just switch seamlessly. Things aren't so fast when you go two gears up or down (same clutch). Trust me, though...dsg on audi will go from 6-3 with 3 tugs on the paddle quite quickly. I used to purposely lift the throttle on upshifts just so I could feel the engine pull between gears, otherwise it was just seamless power delivery. As good as any automatic, better than my experience with smg (just a couple of days). I don't know why i am so vocal on this, maybe i am just excited because i actually have some experience on something on this forum.!! |
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01-05-2010, 10:06 PM | #22 |
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