DCT Longevity and Maintenance

[xman11]

For those of you who own DCT or have knowledge on how they are maintained, would you please respond to the questions below?
I'm trying to decide if DCT is worth keeping outside of warranty.
I did a search and most threads are endless 6MT vs DCT discussions.

Answers based on direct experience would be best, but given the newness of DCT, speculative responses would be fun for discussion.

1) What's the expected life of the DCT when driven mostly on the street with the occasional launch? About the same as a manual, or more, considering there could be less clutch slippage wear due to a wet clutch and more precise downshifts.

2) What's the cost of maintaining the DCT outside of warranty?
a) Change out fluids - I've heard service on a GT-R runs about $2k, of which $1K is the cost of the fluid.

b) Replacing the clutch - Someone mentioned that once the clutch pack wears out, that the entire tranny needs to be replaced, approx $10k price tag.


Thanks in advance.

[Lemans_Blue_M]

Well it's funny you should ask this, because this was a major concern of mine as well.

I asked one the powertrain gurus at the M division this question in the summer of 2008.

He told me since the shifts are all controlled by the M-DCT computer module, it functions more like a conventional automatic transmission does. Not exactly the same, but very similar in some respects. He also avoided answering my question about the potential lifespan of such a technically advanced transmission. (at first)


After a few minutes I asked again and he reluctantly said he (nor anyone else) could answer that question beyond a reasonable doubt. There are too many variables to give any definitive answer.

The only thing I could get out of him was the theoretical "best case scenario" if the car was driven 'normally', and not by some hot dog who thinks the street is there own private drag strip.

In that best case scenario, factoring in the torque limit and the power output of the S65B40 engine, the expected lifespan could reach 200,000 miles before it would need to be replaced.

The wet clutches may need to be serviced before that point (in some cases) but here's the problem...there are no aftermarket parts available to fix these transmissions. (on the open market)

If you wanted to repair your M-DCT transmission, you are out of luck. You cannot repair these dual-clutch transmission like a conventional manual clutch transmission. The only way the DCT can be repaired, is to return it to an authorized Getrag service center that has the parts necessary to rebuild it. Period.

That's your only option, besides purchasing a rebuilt replacement sold through the BMW dealership's parts dept.

If this ever becomes necessary (out of warranty)...

The replacement cost for the M-DCT transmission (sourced from Getrag) is:

6,078.01 Euros = 8,905.53 US Dollars

Labor charges will almost certialy push the total price over the $10,000 mark.

The good news is...you shouldn't think of the M-DCT as a more advanced MANUAL transmission, but rather a more complex AUTOMATIC transmission.

The computer decides when to shift (and at what rpm), so any potential abuse or damage is limited by the pre-programed software operating system. This software controls every aspect of the dual clutch transmission. (even in the MANUAL mode)

If you make an ill-advised gear selection choice (that will cause damage to the transmission or the engine), the computer will simply disregard your request and/or take over to fix the error. (unlike a 'true' third-pedal manual transmission that has no such backup system in place)

A properly maintained automatic transmission will last a very long time by observing the proper oil drain intervals.

BTW: I was told that our M-DCT transmissions would benefit from tranny fluid flush every 40k, despite the company's "lifetime fill" BS on this type of gearbox.

[Dascamel]

So 10k for a new tranny eventually and possibly 2k every 40k miles for a fluid flush? Not sure about you guys, but I'm not changing the fluid until the price comes down to earth, if it ever does.

[Lemans_Blue_M]

Originally Posted by Dascamel

So 10k for a new tranny eventually and possibly 2k every 40k miles for a fluid flush? Not sure about you guys, but I'm not changing the fluid until the price comes down to earth, if it ever does.

If you get a M-DCT transmission fuild flush at the dealership, it will likely run you 300-400 bucks...not 2k.

[Dascamel]

Originally Posted by Lemans_Blue_M

If you get a M-DCT transmission fuild flush at the dealership, it will likely run you 300-400 bucks...not 2k.

How hard is it to perform the flush?

[Lemans_Blue_M]

Originally Posted by Dascamel

How hard is it to perform the flush?

Well, you can't actually do this in your garage at home, so you need to let the dealer perform this task.

There is a special procedure, equipment, and oil used to perform the flush.

It is very important that to no air gets into the system. The DCT transmission functions as a closed-loop hydraulic unit. Changing the fluid is not a DIY project.

[Dascamel]

Originally Posted by Lemans_Blue_M

Well, you can't actually do this in your garage at home, so you need to let the dealer perform this task.

There is a special procedure, equipment, and oil used to perform the flush.

It is very important that to no air gets into the system. The DCT transmission functions as a closed-loop hydraulic unit. Changing the fluid is not a DIY project.

Yeah, thats what I was wondering. Thanks for the reply.

[swamp2]

Some good info LMB. However, I have some points of disagreement.

1. I doubt that gently or normally driven DCTs will only last 200k miles. I think that both Getrag and BMW powertrain engineers can give some very precise information about the longevity of their product but will not do so for legal and warranty liability reasons. Of course that being said all complex products have a statistical lifetime, each will dies a a different use time/mileage based on both use and manufacturing tolerances. Based on the fact that a good old MT can last well over 300k miles and based on the fact that a DCT never slips the clutches and never grinds a gear, I would expect that with the fluid changes (that I know I will be doing) these units could easily last just as long.

2. I don't at all agree that one should think about the M-DCT as an automatic. However, again it comes down to a user interface perspective vs. the basic internal construction and engineering perspective. If you only use the tranny in auto mode I suppose you can choose to call it an automatic. However, on the inside and mechanically speaking it is much much more similar to a good old MT. Other than the complexity of the concentric clutches and concentric shafting the unit IS mechanically simpler than an automatic transmission.

I know I for one will be buying an extended warranty for my car come 50k miles.

[Dascamel]

Swamp, how often are you planning on changing the dct fluid in your car?

[Montoya]

Originally Posted by swamp2

Some good info LMB. However, I have some points of disagreement.

1. I doubt that gently or normally driven DCTs will only last 200k miles. I think that both Getrag and BMW powertrain engineers can give some very precise information about the longevity of their product but will not do so for legal and warranty liability reasons. Of course that being said all complex products have a statistical lifetime, each will dies a a different use time/mileage based on both use and manufacturing tolerances. Based on the fact that a good old MT can last well over 300k miles and based on the fact that a DCT never slips the clutches and never grinds a gear, I would expect that with the fluid changes (that I know I will be doing) these units could easily last just as long.

Don't forget that the DCT has a control unit and other electro-hydraulic components that can be single points of failure down the road. Extra parts statistically will shorten the life of the unit all things equal. Of course as you mention the DCT should enhance the life of the gears and clutch- but is it enough to offset the extra components?

[footie]

I think 200k miles from any Dual Clutch Transmission without needing some form of repair will be highly unlikely. Also I concur with the estimate of £200~300 fluid change when required.

The only thing I am not so sure of is the replacement price, I know VAG charge something like £7500 for a DSG replacement which is nowhere near as complex as the M-DCT so in my opinion BMW will probably charge you closer to £10K over here. Whether Getrag are allowed to sell direct to you is up for debate, I would have thought you would have to go through BMW for that.

[ROTORHEAD77]

I'm pretty sure that these transmissions are rebuildable. I don't think it is going to run you 10 grand.

[SenorFunkyPants]

Its my understanding that the boxes are supplied wet filled to BMW in a sealed for life state. The clutches are more similar to that found in a LSD which are very long lasting units. The only question is on the life of the gearbox oil which is an oil designed specifically for this type of gearbox/clutch. I would have though an oil change at 60,000 miles might be worth while as long as you had confidence that your dealer knew the correct procedure.

[M3WC]

Just buy a new car after 4 years. New M3 will be out anyways.

[Benjjman007]

Originally Posted by JetBlack5OC

Just buy a new car after 4 years. New M3 will be out anyways.

What if they don't want a new car. I for 1 love my M3 and plan to keep it for more than 4 years.

[ROTORHEAD77]

Odds are that the new M3 is not going to have the exotic, high-revving V8. I believe this car is goign to be a sought after car for years to come because of what is under the hood. I plan on saving it for years. BMW's are long-winded cars. They last for 20+ years as daily drivers with only basic upkeep. I hope that I did not make a mistake by choosing the girly transmission in order to attain the WAF.

[gr8000]

Originally Posted by Lemans_Blue_M

If you get a M-DCT transmission fuild flush at the dealership, it will likely run you 300-400 bucks...not 2k.

That's not the info I got from my service tech. Believe it or not, he said that 1 liter of the special DCT fluid costs E1,300!!! Now, I don't know if this is a mistake or some type of BS protectionism for the DCT fluid (so that no-one can have easy access to it and mess around with the formula and oil changes) but this is what I was told and this also apears on paper as the unit cost per litter in my break-in service invoice when they topped up a very small quantity of the fluid in the tranny! It could well be a typo as well but I don't think so.

If it is true, I don't think it will be an easy choice to change tranny fluid every now and then!

Originally Posted by swamp2

1. I doubt that gently or normally driven DCTs will only last 200k miles. I think that both Getrag and BMW powertrain engineers can give some very precise information about the longevity of their product but will not do so for legal and warranty liability reasons. Of course that being said all complex products have a statistical lifetime, each will dies a a different use time/mileage based on both use and manufacturing tolerances. Based on the fact that a good old MT can last well over 300k miles and based on the fact that a DCT never slips the clutches and never grinds a gear, I would expect that with the fluid changes (that I know I will be doing) these units could easily last just as long.

In general yes, but depending on the LC (ab)use and road conditions (read good quality) there may be significant clutch slipage & wear particularly when repeaditly deploying LC. Of course even with the worse absue of the LC, the computer offers adequate protection by turning down more LC requests until the system cools down which definitely helps but I would't say teh DCT never slips the clutches.

Hopefully the DCT will last longer due to the controlled environment it is designed to operate in (as mentioned in more detail in the previous posts) as compared to the manual tranny. However it is not only the well protected / controlled wet clutch pack that contributes to longevity but also the reliability of every other component (and by definition the DCT is a more complex system that the 6MT). I mean it will be great if the clutches last for ever but then if for instance the electrohydraulic clutch acuators fail every 70k miles, then the high pressure lines fail every 100k miles (all these are random numbers & examples) then you get DCT failures which need to be attended as much as clutch changes in the 6MT need to be attended too every now and then. So it is also a matter of definition what is regarded "DCT lifespan" and what "ordinary wear and tear".

Based on the above, whether the DCT will last 200 or 300k miles it remains to be seen but I would personally be positivey surprised if it exceeds 250k miles (=400k km) based on an "average" usage i.e. including some LCs and track usage. And I would definitely expect some form of inbetween failure(s) well before that caused by individual component failure.

[swamp2]

Of course many good points above. Reliability of basic things such as hydraulics, hydraulic connections, fork movement actuators, electronics, etc. are all complexity that will in general lower reliability. gr8000: thanks for the correction about DCT "never" slipping the clutch. That was technically my mistake. What I meant is that outside of launch events and the required infinitesimal slips required when taking off from zero speed, clutch slippage is reduced to practically zero .

[ihyln]

Originally Posted by JetBlack5OC

Just buy a new car after 4 years. New M3 will be out anyways.

BMW will not have a M3 sedan for the next generation. It's either the M5 or RS4 on my list if something happens to my car.

Just a quick food for thought, I know that the SMGII and III are "kinda" automatics like the current DCT and they seem to be holding up well.

[chuckvic]

FYI< Porsche says 911 with DCT equal gets fluid changes I believe every 30K miles, doubt BMW fluid is superior to Porsche.

chuck

[swamp2]

Originally Posted by chuckvic

FYI< Porsche says 911 with DCT equal gets fluid changes I believe every 30K miles, doubt BMW fluid is superior to Porsche.

chuck

Excellent point!

[SenorFunkyPants]

Originally Posted by chuckvic

FYI< Porsche says 911 with DCT equal gets fluid changes I believe every 30K miles, doubt BMW fluid is superior to Porsche.

chuck

BMW don't make the fluid...AIUI its a custom made lubricant made by BP for getrag specifically for their DCT.