DCT issues after servicing - LONG

[Andryuha]

I'll try not to write a novel, but here goes. Last year I picked up an E90 from one of the forum members. The car has been meticulously maintained and came with a complete service history. Since the car had a bit over 100k miles, I decided to do a transmission service (fluid flush, filters, pan). Although everything worked great and the car drove perfectly.

I'm normally a DIYer, but for the sake of saving time and maintaining proper records, I took it to a local Euro shop (Shop 1) that has a great rep. They used LiquiMoly fluid (which I wasn't aware of until after the service. Anyway, after I picked up the car, I've noticed that in the manual mode, the upshift from 3 to 4 was a bit rough from time to time. Since I have not driven the car much up until that point, I chucked it up as normal. I did take it back to the shop that did the service and they stated that the fluid level is normal and deemed the shifting as normal. Eventually the issue seemingly went away.

Fast forward to 3 months later - I can hear a faint whine from the transmission at higher RPMs - 5k+ and when driving aggressively, 3-4 gets clanky from time to time. This time I took the car to another BMW specialist (Shop 2). After looking at it, they stated that there is a leak in the side cover, but they can't tell the reason for the whine. They suggested that I take the car to shop 1, since the leak is coming from the seal that they supposedly replaced. I took the car back to Shop 1 and was informed that the leak is actually coming from the mechatronics unit. They also stated that it's a different fluid than DCT fluid, which alarmed me, since there is no "mechatronics fluid" as they suggested. They quoted me $1800 to drop the transmission and replace the o-ring. Because they really threw me off with the mechatronics fluid talk - I took the car to shop 3 (Porsche and Audi specialist).

Today, I got a call from Shop 3, stating that they drained a bit of fluid and found some metal shavings. Their recommendation - replace the DCT!

Where do I go from here? Cough up the dough and replace the DCT? Fix the leak, do a flush and keep driving? Take it to shop 4 for yet another opinion? The car drives fine, minus the whine and random 3-4 clunk during aggressive driving.

[DrFerry]

Originally Posted by Andryuha

I'll try not to write a novel, but here goes. Last year I picked up an E90 from one of the forum members. The car has been meticulously maintained and came with a complete service history. Since the car had a bit over 100k miles, I decided to do a transmission service (fluid flush, filters, pan). Although everything worked great and the car drove perfectly.

I'm normally a DIYer, but for the sake of saving time and maintaining proper records, I took it to a local Euro shop (Shop 1) that has a great rep. They used LiquiMoly fluid (which I wasn't aware of until after the service. Anyway, after I picked up the car, I've noticed that in the manual mode, the upshift from 3 to 4 was a bit rough from time to time. Since I have not driven the car much up until that point, I chucked it up as normal. I did take it back to the shop that did the service and they stated that the fluid level is normal and deemed the shifting as normal. Eventually the issue seemingly went away.

Fast forward to 3 months later - I can hear a faint whine from the transmission at higher RPMs - 5k+ and when driving aggressively, 3-4 gets clanky from time to time. This time I took the car to another BMW specialist (Shop 2). After looking at it, they stated that there is a leak in the side cover, but they can't tell the reason for the whine. They suggested that I take the car to shop 1, since the leak is coming from the seal that they supposedly replaced. I took the car back to Shop 1 and was informed that the leak is actually coming from the mechatronics unit. They also stated that it's a different fluid than DCT fluid, which alarmed me, since there is no "mechatronics fluid" as they suggested. They quoted me $1800 to drop the transmission and replace the o-ring. Because they really threw me off with the mechatronics fluid talk - I took the car to shop 3 (Porsche and Audi specialist).

Today, I got a call from Shop 3, stating that they drained a bit of fluid and found some metal shavings. Their recommendation - replace the DCT!

Where do I go from here? Cough up the dough and replace the DCT? Fix the leak, do a flush and keep driving? Take it to shop 4 for yet another opinion? The car drives fine, minus the whine and random 3-4 clunk during aggressive driving.

A DCT leaking "O" ring seal is associated with a faint shrill whine that sounds similar to a Dentist's drill as well as slow, seeping DCT fluid. I don't know if it could also be the cause of the 3 to 4 clunk but I'll speculate it might be linked. The "O" ring seal has been successfully replaced by Forum Members without dropping the transmission, though having double jointed fingers apparently helps. All jokes aside I doubt it's necessary to replace the DCT. Search the forum for a DIY on the DCT "O" ring seal replacement. Most synchromesh transmissions have some metal particles on the magnetic drain plugs due the frictional nature of how synchromesh operates. Especially after hundreds of thousands of miles. If the metal particles are large - such as helical gear teeth - then that's a different matter. I recommend replacing the "O" ring seal because that's a known leakage and operation issue. The DCT takes very special OEM Gearbox Fluid. Short term mitigation could be to drive in a higher (or lower) shift logic program to affect the 3 to 4 clunk. Try to discern if there's a better subjective difference in 3 to 4 clunk between S2 and S5 DCT shift logic programs.

[Andryuha]

Originally Posted by DrFerry

A DCT leaking "O" ring seal is associated with a faint shrill whine that sounds similar to a Dentist's drill as well as slow, seeping DCT fluid. I don't know if it could also be the cause of the 3 to 4 clunk but I'll speculate it might be linked. The "O" ring seal has been successfully replaced by Forum Members without dropping the transmission, though having double jointed fingers apparently helps. All jokes aside I doubt it's necessary to replace the DCT. Search the forum for a DIY on the DCT "O" ring seal replacement. Most synchromesh transmissions have some metal particles on the magnetic drain plugs due the frictional nature of how synchromesh operates. Especially after hundreds of thousands of miles. If the metal particles are large - such as helical gear teeth - then that's a different matter. I recommend replacing the "O" ring seal because that's a known leakage and operation issue. The DCT takes very special OEM Gearbox Fluid. Short term mitigation could be to drive in a higher (or lower) shift logic program to affect the 3 to 4 clunk. Try to discern if there's a better subjective difference in 3 to 4 clunk between S2 and S5 DCT shift logic programs.

Thanks! Yes, that's the exact kind of whine that I am hearing - almost like a dentist drill. I do realize that there is a specific fluid for the gearbox, but Shop 1 implied that the mechatronics unit is filled separately with a different fluid. Shop 3 stated that they found "abnormal metal shavings in the DCT fluid".

The clunk is only present on S5. I made an effort to not drive the car as I normally would until the issue is sorted, so I keep it on S3. I should also mention that I have a Dinan tune for the DCT.

[DrFerry]

Originally Posted by Andryuha

Thanks! Yes, that's the exact kind of whine that I am hearing - almost like a dentist drill. I do realize that there is a specific fluid for the gearbox, but Shop 1 implied that the mechatronics unit is filled separately with a different fluid.

The clunk is only present on S5. I made an effort to not drive the car as I normally would until the issue is sorted, so I keep it on S3. I should also mention that I have a Dinan tune for the DCT.

Well let's hope that Shop 1 did not use a different fluid in the mechatronics unit because that would definitely mess things up. The DCT only takes DCT fluid and nothing else.

If S3 helps then also try S2 or Snow Mode S1 - as well as D2 and D3. The Dinan tune is probably not the issue. The leaking "O" ring probably is though. I agree the faint shrill dentist drill type whine is annoying and so is the slow seeping DCT fluid leak but it's not massively urgent to repair immediately. However, the wrong fluid in the mechatronics unit should be ruled out first.

[Andryuha]

Originally Posted by DrFerry

Well let's hope that Shop 1 did not use a different fluid in the mechatronics unit because that would definitely mess things up. The DCT only takes DCT fluid and nothing else.

If S3 helps then also try S2 or Snow Mode S1 - as well as D2 and D3. The Dinan tune is probably not the issue. The leaking "O" ring probably is though. I agree the faint shrill dentist drill type whine is annoying and so is the slow seeping DCT fluid leak but it's not massively urgent to repair immediately. However, the wrong fluid in the mechatronics unit should be ruled out first.

They did not touch the mechatronics unit at the time of the DCT flush. They wanted to do it on my 3rd visit, but I went elsewhere because they obviously had no clue what they were talking about.

[DrFerry]

Originally Posted by Andryuha

They did not touch the mechatronics unit at the time of the DCT flush. They wanted to do it on my 3rd visit, but I went elsewhere because they obviously had no clue what they were talking about.

Here's the link to the DCT O Ring Seal DIY thread. Hope this helps. There's other similar threads out there too. Let us know what you decide to do.

DIY: Fix the DCT Fluid Weeping Problem (Mechatronics Harness O-Ring) https://www.m3post.com/forums/showthread.php?t=1697657

[Andryuha]

Originally Posted by DrFerry

Here's the link to the DCT O Ring Seal DIY thread. Hope this helps. There's other similar threads out there too. Let us know what you decide to do.

DIY: Fix the DCT Fluid Weeping Problem (Mechatronics Harness O-Ring) https://www.m3post.com/forums/showthread.php?t=1697657

Since you've offered so much advice, I figured I would give an update. I talked to the tech and he stated that what he found were metal shavings and not actual pieces of gears, etc. The plan now is to replace the O ring on the sleeve and flush the fluid. The shop that completed the DCT service used Liqui Moly and we will use Pentosin this time around. The mechanic conceded that if it was his personal vehicle, he would do the same thing.

[Helmsman]

Originally Posted by Andryuha

Since you've offered so much advice, I figured I would give an update. I talked to the tech and he stated that what he found were metal shavings and not actual pieces of gears, etc. The plan now is to replace the O ring on the sleeve and flush the fluid. The shop that completed the DCT service used Liqui Moly and we will use Pentosin this time around. The mechanic conceded that if it was his personal vehicle, he would do the same thing.

As stated by Doc, the DCT box use Pentosin DCTF-1 ONLY. I had a dealer filling with ordinary auto fluid a number of years ago, resulted in that they where "forced" by BMW to replace the complete box+cooler. Check out the attachement.

Good luck!

[edycol]

Originally Posted by Helmsman

As stated by Doc, the DCT box use Pentosin DCTF-1 ONLY. I had a dealer filling with ordinary auto fluid a number of years ago, resulted in that they where "forced" by BMW to replace the complete box+cooler. Check out the attachement.

Good luck!

I just can't believe how many people fall on this Liqui Moly Made in Germany garbage (not that it is your fault OP).

[Helmsman]

Originally Posted by edycol

I just can't believe how many people fall on this Liqui Moly Made in Germany garbage (not that it is your fault OP).

No clue how it works but the fluid for the DCT somehow need to both lubricate the moving parts while allow friction for the clutches. Bit of a mystery that one shouldn't break.

[edycol]

Originally Posted by Helmsman

No clue how it works but the fluid for the DCT somehow need to both lubricate the moving parts while allow friction for the clutches. Bit of a mystery that one shouldn't break.

Which is same way as manual transmission fluid works.
Except, DCT is much more complex environment.
VW had issues with their DSG in 2003 and 2004. Solution? Semi-synthetic fluid with different additives to the horror of people who think full synthetic is always solution.
Point: always OE fluid in such complex systems.

[Helmsman]

Originally Posted by edycol

Which is same way as manual transmission fluid works.
Except, DCT is much more complex environment.
VW had issues with their DSG in 2003 and 2004. Solution? Semi-synthetic fluid with different additives to the horror of people who think full synthetic is always solution.
Point: always OE fluid in such complex systems.

Agreed. Reminds me that it wasn't auto trans fluid but standard manual trans fluid that the dealer filled my previous box with. So yes the specific DCT fluid is what counts.

[nyc_dude]

Evolve Automotive cracks open a F8X M3/M4 DCT.

Cheers

[nyc_dude]

So my E9X M3 DCT failed at 170k miles. It cost $14k to replace and install.

Best bet is to get a used low mileage DCT (<60-80k miles) through Deans Bimmer (///M Porium in Texas). They might service it for you first with new seals, filters, fluid...so it is a drop in. Important to synch the ECU and DCT software too to the latest BMW versions.

Depending on the state you live in, you might not find reliable BMW Techs or complex servicing of things like the DCT. Might need a road trip to a reputable shop hundreds of miles away that specialize in ///M cars.

The DCT pan (bottom), mechatronics units (side) and harness o-ring seal (top) are all different. The o-ring leak might not cause any shifting problems, unless you lost a liter or more of fluid.

If the shop has to drop the DCT...service the driveshaft rubber components to get rid of any clunks noises, including the Guibo, Center Bearing, and maybe the rear CV Joint.

Good luck...BMW DCTs are a black hole. BMW Dealerships won't open them up for repairs and rebuilds.


Cheers

[Redd]

Originally Posted by nyc_dude

So my E9X M3 DCT failed at 170k miles. It cost $14k to replace and install.

Best bet is to get a used low mileage DCT (<60-80k miles) through Deans Bimmer (///M Porium in Texas). They might service it for you first with new seals, filters, fluid...so it is a drop in. Important to synch the ECU and DCT software too to the latest BMW versions.

Depending on the state you live in, you might not find reliable BMW Techs or complex servicing of things like the DCT. Might need a road trip to a reputable shop hundreds of miles away that specialize in ///M cars.

The DCT pan (bottom), mechatronics units (side) and harness o-ring seal (top) are all different. The o-ring leak might not cause any shifting problems, unless you lost a liter or more of fluid.

If you drop the DCT...service the drive shaft rubber components to get rig of any clunks noises, including the Guibo, Center Bearing, and maybe the rear CV Joint.

Good luck...BMW DCTs are a black hole. BMW Dealerships won't open them up for repairs and rebuilds.


Cheers

Curious, how did your DCT fail?

[nyc_dude]

BMW Dealerships don't troubleshoot DCT internal problems. I asked them to get a BMW Field Engineer to look at the unit after the swap, but they ignored the request. Ironically, the fuel pump failed at the exact same time. $14k + $1k. So it could actually have been the fuel pump and not the DCT. Having the BMW Field Engineer check the DCT was to see if the fuel pump was at fault and not the DCT, so they can return my $14k.

What actually happened was, I was driving on the highway and the car shifted into N and engine RPM went to zero.

That was the last time I went to that dealership in SoCal that serviced my M3 for 9 years.

Never again in terms of buying a New BMW and getting service at a BMW dealership. We are spoiled with great BMW Indy Shops in SoCal.


Cheers