DCT maintenance to fix manual mode shifting problem

n54dct

Lurker
Sep 7, 2018
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Finland
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E92 335i, N54 & DKG
About 6 months ago, I noticed that the transmission oil pan was sweating a bit. I thought it was not an acute problem and thought that I would have the gasket changed later at the same time when doing some other maintenance. However, about 3 months ago, shifting problems started to occur with the manual mode. After a few shifts the gear would stick on and not go up or down from the paddles or the stick. Had to switch to N and from there back to D to get over it. This problem occurred with manual mode only, D and S modes worked perfectly and smoothly. No fault codes, no rough shifts, no clutch slipping. Sometimes the car would also directly start on M1 instead of D1. When this shifting problem started, instead of changing just the oil pan gasket it was decided to do the gearbox maintenance properly.

Another DCT on the table.
24847


The oil pan is moist.
24849


The wiring harness gasket had maybe the biggest leak. It had dripped all the way down and murked the mechatronics cover.
24848


Suction filter and suction pump were changed.
24850


Clutch cover o-ring and radial shaft seal were changed, no further work here was performed. The colored ring you can see seems to be motor oil. The engine oil pan also has a small leak near the flywheel which probably had picked up the motor oil and hurled it around and tattooed it inside the bell housing over time. The clutch cover and shaft itself were dry.
24852


Original pressure filter was replaced with SSP steel mesh filter. It has been common that steel mesh filters last longer but filtrate a bit worse than paper filters. However, this filter has pleats that the original does not, which can improve filtration.
24853


Mechatronics came off for cleaning too. The initial thought was to split the valve body in half to clean the canals and solenoids inside, but after it was on the table it was decided to not go forward with it as there was no certainty of the outcome.
24854


At least unhooking the mechatronics allowed for more complete cleaning of the old transmission fluid behind it.
24855


Original mechatronics cover was replaced with machined aluminum Slon Workshop cover. This cover uses sealant paste (Loctite 574) instead of a gasket. Output flange seal on the edge on the right was changed as well.
24856


Who doesn't upgrade the flywheel when transmission comes off? M4/S55 flywheel was fitted. Original still in the picture.
24857


The original oil pan was replaced with Wortec cast aluminum oil pan. Loctite 574 was used here too instead of a gasket. A small amount of oil was circulated through the oil cooler/heat exchanger lines to ensure the best possible oil purity. Dual-clutch gearboxes do not benefit as much from flushing as torque converters do as they contain no turbine wheel.
24858


The following service functions were carried out with ISTA/D:
-DKG: Oil balancing (ABL-DIT-S2360_GSOAG_M3)
-Twin-clutch gearbox: flushing function (ABL-DIT-S2360_GSSPUL_M3)
-Transmission control unit: parking lock hook test (ABL-DITS2360_GSHAK_M3)
-Gearbox adaptation (ABL-DIT-S2360_GSTEA_M3)
24859


It is unclear what the flushing function/purging function actually does, as it seems to be only an internal stand-alone function without the need to connect a flushing apparatus to the transmission. It can be performed without opening a single screw on the car.
24861


After the oil balancing function, an additional liter of oil was filled with a "customized M3 GTS filling method" of raising the passenger side in the air. Officially in the M3 GTS an oil filler neck is used in place of the fill plug to gain the additional oil volume. I can confirm that this trick indeed eliminates the initial lag when moving from standstill. In total, approximately 9-10 liters of Motul DCTF went into the completely drained transmission.
24862


As for the manual mode shifting problem... after this extensive maintenance, it was NOT fixed. At this point the problem seemed purely electrical so I remembered that I had previously changed my SSG style paddles to Nelson Racing Wheel paddles. I wanted to keep my original paddles intact and requested the new paddles to be assembled to a new pair of paddle bases. The quality of the paddles was perfect and they worked fine. However, the manual mode shifting problem started disturbingly close to the switching of the paddles. Of course I first thought that the problem was caused because the mechatronic valve body was starving from oil because of the leaks. After all, the paddles worked perfectly and even allowed to shift from one to ten times before the gear got stuck.
24863


According to RealOEM, there are paddles for the E9x series with 7 different part numbers and some are not interchangeable. Decided to try moving the new paddles to the old paddle bases to see if there was any change. When closely inspecting the base sections of the old and new paddles, it was noticed that the electrical circuit boards had different numbers. The manual mode shifting problem had been solved.
24864


It is still a mystery why the paddles caused so peculiar problems. Why did they also affect shifting from the stick? Why they sometimes allowed to shift ten times before getting stuck and sometimes only one time? Why did the car sometimes start on M1 instead of D1, but only sometimes and not always? These questions might remain unanswered. This maintenance nevertheless had to be done because of the leaks and it also gave the excuse to upgrade some parts as the transmission was coming off anyway. It is always mentally easier to cope with the monetary costs if it is an upgrade rather than a repair...
 

aus335iguy

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Nov 18, 2017
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335i DCT 2009
I had no idea that slonik made a mech cover as well. I believe that the flush function is used to run all of the oil out of the lines and into the pan prior to doing a refill.(i think i read that somewhere)
 

pe7er

Lurker
Jul 26, 2018
15
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335i
nice job ! where did you get the m3 gts draining valve?
i dont know anymore where i read that, but it is important to fill the correct amount of dct fluid into the gearbox, also not more than mandatory. is that nonesense?
 

n54dct

Lurker
Sep 7, 2018
16
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Finland
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E92 335i, N54 & DKG
nice job ! where did you get the m3 gts draining valve?
i dont know anymore where i read that, but it is important to fill the correct amount of dct fluid into the gearbox, also not more than mandatory. is that nonesense?

The M3 GTS oil filler neck is not needed if the transmission is filled while the car is in a tilted postition; the tilting allows the transmission to be filled to the same capacity as with the oil filler neck (without tilting).

No harm can come from filling with this method. The M3 GTS has the exact same transmission with the same oil pan, only fluid capacity is different. If anything, the additional fluid should aid in cooling and lubrication thus increasing the lifespan of the transmission.
 

n54dct

Lurker
Sep 7, 2018
16
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Finland
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E92 335i, N54 & DKG
What does the M4 flywheel feel like?

The low rev range feels much lighter and smoother and the engine responds much quicker down low. This feels the most when accelerating from standstill and low speeds. Cannot really say anything about benefits in higher speeds but the car is definitely faster off the line. In my opinion, also the character of the engine feels better in daily driving because of the increased responsiveness.

On D mode without sport button the flywheel also seems to allow the revs to go lower than with the stock flywheel before downshifting. This might negatively affect daily driving of single turbo users as they don’t generally have much low end torque. With sport button on the revs are always in the power range though.

Relatively quiet flywheel chatter can be heard when idling if you are sensitive to noise changes of your car. The noise can be covered by raising the idle with MHD but I find that unnecessary as the tone is pleasant and noise level almost nonexistent.
 
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n54dct

Lurker
Sep 7, 2018
16
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Finland
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E92 335i, N54 & DKG
What is it with these paddles? :laughing: How can they cause this kind of problems... According to the electrical symbols on the wiring diagram the paddles are just regular switches.

25131
 

n54dct

Lurker
Sep 7, 2018
16
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Finland
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E92 335i, N54 & DKG
I believe @LMB335is started having issues with the addition of a different SZL.

I see. My problems still remain a mystery if the paddles are just regular switches. Im just glad that in the end the fix was so simple and easy and there was no bigger fault with the transmission itself.

I don't have the guts to do the M3 GWS/flash conversion. I asked xHP sometime ago if they are developing anything for the BMW DCT. They gave a cryptic answer "not right now but that might change in the future". Maybe all DCT owners should bomb them with emails and pressure them into developing something for us too? :grinning:
 

n54dct

Lurker
Sep 7, 2018
16
9
0
Finland
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E92 335i, N54 & DKG
It’s pretty clear that XHP can’t do DCT. If they could they would’ve done it by now. :tonguewink:

No no I think they just haven't invested the time and effort into the DCT because it's market share is so low compared to the ZF gearboxes. Never lose faith :D