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.
The oil pan is moist.
The wiring harness gasket had maybe the biggest leak. It had dripped all the way down and murked the mechatronics cover.
Suction filter and suction pump were changed.
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.
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.
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.
At least unhooking the mechatronics allowed for more complete cleaning of the old transmission fluid behind it.
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.
Who doesn't upgrade the flywheel when transmission comes off? M4/S55 flywheel was fitted. Original still in the picture.
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.
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)
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.
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.
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.
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.
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...
Another DCT on the table.
The oil pan is moist.
The wiring harness gasket had maybe the biggest leak. It had dripped all the way down and murked the mechatronics cover.
Suction filter and suction pump were changed.
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.
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.
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.
At least unhooking the mechatronics allowed for more complete cleaning of the old transmission fluid behind it.
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.
Who doesn't upgrade the flywheel when transmission comes off? M4/S55 flywheel was fitted. Original still in the picture.
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.
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)
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.
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.
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.
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.
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...
