"These build journal entries are part of a Special Series on the DCT major service, updated GTS filling specifications and upgraded, oversized, DCT pans. 

This journal entry documents the various failure points of the DCT transmission in the E9x M3."
- Matt 

The DCT is awesome...

The DCT transmission is a marvel of engineering and remains to this day the best automated transmission BMW M ever fitted to a car. 

G8X guys, my bad - ZF 8 speeds aren't all that, and SMG3 owners need to take a pause and be rational about what we got with the S54 and S85. 

The DCT transmission are notoriously known for being designed as Lifetime Fluid by BMW M. That may very well be accurate for street use and under normal use. 

..but BMW didn't plan for this. 

Unfortunately for us, BMW didn't expect its DCT transmissions to leak as we now know today. This is further reflected in BMW's own notes on its Technical Service Bulletin on the DCT.

They specifically mention to be very selective in DCT fluid maintenance as the Genuine BMW Pentosin DCTF-1 (83220440214) fluid supply and availability is scarce, and extremely expensive at close to 40$ per liters. 

The entire DCT system is filled with up to 7.8 liters of it, some say it's 9 liters. It isn't clear. 

Fortunately for us, we have permanent fixes to most of the DCT leaking issues and access to much more affordable DCT compatible fluids. 

I sort of planned for this...

Back in November 2021, I started noticing my E92 M3 DCT transmission was leaking from all over the place. 

I was planning the TTV Racing S65 DCT Lightweight Flywheel and decided to combine with a complete DCT transmission service. It still came out to be an expensive while you're in there maintenance. 

I say sort of as I was initially expected only the main pans to be a leaking problem. I had a MDCT Motorsport Main Oil Pan and Side Pan ready to go. 

...but not like this:  

It was leaking from everywhere: top, side & bottom.

The Mechatronic O-Ring

The main oil pan is often the easy target to point fingers at for leaking DCTs and it is where oil will obviously accumulate. 

My experience was different. The Mechatronic O-Ring was worn and obviously leaking all over the transmission. 

You can see the accumulation of oil and dirt at the top of the transmission. 

 

The Side Pan

The OEM side pan is made from aluminum, and has less tendencies to leak versus the OEM plastic main oil pan which tends to warp and leak. 

Yet it still can, and it should be planned for when pulling the transmission. 

The OEM aluminum side pan still use a rubber gasket which tends to dry out over time. The side pans covers the electronics of the DCT which bath in transmission fluid. 

The Main Pan

The obvious culprit was also leaking on my transmission. This is another case of BMW using plastic where it should have used another material. 

The S65 and S85 and both riddled with such cost cutting measures: throttle actuators, VANOS covers, coolant bleeder screw, power steering fluid covers, etc. 

It's still just a BMW, even if it has an M badge. 

 

The revised plan. 

As we clean and analyzed the leaks to better understand where they originated, we decided to go all in and perform a total service. 

Upgrades:

1. CNC'ed aluminum oversized main pan without gaskets
2. GTS banjo bolt
3. CNC'ed aluminum side pan without gaskets.  

Maintenance:

1. Genuine BMW Suction Cartridge Filter (SKU: 28107842828)
2. Genuine BMW Side Filter (SKU: 28107842840)
3. Mechatronic O-Ring (SKU: 28607849555)
4. New Coolant Hose (SKU: 17222283594)
5. New Coolant Hose O-Rings (2x) (SKU:17222245358)
6. 9x liters of LiquiMoly 8100 Series DCT fluid

We had to change the coolant hose as it was appeared to be slightly leaking and we didn't want to take any chances.  

Up next: I document the installation process and detail the GTS filling specifications.