Piss oneself

Piss oneself

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

In this entry, the loaner DCT got on its worse behaviour and pissed itself nearly dry. We try fixing her up by fitting the prototype DCT Motorsport pan hoping it wasn't too late."
- Matt

From erratic to schizophrenic. 

No matter the error codes from the loaner DCT we fitted in the previous entry, I needed a car to haul me around for the next few weeks. I set the drivelogic to D1 as it uses the least fluid pressure to operate the clutches. 

On a 300km highway trip, I experienced major stalling issues. The transmission would trigger pressure and temperature codes with an orange COG. It would refuse to shift any gears, idling in neutral, even at highway speeds. 

I had to stop, and restart the car 4x times on this 300km trip. This was way, way worse than slipping clutches. Something was off. 


I got the car back to Phil's after a trip to the beach. I had noticed obvious signs of leakage having parked the car for extended period of time during the last 3 weeks. 

What we discovered would turn out to be the main cause of all issues related to the loaner DCT.

The transmission undertray was covered in fluids, inside and out. 

The original Genuine BMW plastic pan on this DCT was wet. It was one of the worst looking unit the guys had seen. 

Let's do an exercise in napkin mathematics. The standard DCT will hold around 9 liters / 2.4 gallons of fluid.The pan holds a little less, roughly 7 liters / 1.8 gallons. The M18 drain plug is roughly 0.7 inches in diameter.

The gravity flow rate for this diameter is very roughly 11 gallons per minute depending on fluid temperature. A standard flush should take roughly 10 seconds. 

We drained the pan under 3 seconds. 

In times of needs [...] prototype!

I've had the prototype billet DCT pan sitting on my shelf for close to 9 months. The project had been delayed due to focus on other CNC machining projects, amongst other things. 

I was awaiting updated pan bolts and a new drain plug to test for the DCT Motorsport pan

Genuine BMW bolts cannot be reused on this unit. 

A quick fit. 

The installation process for the pan is the same as described in the second Build Journal entry of this Special Series here. There are a few elements that need to be transferred from the original pan. 

This entire service shouldn't take more than 2 hours. 

The magnet needs to be transferred over. The original plastic screw does not fit here. A new bolt is provided along with a washer.

Do not over torque this as you risk breaking the magnet :) This DCT really wasn't in great shape. 

The original pick up on the loaner DCT had a slight crack. We opted not to fit the extender this time around. We would wait for the subsequent DCT and order a new pump just in case. 

The prototype drain plug was fitted and torque to spec. The production unit will have a larger thread to fit the original drain plugs and aftermarket magnetic types. 

The seal was created with high temperature silicone, aka "gasket maker". 

You have a short window to seal the pan to the transmission upon applying the silicone. Read the instructions on the tube!

AH! This being a prototype, we had little things to adjust on the fly. The supplied bolts were a had a few millimetres that needed to be shaved off. 

And BAM! We quickly bolted in the pan to secure the seal. 

Every bolt was torqued to specifications provided by BMW's technical bulletins.  

The GTS fill. 

I previously documented the GTS banjo bolt features, installation and the uprated filing procedures for the enlarged Motorsport pan here. I skip the filling details in the current entry. 

At the core of the GTS fill is the mysterious banjo bolt. It's a little trick that allows you to augment the pan's fill without having to tilt the car. 

We fitted the Banjo bolt to the fill plug by the passenger side of the transmission. One washer per side is required for a proper seal. 

I had previously used LiquiMoly's 8100 DCT fluid. This time around, we went with Motul's. I don't have a preference here, we just used what we had around. Motul does tend to blend great oils. 

We first filled to room temperature until it leaks from the GTS bolt, and then proceeded with the ISTA filling protocol.

The car was started up, RPMS were raised to 2,000 RPM until we reached the target fluid temperature. We filled it again until it leaked and that was it. 

The undertray was cleaned and put back on. It clears the lower hanging pan with ease. 

It worked. 

I had grew accustomed to some part of the DCT's degradation. Having stiffened the chassis, including the recent polyurethane differential bushings, I wrongly assumed the DCT's behaviour were normal. 

The new pan and proper fluid fill fixed everything. I was able to remember was a properly functioning DCT feels it. 

It's even better with GTS software, a lightweight flywheel, a carbon driveshaft and stiffer rear end bushings: it's telepathic. 


My DCT experiments aren't done yet. 

Up next: we're going back to the original transmission and we're going in for clutches. 

Until then, you can source the production version of the DCT Motorsport pan here

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