[Ilia@IND]

While the S65 engine of the E9x M3 has been the subject of fairly extensive study by many tuners and BMW enthusiasts since the car’s development, we feel that the knowledge base for the car’s incredible DCT transmission has remained quite limited, especially when compared to the wealth of information available about the car’s many drivetrain, suspension, and control systems.

With this in mind, we began to take a closer look at the DCT to understand what limitations the transmission had, and where those limitations would stop us and our fellow enthusiasts in enjoying our M3s. Over time it became abundantly clear that the transmission hardware was overall incredibly robust. Even after installing multitudes of ESS VT2 supercharger kits on our client’s cars and seeing those same cars log hundreds of track miles for several years, we’ve seen no hardware failures to date.

Clearly, then, the physical hardware seems to be robust enough for the most demanding M3 driver in even very stressful situations. From what we’ve seen, if the M-DCT transmission has any one weak point, it is temperature control. Damage to the clutches and other internal components can occur if the transmission temperatures climb above a safe level. Fortunately for all of us BMW M has protected us by forcing the M3 to enter a safe mode when the transmission temperatures rise above acceptable levels.

It is possible to achieve high enough operating temperatures to engage limp mode if operating in very high ambient temperatures while simultaneously making very high power levels. Although we’ve heard of very few instances where this has occurred, two of our clients with very high output engine setups operating in extremely harsh have encountered BMW’s DCT safe mode. Although both have only seen limp mode a couple of times, this prompted us to investigate further. Oddly, even basic information regarding the transmission’s operating temperature ranges was largely unknown by the BMW enthusiast community. After repeated queries, even our best contacts at BMW were not able to say exactly where the M3 chooses to enter safe mode to protect the DCT transmission, or what criteria are used to calculate this critical temperature!

I wanted to share the information we do know with the M3Post community, in hopes of expanding the community’s knowledge of the M-DCT transmission.

The DCT transmission uses two coolers to control temperature: a coolant to oil heat exchanger and a oil to air heat exchanger.



The coolant to oil heat exchanger facilitates a faster transmission warm up by circulating transmission oil through a bypass valve in the transmission thermostat (the thermostat is part number 9 in the above diagram). The transmission oil exits the thermostat and travels to the top of the transmission via a soft line (part number 12 in the above diagram) where it enters a heat exchanger. This heat exchanger uses warm coolant from the engine to help the transmission oil get to operating temperature more quickly during a cold start. The oil then returns to the thermostat block through pipe number 13 in our diagram, and re-enters the transmission. The coolant is circulated to the heat exchanger via an auxiliary coolant pump which is electronically controlled via the M-DCT computer and can be turned on or off when needed. This system will first bring the transmission oil up to operating temperature more quickly for better cold starts, and then use the engine cooling to maintain a stable transmission oil temperature once operating temperature has been reached.



At 203 degrees Fahrenheit, the thermostat opens oil flow to the front mounted oil to air cooler, positioned in the passenger side bumper opening. This oil to air cooler will work to maintain a stable oil temperature from that point forward. Part number 1 in the diagram above is the supply line to the oil cooler, and part number 2 returns the cooled oil to the transmission.

This covers the transmission cooling system during normal operation, but what about when the oil temperature exceeds BMW’s acceptable parameters? This is what we set out to explore. To help our clients better understand how their DCT transmission is operating, we created an adapter that can interface with a temperature sending unit to give an accurate reading of the DCT oil temperature.



We are still waiting for our friends at BMW to give us the maximum allowed temperature value, but in the mean time we will communicate with our clients who have already installed our DCT oil temp adapter and gauge set to monitor their experiences as they use their cars both on the street and the track.

I apologize for the long post, but I do hope that we can begin an open discussion about the DCT trans and educate the BMW community!

[NETO]

interesting read, looking forward to the answers from the members with knowledge/experience.

[SteDevote]

OP, thanks for the information. About all I have to add is that using launch control repeatedly, according to the manual, will result in overheating.

In the past, I have been a committed six-speed manual driver. The DCT is amazing and I honestly have not missed my manual transmissions of the past.

[Cleveland]

Ilia,

I'll add a few technical details to your DCT transmission knowledge base:


1) The BMW 7-speed DCT transmission (GS7D36SG) is built by Getrag using two Borg-Warner sourced wet clutch packs. 1st, 3rd, 5th, 7th, & Reverse can be engaged on one clutch, while 2nd, 4th, & 6th gear can be engaged on a second clutch. Either wet-clutch pack can be pre-engaged 8ms (milliseconds) before the shift happens.

2) The DCT's internal gear ratios are as follows:

1st: 4.780
2nd: 2.933
3rd: 2.153
4th: 1.678
5th: 1.390
6th: 1.203
7th: 1.000
Reverse: 4.454

2) The DCT transmission housing holds ~8-liters of a specially blended 75 weight transimission fluid manufactured by Pentosin in Germany.

3) The total capacity of the entire DCT system, which includes the transmission housing, the high pressure lines, the pump, and the DCT oil cooler, is ~9.5 liters.

4)The Pentosin DCT transmission fluid is called: BMW-DCTF-1

5) BMW part numbers for the Pentosin BMW-DCTF-1 fluid are as follows:

BMW 83 22 2 148 578 : DCTF-1 1-Liter bottle
BMW 83 22 0 440 214 : DCTF-1 1-Liter bottle

BMW 83 22 2 148 579: DCTF-1 20-Liter jug
BMW 83 22 2 147 477: DCTF-1 20-Liter jug

6) This Dual Clutch Tramsission fluid is also sold to the outside world, as Pentosin FFL-4.

*The product data sheet for this specially formulated Pentosin DCT fluid is listed in two attachments below.
















Comments from a Pentosin Chemical Engineer about the effects of intense heat on the BMW-DCTF-1 (FFL-4) fluid:

"We vex the FFL-4 for 192 hours at 170°C (338°F) by bringing in air. It is still okay after this treatment. But this is an aerobic treatment whereas in the gear box the FFL-4 sees an unaerobic atmosphere most of the time. If you take an hour of this lab test and estimate that, it is equivalent with an hour of the car running at 200 km/h (124 mph) you get a milage of 38400 km (23861 miles). But obviously one hour at 170°C under air stands for more than 1 hour at 200 km/h. According to BMW it is 5 hours at 200 km/h."

[Cleveland]

For anyone who is curiuos to see how the DCT transmission actually works...

http://www.youtube.com/watch?v=YmaAx...mbedded#at=137

http://www.youtube.com/watch?v=3JtTT...layer_embedded

http://www.youtube.com/watch?v=0mofq...embedded#at=19

[leo95se]

great thread..

[Oldman MZ3]

So far, out of all the cars we sold with DCT, not one failure.

[hamam3]

good thread subscribed

[chrisfast]

Question: If the car is in Manual and you take it to redline, will it automatically shift to the next gear, or will it hit the rev limiter? I am hoping that it will just hit the rev limiter. Thanks!

[Commissar Megre]

transmission does not switch