BMW 3-Series (E90 E92) Forum - View Single Post - Transfer Case "weakness"

amclint · 06-21-2012, 10:33 AM

Sorry for the book...

I hesitate to say I've been the most abusive to the TC, that honor may go to BobVader (Firepoule on youtube), but I'm surprised still that something hasn't broken. Having read all of Doyle's comments on the TC, I can see that there are weak areas but for whatever reason it almost seems like a lot of the TC failures have been more with stock cars. There is a veteran BMW tech on another local forum, I'm going to ask him what he sees on the 335/535xi with regards to the drivetrain. I've also talked to Level10 and a few shops doing TC work on the ATC700, the consensus is that power alone isn't what causes failures but rather stress and sudden engagements. Another reason Level10 told me to stay away from running slicks on my car without planning on replacing the axles and TC.

My notes:
-250 brake boost launches, many from 1st gear have all 4 spinning at hitting the rev limiter when I don't catch the 1st to 2nd shift quick enough.
-Very limited driving in Snow/Ice (bought the car after the harsh 2010/2011 winter, figures almost no snow this year!)
-A few (<5) hard launches at the drag strip where I had TOO much traction and got crazy wheel hop, as Carl said this is highly undesirable and I purposefully go out of the groove to get LOSE some traction.
-Currently on meth I'm doing nearly 460lb ft of torque to the wheels, I've added nitrous a few days ago and while I'm not spraying in 1st gear I am spraying in 2nd gear and I'm positive it's over 500lb ft of torque. My bottle is empty but I will be taking some logs and posting them up when I get it filled and things tweaked a bit more.

So far this mantra is serving me well, and I've stuck with it for nearly 8mo of hard driving:

1. Proper level of fluids in the trans/diffs/transmission is very important, trans especially as it can leak without being too obvious and the low fluid causes excess heat which leads to clutch pack wear.
2. Launch from 1st gear, even though it's slower overall in the 1/4, shift before the car wants to to keep from hitting the rev limiter (high powered cars, the rapid acceleration makes the car think the wheels are spinning and it suspends shift logic)
3. Launch in such a way that I lose traction for the initial run, this is helping keep the drivetrain happy. As the Level10 guru told me, traction + power = broken drivetrain
4. On nitrous at max power (over the trans torque limit, 500-550wtq range) it seems like you should actually NOT short shift because the DME preps the engine and trans for the shift at redline, vs having to react to a shift before redline. I'll know more as I continue to test this, but I'm hoping this combined with the JB4 shift damper/delay and cutting nitrous off 200-400rpm before the shift will alleviate drivetrain stress.

06-21-2012, 10:33 AM	#11
amclint boom 12 Rep 598 Posts Drives: 335xi Join Date: Apr 2011 Location: Varies iTrader: (6)	Sorry for the book... I hesitate to say I've been the most abusive to the TC, that honor may go to BobVader (Firepoule on youtube), but I'm surprised still that something hasn't broken. Having read all of Doyle's comments on the TC, I can see that there are weak areas but for whatever reason it almost seems like a lot of the TC failures have been more with stock cars. There is a veteran BMW tech on another local forum, I'm going to ask him what he sees on the 335/535xi with regards to the drivetrain. I've also talked to Level10 and a few shops doing TC work on the ATC700, the consensus is that power alone isn't what causes failures but rather stress and sudden engagements. Another reason Level10 told me to stay away from running slicks on my car without planning on replacing the axles and TC. My notes: -250 brake boost launches, many from 1st gear have all 4 spinning at hitting the rev limiter when I don't catch the 1st to 2nd shift quick enough. -Very limited driving in Snow/Ice (bought the car after the harsh 2010/2011 winter, figures almost no snow this year!) -A few (<5) hard launches at the drag strip where I had TOO much traction and got crazy wheel hop, as Carl said this is highly undesirable and I purposefully go out of the groove to get LOSE some traction. -Currently on meth I'm doing nearly 460lb ft of torque to the wheels, I've added nitrous a few days ago and while I'm not spraying in 1st gear I am spraying in 2nd gear and I'm positive it's over 500lb ft of torque. My bottle is empty but I will be taking some logs and posting them up when I get it filled and things tweaked a bit more. So far this mantra is serving me well, and I've stuck with it for nearly 8mo of hard driving: 1. Proper level of fluids in the trans/diffs/transmission is very important, trans especially as it can leak without being too obvious and the low fluid causes excess heat which leads to clutch pack wear. 2. Launch from 1st gear, even though it's slower overall in the 1/4, shift before the car wants to to keep from hitting the rev limiter (high powered cars, the rapid acceleration makes the car think the wheels are spinning and it suspends shift logic) 3. Launch in such a way that I lose traction for the initial run, this is helping keep the drivetrain happy. As the Level10 guru told me, traction + power = broken drivetrain 4. On nitrous at max power (over the trans torque limit, 500-550wtq range) it seems like you should actually NOT short shift because the DME preps the engine and trans for the shift at redline, vs having to react to a shift before redline. I'll know more as I continue to test this, but I'm hoping this combined with the JB4 shift damper/delay and cutting nitrous off 200-400rpm before the shift will alleviate drivetrain stress.
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