[amclint]

Originally Posted by jpsimon

where are all these XI people with blown transfer cases? i've had not a single issue with my car. Are they all living their life a quarter mile at a time or what?

Been a handful of threads about the XI drivetrain, some input on a few failed ones and other input from dealership employees (nobody knows if failures are from tunes or not). Because there are so many fewer XIs running around than Is, and even less that are tuned AND even less pushing over 450tq we just don't have the data to make any solid conclusions. What I'm personally going on is that BMW didn't trust the unit for it's cars running over 400tq, and didn't trust it even on their small SUVs that weigh a good bit more. The ATC300 in the 335xi is a small transfer case, and is a viscous clutch setup instead of straigth gears. Also it has a weak worm drive gear in there and as far as I know no cooling setup for the fluid.

As I see it, very few options at this point:
- Leave it stock, see how much power/type of usage eventually breaks it
- Pull apart stock unit, try to strengthen individual components (Doyle's idea)
- Try to fit ATC350 and work out any electronics issues (unlikely)
- Try to fit an aftermarket cooler somehow to keep temps down, not sure how much temps affect the viscous clutch setup so this may be moot.
- Buy a different car that doesn't have this 'perceived' issue

Truth is one of us XIs needs to take the jump and put RBs or a single turbo on and see what happens

[Todd135i]

Most transfer cases I've seen get destroyed (EVO's), came from dumping the clutch. I've seen the stress from the shock or wheel hop or both combined, destroy the transfer case. The proper way was to slip the clutch. Dumping the clutch was the worse thing you could do.

I know they're completely different cars but I'd think this would also apply here.
I'm new to BMW's so correct me if I'm wrong.

[themyst]

Originally Posted by DefactoM6

Yup, I've heard of one owner (first hand) who blew a transfer case after some serious abuse, but he also blew out a stock clutch in 10k miles with just a JB3, TBE and intakes. He now has a M3 DCT with a VT625 setup...much harder for him to break. :P

As for all the naysayers talking about transfer cases, I think back to the days of when people thought that the limits of a stock bottom end 2JZ was 450whp. There's no way of knowing what kind of power it will handle until someone tries it. And frankly, I believe that if someone doesn't deliver flagrant, ridiculous abuse upon it, and maintains it, that situations like the above won't happen until silly power levels are hit, or until that comes in tandem with some abusive launching. As for the AT however, I think we already know where it's TQ capacity lies.

We're both talking about Rick. but yes he is extremely hard on his cars.

[DefactoM6]

Originally Posted by themyst

We're both talking about Rick. but yes he is extremely hard on his cars.

LOL, small world. Funny thing is, he thinks that I'm a crazy driver...yet I've never had those kinda things happen to me... I drive hard, but I treat her nicely .

[rooringhusky]

Originally Posted by enrita

For single turbo i would go MT only, just my 2c.

This

[SaviorXi]

I would think the 5k launches with the manual tranny would be the worst for the transfer case. For all the talk and speculation I have seen very little proof. I have been running my auto AWD hard as hell with hundreds of launches on Cobb stage 2+ and I have felt nothing wrong in over 20,000 hard miles. That is not to say that tommorow could not be the day shit goes to hell for me on my spirited drive home from the office. We all know that the risks increase as the HP and torque do. I just want to see more evidence before I make any final assumptions about the strength and longevity of the transfer case and auto tranny. I am sure we wll find out soon enough.

[amclint]

Originally Posted by SaviorXi

I would think the 5k launches with the manual tranny would be the worst for the transfer case. For all the talk and speculation I have seen very little proof. I have been running my auto AWD hard as hell with hundreds of launches on Cobb stage 2+ and I have felt nothing wrong in over 20,000 hard miles. That is not to say that tommorow could not be the day shit goes to hell for me on my spirited drive home from the office. We all know that the risks increase as the HP and torque do. I just want to see more evidence before I make any final assumptions about the strength and longevity of the transfer case and auto tranny. I am sure we wll find out soon enough.

Interesting conversation I had with the main guru at Level 10 focused on what actually causes the transmission/transfer case/diff/axles to fail on a car. From our conversation it's his opinion that most of the failed parts he sees are a direct result of a violent stress event not sustained power over the long term. IE, a hard launch with lots of traction vs just having a ton of power in general.

His recommendation to me was to stay away from really sticky tires without upgraded drivetrain components, and only start in 1st gear. Also said don't shy away from the water box as some spin at launch is better than a hard hook, especially where our transfer case design isn't great at handling sudden power inputs (clutch vs gear).

My advice to any guys drag racing the XI on the stock drivetrain:
-Only use 1st gear
-Try not to brake boost more than 1 to 1.5 seconds before launch
-Try not to brake boost so high your meth starts flowing it just feels brutal on the car
-Shift yourself on the 1st to 2nd gear change as the needle starts to pass 5k
-Don't run drag radials without knowing the risks
-Top off the AT fluid
-Change your AT/Diff/Transfer Case fluids more frequently (every 50k/2yr is recommended without mods, so maybe every 20-25k?)

[enrita]

Originally Posted by mykal335xi

Interesting conversation I had with the main guru at Level 10 focused on what actually causes the transmission/transfer case/diff/axles to fail on a car. From our conversation it's his opinion that most of the failed parts he sees are a direct result of a violent stress event not sustained power over the long term. IE, a hard launch with lots of traction vs just having a ton of power in general.

His recommendation to me was to stay away from really sticky tires without upgraded drivetrain components, and only start in 1st gear. Also said don't shy away from the water box as some spin at launch is better than a hard hook, especially where our transfer case design isn't great at handling sudden power inputs (clutch vs gear).

My advice to any guys drag racing the XI on the stock drivetrain:
-Only use 1st gear
-Try not to brake boost more than 1 to 1.5 seconds before launch
-Try not to brake boost so high your meth starts flowing it just feels brutal on the car
-Shift yourself on the 1st to 2nd gear change as the needle starts to pass 5k
-Don't run drag radials without knowing the risks
-Top off the AT fluid
-Change your AT/Diff/Transfer Case fluids more frequently (every 50k/2yr is recommended)

i launched my car from a dig maybe 3-4 times since i purchased it in 2008. I must say though that my AT started failing right after i fitted car with the yoko neova tyres.

[Doyle]

Originally Posted by mykal335xi

Interesting conversation I had with the main guru at Level 10 focused on what actually causes the transmission/transfer case/diff/axles to fail on a car. From our conversation it's his opinion that most of the failed parts he sees are a direct result of a violent stress event not sustained power over the long term. IE, a hard launch with lots of traction vs just having a ton of power in general.

His recommendation to me was to stay away from really sticky tires without upgraded drivetrain components, and only start in 1st gear. Also said don't shy away from the water box as some spin at launch is better than a hard hook, especially where our transfer case design isn't great at handling sudden power inputs (clutch vs gear).

My advice to any guys drag racing the XI on the stock drivetrain:
-Only use 1st gear
-Try not to brake boost more than 1 to 1.5 seconds before launch
-Try not to brake boost so high your meth starts flowing it just feels brutal on the car
-Shift yourself on the 1st to 2nd gear change as the needle starts to pass 5k
-Don't run drag radials without knowing the risks
-Top off the AT fluid
-Change your AT/Diff/Transfer Case fluids more frequently (every 50k/2yr is recommended without mods, so maybe every 20-25k?)

Highlighted the important!

As most have mentioned, outside of a few users, the TC has been surprisingly robust. There are quite a few members that are likely putting out 450+ wtq. 450+ wtq is no big deal for most FBO guys, now. However, I have yet to really hear about people using slicks and getting sub 1.5 60's. That is when things will get interesting.

The only way to know is with destructive testing.

Also, change you diff fluids if you're over 50k. I know it was said above, but it bears repeating!

[JamesM3M5]

The power flow through the ATC300 is directed 100% to the rear wheels until the clutches are tightened by the servomotor. It's not viscous, but a mechanically controlled set of clutches with variable grip from a cam wheel and adjusting levers that can put more or less pressure on the clutches. The cam wheel is run by a servo motor, and the cam pushes on the adjusting levers to give more or less torque transfer to the front tires. The clutch pack can sustain full lockup allowing 100% torque to the front wheels if the rears have no traction (such as on ice or snow).

I would venture that running stickier tires on the REAR ONLY will help reduce front driveline and transfer case damage for drag racing. This is probably the only case where the transfer case and front diff/driveshaft are the most vulnerable to torque-induced failure.

[amclint]

Originally Posted by JamesM3M5

The power flow through the ATC300 is directed 100% to the rear wheels until the clutches are tightened by the servomotor. It's not viscous, but a mechanically controlled set of clutches with variable grip from a cam wheel and adjusting levers that can put more or less pressure on the clutches. The cam wheel is run by a servo motor, and the cam pushes on the adjusting levers to give more or less torque transfer to the front tires. The clutch pack can sustain full lockup allowing 100% torque to the front wheels if the rears have no traction (such as on ice or snow).

I would venture that running stickier tires on the REAR ONLY will help reduce front driveline and transfer case damage for drag racing. This is probably the only case where the transfer case and front diff/driveshaft are the most vulnerable to torque-induced failure.

This is contrary to what I've read on at least the 2008xi, which is that with the driveshaft going straight through to the rear wheels the most torque that the front can ever get would be 50%.

There is one guy that runs DR on the rear, would be nice if we could log somehow when the power goes to the front to see if it helps.
http://www.e90post.com/forums/showpo...0&postcount=82

Of course, then you have the issue of DR on the car at all, which will equate to trans and rear half-shaft issues, but at least it takes the strain off the TC and front diff if that idea worked!

[amclint]

Originally Posted by JamesM3M5

The cam wheel is run by a servo motor, and the cam pushes on the adjusting levers to give more or less torque transfer to the front tires.

I was reading a long thread about the worm gear (steel) which is turned by a plastic gear, that is attached to a servo motor. Would it make sense that the more power the car has, the harder this plastic gear/servo motor has to work to get the clutch packs to engage and transfer torque forward?

I just wonder when I see my transfer case fail, if this isn't going to be the weak component. If so, am I crazy for thinking I could just have a CNC machine cut out a gear the exact same size as the plastic one for some added strength?

[Bleep]

Originally Posted by mykal335xi

Interesting conversation I had with the main guru at Level 10 focused on what actually causes the transmission/transfer case/diff/axles to fail on a car. From our conversation it's his opinion that most of the failed parts he sees are a direct result of a violent stress event not sustained power over the long term. IE, a hard launch with lots of traction vs just having a ton of power in general.

His recommendation to me was to stay away from really sticky tires without upgraded drivetrain components, and only start in 1st gear. Also said don't shy away from the water box as some spin at launch is better than a hard hook, especially where our transfer case design isn't great at handling sudden power inputs (clutch vs gear).

My advice to any guys drag racing the XI on the stock drivetrain:
-Only use 1st gear
-Try not to brake boost more than 1 to 1.5 seconds before launch
-Try not to brake boost so high your meth starts flowing it just feels brutal on the car
-Shift yourself on the 1st to 2nd gear change as the needle starts to pass 5k
-Don't run drag radials without knowing the risks
-Top off the AT fluid
-Change your AT/Diff/Transfer Case fluids more frequently (every 50k/2yr is recommended without mods, so maybe every 20-25k?)

Of course, what breaks drivetrains is not power but having enough traction to put all that power down.

I'm confused about only starting in 1st gear though, wouldn't that put the max amount of torque down and thus put the most stress on the drivetrain components?

[JamesM3M5]

Originally Posted by mykal335xi

This is contrary to what I've read on at least the 2008xi, which is that with the driveshaft going straight through to the rear wheels the most torque that the front can ever get would be 50%.

There is one guy that runs DR on the rear, would be nice if we could log somehow when the power goes to the front to see if it helps.
http://www.e90post.com/forums/showpo...0&postcount=82

Of course, then you have the issue of DR on the car at all, which will equate to trans and rear half-shaft issues, but at least it takes the strain off the TC and front diff if that idea worked!

Yeah, technically yes the front wheels will see 50% and the rear 50%, but the way BMW worded it in the training literature was that if the rears had NO traction, the fronts can sustain up to 100% of the driving torque. This, of course, only pertains to icy/snowy conditions, not dry pavement.

[JamesM3M5]

Originally Posted by mykal335xi

I was reading a long thread about the worm gear (steel) which is turned by a plastic gear, that is attached to a servo motor. Would it make sense that the more power the car has, the harder this plastic gear/servo motor has to work to get the clutch packs to engage and transfer torque forward?

I just wonder when I see my transfer case fail, if this isn't going to be the weak component. If so, am I crazy for thinking I could just have a CNC machine cut out a gear the exact same size as the plastic one for some added strength?

I dunno. That servo gear is always doing something on the stock setup, especially working hard once conditions get slippery. It's possible to get a performance transmission shop to make a steel gear or even maybe contact odometergears.com (Jeff, I think?) to get new gears made as needed. I don't think it sees a lot of load, just a lot of movement, to move the cam that pushes on the clutch pack adjuster arms.

[amclint]

Originally Posted by Bleep

Of course, what breaks drivetrains is not power but having enough traction to put all that power down.

I'm confused about only starting in 1st gear though, wouldn't that put the max amount of torque down and thus put the most stress on the drivetrain components?

In the XI 2nd gear starts are the fastest because we have the torque to pull through and you don't lose time on the 1st to 2nd shift, but they toast the auto trans parts for that specific gear. From a torque perspective, 2nd gear would have more torque too as at least in my case I could hold ~3.5k rpm on the converter with brake boost in 2nd, and just barely 2500 rpm in 1st. With 2nd gear boost I was at almost 10psi and meth was flowing when I would finally release the beast !

Either way, at the end of the run ET wise it's only .1 to .15 faster, so not really worth killing the stock AT for. If you want to run an upgraded trans, then I would say go for it.

[amclint]

Originally Posted by JamesM3M5

I dunno. That servo gear is always doing something on the stock setup, especially working hard once conditions get slippery. It's possible to get a performance transmission shop to make a steel gear or even maybe contact odometergears.com (Jeff, I think?) to get new gears made as needed. I don't think it sees a lot of load, just a lot of movement, to move the cam that pushes on the clutch pack adjuster arms.

Good to know if it ends up being that part that fails, I didn't think about it being a wear issue, but that makes sense since the more power I make the more the rears slip and the servo has to move power forward.

[akotten]

For the record, I had a transfer case failure. However, I had just purchased the car w/ 51k miles and maybe had a tune for a week. I got the christmas tree lights of failure after just randomly driving over railroad tracks. I hardly even drove the car very hard. Ever since I replaced it though, I've driven it WAY harder, through autocross, HPDE, etc. What I want to know is what BMW changed when they went to "x-drive". The part numbers are different, but that's the t-case you get if you need a replacement now. I don't know which version I have on my car right now, because mine was replaced through my extended warranty, but I do know that the replacement supposedly had 11k miles on it.

[Doyle]

Originally Posted by JamesM3M5

I dunno. That servo gear is always doing something on the stock setup, especially working hard once conditions get slippery. It's possible to get a performance transmission shop to make a steel gear or even maybe contact odometergears.com (Jeff, I think?) to get new gears made as needed. I don't think it sees a lot of load, just a lot of movement, to move the cam that pushes on the clutch pack adjuster arms.

I would think that rapid torque "diversions" would cause slip between the cog and the worm gear. Almost like when using a drill to install a screw...too fast and you strip out the head. So when you launch at the strip, the worm gear goes from 0% engagement to 100% engagement very quickly.

Thats why I think heat and that worm gear are going to be the initial failure points.

[Bleep]

Originally Posted by mykal335xi

In the XI 2nd gear starts are the fastest because we have the torque to pull through and you don't lose time on the 1st to 2nd shift, but they toast the auto trans parts for that specific gear. From a torque perspective, 2nd gear would have more torque too as at least in my case I could hold ~3.5k rpm on the converter with brake boost in 2nd, and just barely 2500 rpm in 1st. With 2nd gear boost I was at almost 10psi and meth was flowing when I would finally release the beast !

Either way, at the end of the run ET wise it's only .1 to .15 faster, so not really worth killing the stock AT for. If you want to run an upgraded trans, then I would say go for it.

Yeah but I'd surmise that the torque multiplication in 1st gear would outweigh any benefits you'd get by launching in 2nd gear, even at higher RPMs. Especially considering the low end torque we've got. Peak torque on these cars are around 2-2.5k RPM anyway. In 1st gear at 2500 RPM on a Stage 1 Cobb tune an XI puts down 1125 lb-ft vs 615 lb-ft @ 3500 RPM in 2nd gear. Shift time could make sense but I doubt the 150ms will beat out double the torque in 1st gear. A hard launch on a FBO XI must have crazy low 60' times.

[amclint]

Originally Posted by Bleep

Yeah but I'd surmise that the torque multiplication in 1st gear would outweigh any benefits you'd get by launching in 2nd gear, even at higher RPMs. Especially considering the low end torque we've got. Peak torque on these cars are around 2-2.5k RPM anyway. In 1st gear at 2500 RPM on a Stage 1 Cobb tune an XI puts down 1125 lb-ft vs 615 lb-ft @ 3500 RPM in 2nd gear. Shift time could make sense but I doubt the 150ms will beat out double the torque in 1st gear. A hard launch on a FBO XI must have crazy low 60' times.

2nd gear is faster in the 1/8 and 1/4 mile but slower in the 60' and to 60mph. 1st gear is faster initially, but the shift strips the gain out and then some.

At least with my car, over the coarse of 250 launches, about 40% of which were 2nd gear, that is the case. As I've mentioned before, the hard launch in my XI and others suspends the regular shift logic (I hit rev limiter even without wheelspin on a hard 1st gear launch) so that may be why it shifts so slow, due to me having to do the shift manually.

Hardest 1st gear launch I ever did was at the drag strip, and it spun like crazy then hit the rev limiter, was a low 1.6x if I remember right. On better rubber and with good track prep/temps I have no doubt 1.5x is possible.

[335iPSI]

I've logged quite a few LOW 1.7's on the street --- these XI's HOOK UP! With the meth kit, procede and stiffer suspension, it really hauls. These T-cases seem to be very stout.