[pits200]

Originally Posted by David1

I have seen 2 shatered transfer cases in 6 months.

Are you saying that is a lot or a little? Just curious.

[Presidio335xi]

Originally Posted by Beemw335

Wow, the people on this forum truly surprise me.
My friend is on his 3rd transfer case, xi fbo with meth..
Its not anything new, most xi owners k ow that its the weak point on their cars.

Well that's a big sample size.

I'm FBO + Meth for 10k miles and no problem. Granted I am not at the 1/4 mile strip every wknd.

I wager that driving ability is the key factor and maybe the AT vs. MT. No brake boosting for us MT guys.

[nailer335]

Im embarrassed to say that at 67k miles, I havent even replaced the original transmission fluid

I went JB3 + DCI at 25k miles and then just very recently (3 months ago) upped things to JB4 15ohm, Mr5 intake and the 3 nozzle pre/post turbo meth, then DPs last week. Since then, I havent even gone through two full tanks of meth (1.5 gal tank in trunk) yet because I want it to be in prime condition before pushing it hard. Doyle posted a good thread for maintenance ideas before pushing really high boost so I'm going to dealership it with some specific instructions, including overfilling the transmission fluid by 1/2 to 1 quart with Pentosin ATF1, transfer case fluid, and motul differential fluid. At that time, I'll also have to put on new rotors/pads (stoptech ftw...) and might just bite on H&R coilovers too. I'm out of warranty and my mods are permanent and obvious so I wont be shy at this point lol I still roll no cowl.

[amclint]

Originally Posted by nailer335

Im embarrassed to say that at 67k miles, I havent even replaced the original transmission fluid

I doubt it needs much service, but since BMW in their infinite wisdom didn't give us a trans temp or fluid level gauge the general wisdom is to run as much fluid as possible to add just that little bit of extra cooling and lubrication under hard acceleration.

The actual instruction is to overfill via the fill hole and plug it as quickly as possible to keep as much in there as you can, no idea how much extra fluid that ends up being but I was just going to buy a quart and a pump and see how much it took.

One more interesting thing I found is that the 550ix's ATC350 is used in the Alpina B7X, and from everything I can find it is the stock unit with no physical upgrades. The Alpina B7 runs 500hp/517tq and weighs 4500lbs, obviously Alpina is very well known and respected as well as warrantied so this is a good sign for the ATC350!

Additionally if we are stuck with the ATC300, I've found a few shops that rebuild them with stronger chains, bearings, pads, etc so if I go further down that road I'll get a quote on an upgrade.

[nailer335]

Originally Posted by amclint

I doubt it needs much service, but since BMW in their infinite wisdom didn't give us a trans temp or fluid level gauge the general wisdom is to run as much fluid as possible to add just that little bit of extra cooling and lubrication under hard acceleration.

The actual instruction is to overfill via the fill hole and plug it as quickly as possible to keep as much in there as you can, no idea how much extra fluid that ends up being but I was just going to buy a quart and a pump and see how much it took.

One more interesting thing I found is that the 550ix's ATC350 is used in the Alpina B7X, and from everything I can find it is the stock unit with no physical upgrades. The Alpina B7 runs 500hp/517tq and weighs 4500lbs, obviously Alpina is very well known and respected as well as warrantied so this is a good sign for the ATC350!

Additionally if we are stuck with the ATC300, I've found a few shops that rebuild them with stronger chains, bearings, pads, etc so if I go further down that road I'll get a quote on an upgrade.

The reason I haven't done it yet is because the transmission still "feels" perfect, as worthwhile as feelings are to discuss in my head, the aforementioned services would improve the life and performance of the car over the long haul more so than immediately, although there would probably be immediate benefit to doing so at the car's "half way point" or so in it's life span.

Thanks for the method to overfilling it. When the time comes, I'll put it to action. That is good for the possibility of running the ATC350. If they're built to take more abuse than the car delivers in stock form, it should be a good option. Depending on what the correction factor is for crank power to power to the wheels, I might already be putting down 500tq with a 442lb/ft tq dyno reading... On low octane at that (foolish) Depending on fitment and price of the ATC350, a built ATC300 might be the better option though. I await your findings, along with the apparently inevitable destruction of my ATC300

[Doyle]

Quick PSA: if you are over 50k miles, change your driveline fluids. I thought mine were fine, but I flushed everything and the car feels completely different. I did Motul and could not be happier. The transfer of power is soooo much smoother.

Now on the topic of swapping the ATC300 for the ATC350, I think that will be a bit fruitless. But I'm hoping not! First, the ATC300 is gear driven while the ATC 350 is chain driven. I think that might be an issue for the transmission control unit and all the accompanying sensors. Looking purely at software issues, the x5 35ix has the ATC450. However, it has a different transmission, so I'm not sure if there will be hardware issues.

I think it might be more prudent to work with what we have. I'm not sure about what other transfer cases uses a gear/clutch system like we do, but it might be worth looking into.

As far as I know, here are some potential weaknesses & solutions:
-heat: external tc cooler & additional fluid
-friction: wpc coat the gears and clutches, keep fluid cooler
-worm gear/cog interface: machine metal cog instead of plastic

Lets keep the discussion going, because I believe that x-drives could be strip terrors with the right prep!

[amclint]

Awesome information Doyle, was looking for someone with more knowledge to clear things up. I had talked about a shop upgrading the ATC300, but that was based on the fact that they did ATC450s. Now that I know they are different that may not even be an option, chain driven TC are much easier to beef up it would seem.

Also makes sense how some people have killed their TC from a single hard launch, versus a degradation in performance as components fail. The gears in a very hard launch must just be ripping the teeth off.

The ATC450 did seem to have different dimensions but without measurements that's just a guess off those stock images. I may see if there are any local speed shops that deal with the WRX/Evo crowd and ask around about beefing up the diffs and TC on those cars, might have some cross-over knowledge or contacts.

[Doyle]

I'm most curious in how the TC fails. Is it a catastrophic failure like some here have implied? Or is that just hyperbole. Like I mentioned before, there was a pretty common issue with the x3s where the worm gear ground it's threads off:

http://www.e90post.com/forums/showpo...4&postcount=64

Is this the same failure point? If the TC violently redirects power, these teeth/threads may skip/chew up. If so, that is a super easy fix.

If it is a big boom, we may have to look to some differential shops. Since our TC is basically a modified viscous clutch differential, shops that build them might have some knowledge. Diffsonline, for example.

[Beemw335]

Originally Posted by Doyle

I'm most curious in how the TC fails. Is it a catastrophic failure like some here have implied? Or is that just hyperbole. Like I mentioned before, there was a pretty common issue with the x3s where the worm gear ground it's threads off:

http://www.e90post.com/forums/showpo...4&postcount=64

Is this the same failure point? If the TC violently redirects power, these teeth/threads may skip/chew up. If so, that is a super easy fix.

If it is a big boom, we may have to look to some differential shops. Since our TC is basically a modified viscous clutch differential, shops that build them might have some knowledge. Diffsonline, for example.

My friend was ripping it through 1rst and second and heard a pop and then smelt a burning smell. Abs light came up and a few others, basicaly the car drove like a rear wheel drive without traction control.

[Doyle]

Originally Posted by Beemw335

My friend was ripping it through 1rst and second and heard a pop and then smelt a burning smell. Abs light came up and a few others, basicaly the car drove like a rear wheel drive without traction control.

Ok, so not similar to this, lol:

Can you give us some more information? As far as I know there has been no firsthand evidence of torque based TC failures here on the boards...and there are some high powered cars. There have been TC failures, but they were just unlucky individuals trying to get to work.

Mileage on the car? Driving habits of the driver? Power levels? Maintainence schedule/quality? What actually broke within the TC (assuming the shop told/showed him)?

I did some looking into how the r35 GT-R problem was resolved. It seems like the big issue was how rapid the clutches engaged within the transaxle. Cobb worked their magic and the car got faster and more reliable. So, it looks like a hardware and software solution will likely be needed.

[Ferruccio]

http://www.e90post.com/forums/showthread.php?t=641435

This guy seems to have gotten quite a bit of torque off the AWD drivetrain. Does that equate to around 500 ft-lbs at the crank?

[nailer335]

I'm not quite sure what the correction factor is for distributing the power to all four wheels instead of just two. should be though. And that was basically a pump gas pull too (95 octane). I scheduled myself at the same dyno for a week from tomorrow to give it a shot with ms109 and 19psi.

I'll do the pull with an open hood and open downpipes lol

[BES335xi]

I just recently went FBO, havnt done any racing or logging yet but this TC issues are scaring me...i just had my water pump replaced and hpfp...How much do TC run to get em replaced anyway?

P.S Firepoule, love ur yt videos man, subcribed for a long time now.

[Beemw335]

^^ at the dealer tc with labor is 6k

[BES335xi]

Originally Posted by Beemw335

^^ at the dealer tc with labor is 6k

Screw the stealership lol im out of warranty and this got me worried lol...hmm

[nailer335]

no need to worry yourself into not enjoying the upgrades you spoiled yourself with... just log your car regularly and don't do massive brake boosts. keep it easy off the line and I don't presume that replacing the transfer case multiple times will be a problem. I could be wrong on that too. But I have been very inconsiderate to my transmission for 67k miles and it is still holding up without "feeling" like its hurt at all.

[pits200]

Originally Posted by Beemw335

^^ at the dealer tc with labor is 6k

6k for a transfer case install!

[akotten]

One thing I've noticed is that BMW changed their tcase design (part#) for the lci in 2009 when they went to "xDrive". This new tcase is now the replacement part for all xi's (07-11). The older part number is now discontinued.

[amclint]

Good to know akotten, a chance anyway that the new one is more capable since they use it on heavier cars than the 335xi.

Can anyone offer some insight as to an issue I'm having:

Brake boosting the car more than 2-3 seconds it suddenly gives, revving the engine free like it's in neutral and as I come off the gas and revs come down it re-engages.

I had thought it would be the torque converter but after checking with the mechanic that recently replaced my trans, they are saying I have a new torque converter. Also 2nd gear starts it will attempt to get going and then give way also in the same fashion as I'm rolling, but more of a slip feel than a complete disconnect.

[pits200]

Originally Posted by amclint

Good to know akotten, a chance anyway that the new one is more capable since they use it on heavier cars than the 335xi.

Can anyone offer some insight as to an issue I'm having:

Brake boosting the car more than 2-3 seconds it suddenly gives, revving the engine free like it's in neutral and as I come off the gas and revs come down it re-engages.

I had thought it would be the torque converter but after checking with the mechanic that recently replaced my trans, they are saying I have a new torque converter. Also 2nd gear starts it will attempt to get going and then give way also in the same fashion as I'm rolling, but more of a slip feel than a complete disconnect.

That is how mine feels, I've probably only tried 2 or 3 2nd gear launches. It will not grip it and rip it like a 1st gear launch. I think it is too much strain on the transmission/torque converter with those 2nd gear launches.

[amclint]

Originally Posted by pits200

That is how mine feels, I've probably only tried 2 or 3 2nd gear launches. It will not grip it and rip it like a 1st gear launch. I think it is too much strain on the transmission/torque converter with those 2nd gear launches.

2nd gear isn't a good idea for longevity on a stock trans with more than 370whp IMO, but every now and then it should handle it fine and if it isn't then something in the drivetrain is giving way.

I was thinking about it, and before I had the trans replaced I remember brake boost slipping and free revving also, so the component at fault must not be the trans or torque converter. The only other component would be the transfer case, I don't know a lot about them but does it make sense for a worn transfer case to slip like that?

[carsrmilife]

This certainly is a frightening thread to read for me since I plan on installing my WW meth kit in the next couple weeks. At that point, I will be FBO minus an FMIC. I planned on going to the strip to see what she would pull after install, but not so sure now... Granted, I never do anything more than 2k launches.