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      06-21-2012, 09:30 AM   #10
Doyle
Hellafunctional
 
Drives: 335xi
Join Date: Nov 2010
Location: N/A

Posts: 426
iTrader: (2)

Lol, Nailer. Change those fluids! I noticed the biggest difference with the front diff. Motul, all the way.

Anyways, lets have a little refresher on the ATC300, past failures, and weaknesses. Just to get everyone on the same page.

The ATC uses a series of clutches, gears, and servos tied into the DSC system in order to control torque split (max-50:50 to 0:100, f:r resp.).

When the car is turned off, at parking lot speed, or over a set speed, the ATC totally disengages. During normal driving, the ATC sits at roughly a 40:60.

Clutch engagement is controlled in the ATC300 through a servo, attached to a worm gear that in turn controls a cog. That cog then turns a series of gears that control the amount of clutch take up between the front and rear axles.

So, knowing that here are the areas for failure:
-DSC System/Electronic
-Fluid overheating/limp mode
-Worm gear/cog interface
-gear/gear interface
-clutches

In my research, the documented failures of x-drive transfer cases seem to all stem from the worm gear/cog interface (x3's, typically). The main reason is that the cog is a plastic gear that isn't intended to take large loads. The secondary reason is that through normal driving, the cog/worm gear will only cycle through a very narrow range. As such, it is my feeling that this is the first point of failure.

Think of it this way: At a hard launch, the ATC must cycle quickly from 0:100 to ~50:50. Since the worm gear is metal and the cog is plastic, I bet the worm gear will strip the teeth off that cog. It's like stripping the head of a screw when you have your drill set at too high of a speed.

But, people need to keep fighting the good fight and bumping up the power until we see transfer cases grenade. Then we know what we are dealing with.

Rule #1 of racing: if you can't afford to break it, you can't afford to race it.
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