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Honestly, I wonder if this is a software issue.

The front diff is a full time locked differential, with the slip for wheel differential (for turns) happening inside the transfer case. The clutches happen to be very strong inside the transfer case, and if the transfer case actuator is programmed to be aggressive, the extra differential speed may be putting stress on the output flange.
I have a close contact at BMW engineering and I will ask him to see what he can find out as well.

I find the ATC35L a robust transfer case with good build. Especially when compared with old transfer cases with plastic gears and things.
I wonder if running it in 2wd mode (coding or disabling things) is protective to the flange.

I am at 79,700 miles, original 27107505374 case built Sept 20th, 2013. My last 9000 miles have been using strictly rear wheel drive only, through disabling the VTG module, and tuned with more power.


I was preparing to start my own thread for analysis... but there is no reason, now that I was directed to this thread.

This is what I was going to post to try to prove my hypothesis:
Use for ideas if nothing else.





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If you have a 4wd BMW with the ATC35L transfer case, I invite you to participate in this data collection.

*It is important to have documentation of transfer case failures, as well as data on cars without transfer case failures, for a control group*



Data Collection

Having very accurate data is critical to sorting out clues as to what may be causing the failures. I ask that you post in the following format, for each transfer case failure event, or if no failure in your F3x, then fill out information about your car.

A. Basic Car Info

1. Car Year and Model:
2. Last 7 of VIN *(needed to check car options/production date, can be sent by PM if desired):
3. Current Mileage:
4. Total Miles owned:
5. Sports Automatic Transmission Software ("2TB" option, or retrofit): Y/N
6. Known software updates to car:
7. Current I-Level (if known):
8. List any Maintenance to Driveline (oil changes, etc):
9. List Mods Done to Vehicle (Extra power, different size wheels, etc):

B. Driving Habits/Conditions

1. Driving Mode Used Mostly: (ECO PRO, Comfort, Sport, Sport+)
2. Driving Style: (Relaxed, Moderate, Aggressive, Racecar)
3. Automatic Gear Shifting or "Manual":
4. Type of Driving: (Highway, city, mixed?)
5. Describe the terrain/landscape it is driven in:
6. Any Towing with the car:

C. Transfer Case Failure

Number of Known Transfer Case Failures: (for each failure, describe below, separately. If 0 failures (control group), please skip below.)

1. Mileage at failure:
2. Component That Failed: (if known)
3. Method of Repair: (dealer, privately. Replaced transfer case, or just output flange?)
4. Part number/date of manufacture of faulty transfer case: (if known)
5. Part number of replacement transfer case:

If you have had multiple failures for the same car, please list each separately!

Please add any other information that you consider relevant with great detail.




If you have had NO transfer case failures on your F3x, please fill this out as well, for data control and comparison. Control data is just as important!