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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > Transfer case front/rear gear ratios



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      01-28-2021, 05:21 PM   #1
Brian86
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Transfer case front/rear gear ratios

Anybody had one of our transfer cases apart and counted teeth on the gears?

I have a spare ATC 300 sitting on my garage floor and the front output appears to turn a little slower than the rear.

Not by much, perhaps 149:150 or 199:200 F\R shaft rotations.


It makes logical sense to me that the front output should turn a little slower. That would ensure the front driveshaft is (almost) always applying driving torque to the front wheels via the slipping wet clutch. If they were exactly 1:1 it would be possible for the rear wheels to drive the front wheels and push torque backwards into the wet clutch if perhaps tire pressures are too far off. Plus floating exactly 1:1 would introduce chatter and vibration as the driveline lash is taken up one way or the other.


That said it's a little hard to tell on the workbench if I'm getting clutch slippage. Particularly when spinning the front output and counting turns on the rear output.
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      01-29-2021, 04:51 PM   #2
ewicky
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Interesting. I have a spare transfer case with a snapped output shaft peg; I'll take it apart sometime and if I remember, I'll report back.

Though I'm fairly certain it's 1:1.
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      01-30-2021, 11:28 AM   #3
Brian86
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That's my plan as well. Someday when I'm in the garage looking for something to tinker with I'll open it up to satisfy my curiosity.

Unfortunately free time to tinker has been hard to come by lately.
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