I've just done this replacement on my X5. Here are two things I noticed from my experience.

1. If you have the three warnings lights on your dash (ABS, Brake and 4x4) you won't hear the motor gear clicking under your car as it disables the unit until errors are removed. My gear must have been slipping to begin as occasionally all the error lights vanished and I could hear the clicking of the gear again.

2. Prying open the the case to access the gear can be difficult and you need to use WD40 to help pry open the case.

3. Make sure you clear all the old grease/gunk out of the case before installing the new gear. Also, replace the grease with some new product and ensure it is applied to the long gear and the gear you are replacing.

4. If you can feel a slight lag or movement of power from front to rear on acceleration, replacing this gear may solve your issue. Just before it failed I had this issue, after the replacement of the gear the issue was gone. I'm assuming the gear was slipping and the car was unable to engage the clutch inside the transfer case quick enough.

5. I had wear on both the top and bottom side of the gear, I would suggest replacing the whole gear rather than simply flipping it over.

6. The sensor that you remove before you unbolt the motor from the transfer case has a lip and it sits along side the dip in the motor and locks in place as you tighten the nut (I struggled to figure out where it went as I had low light under the car during this procedure).

Hope these tips help.

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2007 E70 X5 3.0D Black/Beige - SOLD
2012 E70 X5 40D Silver/Black