Originally Posted by bvanderbilt
Someone needs to explain how something which caused 1/8" abrasion on the side of the differential was able to deliver enough force to shear to a 10.9 bolt. Even a high school physics student is competent enough to provide proof that is impossible; as others have stated the impact area would be far larger and the differential cover destroyed.
The real cause of the bolt failure can be established by a failure analysis test in a laboratory. I'm sure by now the bolt has been put into the scrap pile by BMW and it is too late. If this happens again to anyone else make sure you get the failed bolt once the repair has been done.
The failure analysis results will provide material strength test as well as what torque value was used on the original assembly. Torque wrenches have been known to be out of calibration by repeated use, the slightest movement of the adjustment barrel will change the torque value drastically.
Bottom Line; should BMW on a failure like this ever deny you warranty ask for the failed part and tell them
"Fine let me have the failed parts and I will have them analyzed" If you are right fine, however, if improper workmanship was the reason for this failure I expect you to pay not only for this repair also for the failure analysis" They might change there tune ... Stand your ground fellows don't take everything for granted ...