[mwat]

Any launches? Would you say you're easy or hard on your car? I've always heard the diff's are pretty solid. Sorry you had some bad luck.

[MrSeabass]

Originally Posted by mwat

Any launches? Would you say you're easy or hard on your car? I've always heard the diff's are pretty solid. Sorry you had some bad luck.

*Very* easy on the car. This looks more like an issue that gradually got worse over time. I'm waiting on a 30mm socket to arrive to get the pinion out for a final verdict, but so far it tracks that the bearings got loose and the acceleration/deceleration gradually pushed the pinion into the differential.

[mwat]

Originally Posted by MrSeabass

*Very* easy on the car. This looks more like an issue that gradually got worse over time. I'm waiting on a 30mm socket to arrive to get the pinion out for a final verdict, but so far it tracks that the bearings got loose and the acceleration/deceleration gradually pushed the pinion into the differential.

Man.. sorry to hear. Things happen I guess. Good luck.

[MrSeabass]

Ok final update. Got the unit completely apart and have roughly pieces together what happened. The failure started at the bearing closest to the driveshaft (rough example of the location here)



So apparently BMW uses ball bearings with plastic cages. Here's how a used but working one looks.



And here's what the bearing cage looks like when it breaks apart.



Without a cage, the bearings are free to roll however they'd like, which will cause rapid wear and disintegration of the bearings/races, and also allows a lot of play in the shaft. Here's what damaged bearings look like after they get loose.



Now that all of the tolerances are loose, the bearings will move to wherever they can, causing the races to wear or round over completely as seen in the two boxes showing badly damaged races.



This causes the bearings to finally escape, causing the pinion gear to get shoved into the diff and also some bearings to get caught in the spider gears, which leads to kaboom and money.



As for the root cause, it was likely just a stress failure in the shitty plastic bearing and not necessarily a loss of fluid or extreme driving conditions. All in all, I now have a couple of really heavy desk paperweights and a trash can with a collection of components that I may or may not have spit upon.

[HPR]

Unbelievable. Kind of boggles the mind that such a poor engineering decision (if it was that) would be made in part selection. I wonder what other "easter eggs" are hidden throughout the vehicle.