I broke the front planetary (4 pinion, if my memory is correct) on a 904 years ago, it made a nice boom when it broke. All forward gears were gone, but reverse worked fine. In my case the planetary was steel with a welded on "collar" with splines that engaged the output shaft, I'm guessing it was an OEM planetary. The weld had poor penetration and/or cracks formed and that's where it broke.