well this was really something... I was going along route 287 in NJ at about 75 mph when all of a sudden it felt as if I hit a bolder and got stuck on it! look in my rear view mirror, and I see a shower of sparks shooting out the back of the car. Obviously I pulled over as soon as I could. Upon investigation, my diff fell out of the car (still attached to everything) and fell right onto the ground and started dragging. it looks as if the 4 bolts to the frame are what did this. 1 was broken off and the other 3 were missing. So far it looks like what broke is -

Rear differential got punctured by dragging on the road at high speed
Homokenetic joints both broke
rear drive shaft and joints are now questionable
both rear wheels are tilted way wrong, but I think they would re-align if the diff were bolted back up where it should be
and the exhaust got taken out by all this.

I was about 100 miles away from home when this happened, and lets just say AAA was not very fast about getting me a tow 

Anyone else every have this happen? the car is a 1983 300-SD