Why do front diffs blow up?

[davew833]

I just pulled the tranny out of my '92 LS-L and the front diff is toast! The case has a huge crack across the bottom and up the left side. I was wondering what usually causes these to fail so catastrophically? Would a bad tranny cause the diff to fail also? I just got this car as a non-runner so I don't know the history, but I'm planning to put a new diff in it. The tranny itself appears to be a rebuild- it's got rebuild markings all over the case and the fluid was clean with no big chunks of anything in it. The car has just over 100k miles.