What would happen if the rear differential failed?

Back in my youth, I did a roll-back burnout in my car which had a single-spinner diff. I heard a loud bang, then everything seemed OK. Myself and my wife drove the car for 6 months (!) without hearing or feeling anything out of the ordinary. Then one day when turning right, I gave it a bit of throttle and the rear end stepped out in a big way like it had a spool, which it wouldn't normally do and I heard the same sort of bang. It got me home, but by then it was making really loud noises and would lose drive momentarily or lock up when turning corners. Sure enough, the diff was rooted! When I pulled the centre out, there was nothing left of the spider gears, it was all just one big blob of broken metal pieces. There were also teeth missing from the crownwheel and pinion.
 
I've seen a few open-wheel diff's lock and unlock randomly shortly before failure. On old Commodore's, a Celica and a handful of other cars. All of them were abused, burnouts etc. Almost exactly like Chichie says. Sometimes they last years, sometimes minutes before failing completely. Can be very dangerous for the diff to lock unexpectedly though.

Listen for any unusual knocks from the rear, check and replace the diff oil. If metallic grit comes out, it may be buggered. Be very careful if you think this is the case.
 
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