8 3/4 axle out of c-body

Did you put the trans in neutral? Or take of the driveshaft at the rear end, and try to rotate the yoke.
If the driveshaft is blocked by the trans, and the wheel you were turning went in the opposite direction of the wheel on the other side, it means you have a non-sure-grip diff, or a sure grip that's completely worn down. If it's the first, there's probably nothing else wrong, other than probably some worn bearings.

Antoon