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I have a 10 bolt rearend in a parts car 1981 el camino. I jacked up the rear end and spun the rear tires, only the the one I spun turned. the other one stayed put (but the driveline turned) I did the same to the other one and got the same result. (both tires were off the ground) Do I have a posi 10 bolt? or just a messed up rearend?

Also, could I just bolt this rearend into my 1968 el camino (10 bolt also) if it is posi? or would I need to change the mounts. Could I just take the ‘pumpkin’ out and swap if not?

If it is a Posi, it is worn out or damaged. On a good working Posi, both tires will spin equally with that test. Or you have a standard differential without Posi. If the transmission is in ‘Park’, the other tire should spin in the opposite direction with a standard diff with no Posi.

I’d check to see if the mounts are the same in order to see if the axles will swap out. 13 years is a lot of time for Chevy to make changes. The mount positions and bushing holes would have to measure the same to make it work.

Also, changing the pumpkin would require the new pumpkin to be shimmed to the old housing, which is a specialized and time-consuming task. And is more difficult if the gear ratio is different, requiring the ring gear or the pinion gear to be swapped to match. For a shadetree mechanic, changing out the rear end is an easier and cheaper task.

It’s NOT a Posi, the rear end is FINE…That’s what open differentials do…With a Posi rear end, BOTH rear tires will turn in the same direction…

And if you hold the driveshaft, the other wheel will turn the opposite way.