'81 camaro rear end with 3:42 gears

I found a rear end for sale i want to buy, the guy said its off of a '81 z-28 with 3:42 gears, how can i tell if it is a posi rear end?  

spin one axle...  if posi the other axle will spin the same way... and the pinion yoke will spin...

if it is an open diff... the other axle will spin the other direction and the pinion will not spin...  

Even if it's not a posi, that's a good 8.5" 10-bolt rear you can build into a strong piece.

If it really is a Z/28 rear, it should have a posi unit.  

so ifnit is an open differential what are the pros and con s of an open?  i have a 1991 rs that everybody i asked said should have posi but when i got it off the ground and did the test the other wheel spun backwards>  i  didn't watch the driveshaft but im sure it porobably is an open if its nto posi.  so is an open no good> ia have put a set of 4.11:1 motive gears in it.  is that going to be okay with the open?  

chevyguy78:
I found a rear end for sale i want to buy, the guy said its off of a '81 z-28 with 3:42 gears, how can i tell if it is a posi rear end?

I am wanting to put it on my '78 camaro LT. The one on my car isn't posi with only a 2:73 gear. if it is an open, is that still a posi too? someone told me that if you put it up and spin one wheel and th other spun the opposite direction then it was a posi?  

good question.  because it would seem to me that if one wheel spins forweard and the other spins backward that would help you corner beter,  but i would not be any good for getting off of the line.  

i finally went and picked up the rear end i was talking about in this thread, i spin one axle and the other one does not move, but the yoke moves. same thing happens if i spin the opposite axle. could this be a limited slip posi rear? if not what do i need to make it a posi, or limited slip posi??  

pull the cover off and LOOK..........

or get the axle code off the axle......  

that is eithe ra open differential or your clutches are gone.  you need to take the cover off and look.  

Sounds like that's an open rear.

Back in the day, road racers would sometimes prefer open rears because the factory posi units would bind and cause handling issues. But today's aftermarket posi units have overcome this.

That's a good rear to have, and will bolt right up to your '78.