A friend of mine recently aquired an 1989 T/A with Performance suspension badging. We are unsure whether it has a posi unit or not. I heard there is a way to determine if a car has a posi by jacking up the rear end and rotating one tire and observing which way the other tire turns. Is this really a way of determining if you have a posi? and if so which direction of rotation indicates it is a posi?

 

Yup, jack it up.. spin one wheel and if the other wheel spins in the same direction, good chance you have a posi Another more fun way is to go for a drive, stop in the middle of no where and lay down some rubber 2 black lines = posi 99% of the time

 

Thanks, I recommended the second technique to him but he currently has a broken trans mount so he babying the car till he gets its replaced.

 

100% for sure way is to pull the cover and look, and while you're there you can figure out what ratio you have, then change the oil and posi additive, if it is posi.

 

My 82 used to do 2 tire burn-outs about half the time with an open rear 3.08's. Not a good method if you want to be sure. Like he said above, pull the cover and look. While you have the cover off you can verify the gear ratio as well as the posi. Chances are it needs to have the fluid changed anyway. 2 quarts of diff fluid and a little rtv silicone are the only costs.