i have an 85 trans am with a 700 r4 tranny and i was wondering how i know if the rear end is posi-trac?? also iv heard alot of people talking about changing the gears and stuff, what does this do for you?? thanks alot

theres a few ways to find out if your car has posi. One way is the jack up the rear of the car and then turn your wheel in the direction that it would if you were going forward. If the other side wheel spins in the same direction as the one your spinning you have posi. If not? and it spins the other way? then you dont have posi. Another way is to do a burn out and see if both tires are spinning. If you dont have posi only one tire will spin and the other will just lock up.

Changing the gears will either make you accelerate faster or have a higher max speed. Its pretty much up to what gears you put into the car.

only 100% sure way to know is to pull the cover and look, forget all the other methods and pull the cover.

I like the burnout idea, might be fun. is there like a tag on the diff. I heard that some posi's have tags on them, or something.

Count the cover bolts. If there's 9, it's a posi. If there's 10, it could be either. Forget the tag, pull the cover and look.

Have you changed the fluid lately? Then it needs it. Pull the cover to drain the fluid, look at the carrier while it's off, put new synthetic fluid in it and a bottle of posi additive if it turns out to be a posi.

Also Posi-Trac (GM name for) is a Limited Slip.