i have an 86 Z28, what rear-end could i have in my car? Is it a posi?, the car is not running so i cant tell by peeling out.

 

get under the car and count the bolts, most likely a 10 bolt with a 7.5 ring gear. to figure out if it's posi or not pull the cover and look. while you're at it find the ratio stamped on the ring gear and do the math and see what gear set you have. lot of people will tell you a lot of differant ways to check without getting dirty or getting under the car but none are 100% accurate like this method.

 

Yep, and as a bonus, you'll be changing that old fluid for some new fluid.