I've been told that my iroc z-28 has posi, however when leaving my mark in various places, sometimes its two tires and sometimes its one? Does the rear end need a fluid change or is it just not posi? The car sat for well over a year and a half........check my garage for more info....

Thanks,
Steve

 

Its possible that the diff isn't fully locking due to its age, or wear of components. In either event, you can jack up the rear end suspending both rear tires, turn one of the axles... if the tires move in the same direction, its a posi, if they turn in opposite directions, then its an open rear.

At least I think that theory works on modern posi diffs.

Oh, and obviously the car needs to be in neutral.

 

thanks....I gott fix the heater hose I blew then Ill let you know

 

okay it is easy to tell... inside the center console there is an RPO sheet a bunch of alpha-numeric combos of 3 look for G80 that is for posi and a GU3 or GU4 for the gear ratio either 3.08 or 3.27 you can also look at the diff cover there should be a tag that says BorgWarner or a tag that says use posi fluid or something to that effect

 

well....I couldn't find that sheet you were talking about so I crawled underneath and it said "Use Limited Slip Diff Fluid Only"

 

I'll give the same answer as all the rest of the incessant redundant "do I have posi" threads on the forums. That REALLY REALLY should be a sticky, so that maybe people will know to not ask that and instead go do the research.

The ONLY WAY to know for sure what's inside your rear end, is to take off the cover and look. Everything else - codes, tags, stripes, spin-the-wheel, ALL OF IT - is nothing but guesswork. Some might be better-educated guesses than others, but all are still guesses just the same. In a 20-year-old performance car, there's NO GUARANTEE that whatever rear end came in the car, or whatever parts came in the the rear end housing that's currently in it, is what came in it.

Have you changed the fluid lately? I suspected as much.... so while you're catching up on the overdue basic maintenance and you have the cover off anyway, make a point of looking in the carrier and see if there's springs and clutches in there, or basically, anything besides a shaft and some gears. If there's anything else, then it IS posi, and you do indeed need to add the limited-slip (posi) additive.

And to avoid yet another incessant redundant post, "what gear ratio do I have", look at your gears as well while you're in there. Find the stamping around the edge of them, or count the teeth if you can't find the stamping.

 

Well.......your help is greatly appreciated and I am the second owner and the car has 64k orig miles.......sticky would be nice