ok so i have a 89 firebird with a 350(orignaly a 305 was in it) and i have quite a few upgrades to the engine my problem is im working with the 1 wheel wonder. I need too find a posi and was wondering wut rearends/posi will work out of which gm models and years will fit in my 89 firebird. I was reading that maybe the blazer or a s10 posi would work can u list a few models i can get a posi from for my bird that would have decent gears in it

true the s10/blazer (and many other gm cars and trucks) had the same 7.5" 10 bolt rear as your bird but i dont know of too many that came factory with a posi maybe some with a hypo option if you dont have the money to buy a posi unit from jegs or summit, ect.. go to your local savage yard and start looking for 10 bolts with a steel tag hanging from one of the bolts these generaly are what your looking for write down the info on the tag and google rear end tag decoding youll find something.

then when you find the right one (a 7.5" with the same spline# as yours i think they are 26 ) most yards will not sell you just the center section they want to sell the whole rear (only a rear from an fbody will "bolt" in) youll have to swap out the center section

or if your lucky and find an iroc or gta and several other models from 86 to 90 came with a 9 bolt borg warner rear end that was a posi and came in a few different gear ratios fyi the all had rear disc brakes

good luck

Save your money and buy a new posi. After all the screwing around, any factory posi with over 20,000 miles on it is going to slip anyway.