my 1986 iroc-z has a 323 posi. i want to upgrade to 373 gears. my problem is the car only spins one wheel.Is the stock unit worn out? can it be rebuilt?Should i just buy a auburn,or other brand carrier.

 

sounds worn out to me. i'd replace it even if it could be rebuilt. you can buy a slp for 100 dollars and a set of axles for less than 300

 

Sounds like it's either completely worn out, or it really isn't posi in the first place.

Take off the cover and look if you haven't already. Don't trust any other method for determining what gear you have or whether there's a posi in it. Once you know what you really have by looking at it (as opposed to what these various "tests" make you think, or what the car's original paperwork says, or what the "codes" say, or whatever) then you'll be much more able to make the right choice about what to do.