Has anyone added an Eaton posi to a 1984 Trans am? what is the rear end in this car/ is it a C-clip, a 10 bolt or 12 bolt? ring & pinion. I so not know anything about this diff. enlighten me.
My T/A is a peg leg & at some point I will add a posi. I had it done to my '72 Buick GS with an Eaton posi in the Buick 8.5, 10 years ago

10 bolt 7.5 ring gear, maybe a 9bolt (not sure if 84 or 85 was the start for 9bolts in birds) or it could have been swapped to any number of aftermarket options. You'll have to get under the car and have a look see..

Today I climbed under the car. I have 10 bolt & I would take to be a GM corporate 10 bolt. Ring gear, I have no idea.
THis car is all original.

Yup, most likely the 7½" 10-bolt. 9-bolt didn't appear until 85 in Firebird and not in Camaro until 87. Not that that would have kept someone from putting one in it; bolts right up; and rear ends are one of the most common different-year junkyard changeouts as cars age. So, just because one didn't come in it, doesn't automatically mean there's not one there. WHich is why getting under it and looking is so important before buying parts.

The 7½" is the only 10-bolt that ever came in these cars. In later years they enlarged the OD slightly, to 7-5/8", but it's still the same rear. In fact AFAIK there are no actual 7½" ring gears available anymore, only the later-model size. Yes it has C-clips; very much the same as the old 12-bolt or the crappy old 8¼" 10-bolt.

That said, it's BEYOND EEEEEEZY to swap out the carrier in that thing, same as any other 10- or 12-bolt. Only thing is, in 2021, I would not use the traditional Eaton clutch-type unit from days of yore. The True-Trac is the way to go in 2021, or, the Zexel Torsen (very similar) from 98-02 V8 Camaro/Firebird. Those are worm-gear systems instead of clutches. Altogether better in many ways.