Ok, so I'm casually on the hunt for a posi for my 72 cutlass. My question is what am I looking for so that I know that it would fit?
I found an 8.5" 10 bolt posi from a caprice police car but that's a bigger car so I don't think it would fit. Should I be measuring width from one point to the next? Should I be measuring mounting points? Etc etc..
Please enlighten me as to what (everything) that I should be paying attention to.
If I put one in from a wider car would it just make the wheels sit out farther or ??
If everyone gives me their $.02 I might get out of here with a buck

 

You should contact monzaz on this site. (Jim Mitschke). He is an expert on differentials as he owns J.D. Race & Restoration. I bought my posi from him and he was extremely helpful. The posi will depend on what gears you are installing.

 

The only axles that will bolt into your car are those from a 1968-1972 GM A-body car. Those are Cutlass, Chevelle, LeMans, Skylark, and derivative models. NOTHING else will bolt in, so don't waste your time looking at Caprice or other cars. Your car does have the "corporate" 8.5" axle, so the posi carrier and gears from other cars will swap into your housing if you want to go to that level. Note that the axle spline count will vary, so any replacement carrier will need to have the same spline count as your current axle shafts.

 

I did see the "guts" somewhere (Auburn posi) for 150 bucks but I have no clue as to the spline count and sadly I think that was 12 bolt and I have 10. I guess I'd have to open it up to figure this out or could I tell from stamping?

 

An aftermarket "ten bolt" carrier could be 7.5", 8.2", or 8.5", so you had better be sure you know what you are buying. If your car has the original axle, it is an 8.5". You can pull one axle shaft and count the splines, typically 28 or 30.

 

If it's a 72 original axle it will be 28 splines.