I think I can get a good deal on a 9 bolt Borg Warner posi rear end from a 1987 Trans am with a 350. Tech boards say this is a 3.27 gear ration and I currently have a 3.08. I read this and it says something about needing a pretty expensive 3-spline part if swapping from 3.08 to 3.27. Does this include me? Would I need any other parts?

 

Nothing really special, just make sure you get the proportioning valve and the parking brake cables from the donnoe car.

 

Nothing special like mentioned. I went 9 bolt to 10 bolt. I actually used all my 9 bolt brake parts (rotors, calipers, lines) minus the brackets on the 10 bolt when I swapped them. I had to rebend the lines a little bit.

Your 10 bolt posi, gear set, axles, and etc will not swap into the 9 bolt

You should be able to tell the ring gear size by pulling the cover off and spinning the ring gear around it should be stamped right on it. It's always a good idea to check anyway. You wouldn't want to pay for it then find out some teeth on the gear are missing.

Parts should only be needed if you go from a series 2 to a series 3. If you start at 3.27 9 bolt you'll be fine.

Another thing to check is that the posi unit working properly. That's also discussed in that thread.

 

I made this swap a few years back and it is not a big deal.The nine bolt rear will bolt right in where the ten bolt is. The different gear ratio will require that the speedo driven gear will have to be changed. As mentioned above, some changes might have to be made for the brakes.