I am currently moving up the ladder from a open diff 2.73 to a GM posi 3.55 that came stock in another car. Would anyone happen to know off hand what the drive and driven gears would be that came stock with these gears?

Thanks

Don't know for sure what came stock, but if you are looking for a speedo gears, Rick's has a small chart in the catalogue that helps you decide on the correct one. It's easy to determine and the swap is simple. Kevin

I followed that chart and bought the correct gear for my 4.56 rear, but the gear is too large to fit into the hole in the transmission.

It all depends on what transmission you have and what drive gear is in there. I did the swap from 3.08 to 3.55 with a PG. And used the charts on novaresource.com, then bought the correct number of teeth. Worked fine.

X33D80. The drive gear teeth number changes around where 3 series jumps to 4 series. You will have to change the drive gear too. The large diameter driven gears are for TH400 if I remember. The small driven gears are for muncies, PGs and TH350s, which I am assuming you have a muncie.

That explains the size issue. How difficult is it to change out the drive gear in a Muncie?

Hey, thanks for all your advice and answers. I forgot totally to add that this was for a th350. But anyway, TCI has a calculator that takes gear size, tire size, and trans and calculates what works for what gears and trans.

Sorry for the mispost also. I also did not realize this specific forum was here.