Right now I have a series 2 2.73 rear end. I was wondering how hard it is to change it to a series 3? Is it just changing the diff, ring, and pinion? Or is it something really difficult to do?

 

The difference between a 2-series and a 3-series is the carrier itself. If you sat the two of them side-by-side on a flat surface standing on the end closest to where the ring gear bolts on, and measure to the face where the ring gear actually bolts to, then you'd find that the face on the 2-series carrier is about ~1/4" or so lower than it is on the 3-series. That 1/4" difference allows for the use of larger pinion gears to get higher gear ratios inside the diff (lower numerically).

If you're wanting to change ratios from your current 2.73 to something else, there's no need to install a 3-series carrier.....just buy a ring and pinion built for the 2-series carrier. The difference will be that the ring gear is 1/4" thicker than it would be for a 3-series gear, but it makes no difference otherwise. There are also spacers available to go in between the ring and the carrier so you can use a 3-series gear on a 2-series carrier, but I wouldn't recommend going that route.

 

I was gonna just change the ring and pinion, but I have the chance for a really good deal on an Auburn diff. It is a series 3 though, brand new. So I figure since my cars got almost 120,000 miles on it, it wouldn't be a bad idea to change them both.