What are the physical differences in these two carriers? I have an Auburn posi I bought barely used and want to make sure it is for my 3.23 and up carrier. My original bearing races fit and the length from race to race is the same. What else should I look at?

I am installing it with Superior 28 spline axles and Richmond 3.73's.

 

The difference between series is the location of the ring gear flange; specifically, the lower-number series has its ring gear farther from the pinion.

Think about how gears work for a minute. If they're a different ratio, they not only have to have different numbers of teeth, but the ratio of their diameters must also be different by the same factor as the teeth count. So, since the ring gear diameter is constant, the pinion must get larger as the ratio decreases. Eventually you get to a point to where the pinion becomes so large that the ring gear would have to be too thin to be adequately strong; at that point, they step the flange over away from the pinion, and start over with a thick ring gear.

That's why you can buy extra-thick gears, or spacers, to move a higher-numbered ring over toward its correspondingly smaller pinion; but you can't possibly do the opposite thing to put, for example, a 2-series gear onto a 3-series carrier in one of these cars.

 

Thanks. Nice explanation.

I just realized you live in Loveland. I am moving to Cincy in the next month or two, as soon as we find a house. My future wife lives in Landen/Montgomery right now. Small world.