There's a couple of misconceptions going on here. First, strictly speaking, posi doesn't belong in the same sentence with our trucks. Posi is short for positraction, which is GM's name for a limited slip rearend in a GM product. A "posi" is not a magically better anti spin device, it is just a normal clutch type limited slip unit in a gm rear axle.

I don't nitpick at people for using the term posi anymore-almost everyone does it, and everyone knows what they mean when they do. Let's just be clear, a posi is not some super duper limited slip unit.

The other thing is, when it comes to changing carriers, whether you have to depends on which gears you're going to and which gears you're going from. Where that breakpoint is varies from one rearend type to another. This is commonly referred to as a "carrier break".

The "2 ratios and you're safe" idea is actually not true. Here's an example of why: Let's say you have a rearend where there's a carrier break between 2.73 and 3.08 gears. You have 2.73's and want to swap to 3.08's. You must change the carrier to do this. Put differently, going from ANY gear on one side of a carrier break to ANY gear on the other requires swapping carriers. (unless you get some special gears that have the ring gear made extra thick or thin to account for the difference between the 2 carrier types, in which case you don't have to swap carriers.)


Now, here's the good news: As far as I know, 9.25 chrysler rearends have no carrier break at all. Not all rearends do, which is nice when you have one of those types and want to make a gear change.