I have an RS with a 2 series carrier. What are the primary differences in the 2 and 3 series carriers and will gears from a 3 series fit a 2 series? I'm looking at some used 3.42s. Thanks.

 

Factory gears are not interchangable between carrier series.

 

You can buy 3-series gears (3.23's and up) for 2-series carriers, but the difference is that the 2-series ring gear will be approx. 1/4" thicker than the 3-series ring gear. You CAN buy a spacer to use with the 3-series gear in your 2-series carrier, but you also need longer bolts then, and I can guarantee you that it won't be nearly as strong as just using the proper ring gear on its own, and it'll likely shear the bolts off. I know that happened to a friend of my dad's when he tried using a spacer behind the ring gear.

I'm afraid to say your best bet is either buy a new set of 2-series 3.42's for your car (new gears aren't all that expensive) or look for a complete rear end with 3.42's already in it if you want to go used.