How can I tell these two carriers apart? I have a posi carrier from a 94Z that doesn't have any gears on it and I need to know if it's a series 2 or series 3.

 

do you have access to the 94 Z?
Do you know if it was a manual or can you check the build codes?

 

Unfortunately, in all the time I've messed around with 10-bolt diffs, I've never actually taken the measurement of the distance from a flat surface, to the face of the flange that the ring gear bolts onto . That face is off-set by ~1/4" one way or another, depending on whether the carrier is a 2 or 3 series. That's the only difference (it allows for larger or smaller pinion gears, which is dependent on the high/low ratio).

As 'Style' already pointed out, if you know what car this came out of (specifically with reference to whether it was a 6-speed or an auto, and then if you happened to know what ratio it had, if it was an auto (2.73 or 3.23)). If it was a 2.73 auto, it's a 2-series. Otherwise, anything else and it's a 3-series.

UNLESS it came from a 3.08 geared V6 Camaro, in which case it would also be a 2-series .

 

Nope, no access to the other car, that would be to easy.