Ok, probably going to take some heat on this, but here it goes anyway.

I have a AMC 20 with a Detroit Locker and what looks to be other than stock gears in it. I’m planning on parting out the axle and want to know how to figure out what the gear ratio is.

Number of teeth on the ring gear divided by the number of teeth on the pinion.

Usually there is a number stamped on the ring gear, like 41-11, which would be 3.73. Divide the big number by the smaller one.