12 bolt, manual trans, 26.6 diameter tire, car is turning 2200-2250 RPMS @ 55-60 MPH.
3.08 ?
Thanks.

What transmission and what final drive ratio?

M-20 1 to 1

If it is a 3 or 4 spd. with a 1:1 final drive, I would say it is 3.08 with stated tire dia. and speed.

NOT a good way to be sure. :noway: A better way is to get the rear of the car on 2 jackstands after chocking up the front tires, put a white chalk mark on the driveshaft and get the trans in neutral, and count the number of turns the driveshaft makes to every one revolution of the rear wheel when turning it by hand. 3 1/2 driveshaft turns would be 3.55 gears, a hair over 4 turns would be 4.10 gears, etc., etc.... BTW, is it a posi rear? I'm thinking that it probably is since it's a 12 bolt.

pop the cover and count the teeth. the gear oil probably needs to be changed, anyways.

Wire brush the front side of the right hand axle tube, near the carrier casting. There should be some code stamped there. It can be decoded to reveal the ratio.

Wire brush the front side of the right hand axle tube, near the carrier casting. There should be some code stamped there. It can be decoded to reveal the ratio.
unless, of course, someone put different gears in the car sometime in the last 40 years or so.
pop the cover and count teeth- it's the only way to know for sure.