Im sure its been asked a million times, but how do you determin the gear ratio of a rear end, i know ive heard its stamped on the tube what am i looking for? I want a 3.42 posi rear, drum or disk, so help me out.


Also one other question, how can i tell on a fourth gen rear and can my 3rd gen wheels fit on a 4th gen rear? thanks

 

to be 100% sure of the ratio pull the cover and look. to tell a 4th gen rear it'll be wider than a 3rdgen by a few inches and have 28 spline axles

 

You need to look at the front of the right hand axle housing, right next to the diff housing. The numbers may be covered in rust, so be sure to have your goggles on so you can wire-wheel the rust off.
Codes are:
1982: 2JJ, 2KH-Standard
2JR-Posi
1983: 4JJ, 4KJ-Standard
4JR-Posi
1984: 6JJ-Standard
6JR, 6PR-Posi
1985: Same as '84
1985 Borg-Warner: No code, part numbers 14085324 and 325 are Standard.
1986: 8JC, 8KA-Standard. According to source, no Posi's for this year.
1986 B/W: None in 3.42 ratio according to source.
1987: 2HL-Standard
2HR,4HR-Posi
1988-9: 6HL is only 3.42 and is Standard.
1990-92: 8HC-Standard
2PN-Posi.

The brake situation has to be determined by visual inspection. If 4th gen brakes fit on 3rd gen axles (with adaptors to increase spacing), I am pretty sure 3rd gen wheels fit on 4th gen axles, but I do not know. And I am sure that fourth gen axles are found on fourth gen cars.

Notes: 1. Owners of cars may have changed the gear ratios in their rearends, so the only way to be absolutely sure that iy have a 3.42 rear is by visual check of gearing.

2. Information was taken from an 82-92 Firebird Haynes manual, and judging by what else is wrong in there, I cannot be absolutely sure that these codes are correct.