67-81 REAR AXLE
Two things to know, the final drive ratio and type. For type: limited slip or not.
It's very easy to know what type of differential is on your car, just stop on the bottom side of the road with a wheel on the asphalt and the other in the ground/grass/gravel. Then put pedal to the floor and if the car tends to make the "in-place" you have a standard type. Conversely, if the car leaves well, then there is a limited slip. Or is that your discs differential are dead!
We also frequently talk about of 10 or 12 bolts. This is simply the number of screws holding the crown of the differential and incidentally also the number of screws of the rear cover of the bridge.
The final drive ratio is identified with 2 or 3 letters codes. Below matches.
The 1967 Firebird has the particularity to have a rear axle held by arms while in 1968 rear axle was hold only by the blades/spring of suspensions.
On Gen1, the code is "hit" on the right side of the rear axle (passenger side) with the inscriptions facing the front of the vehicle.
Ratio 1967-1968 1969 Type S L S L 2.56 XB UN XB ZB 2.78 XC UP YC ZB 2.93 XD UR YD ZB 3.08 XE US YE ZE 3.23 XF UT YF ZF 3.36 XG UV YG ZG 3.55 XH UW YH ZH 3.90 - UX - ZK 4.33 - UY - ZM
On Gen2, the code is "hit" on the right side of the rear axle (passenger side) with the inscriptions facing the front of the vehicle.
Ratio 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 Type S L S L S L S L S L S L S L S L S L S L S L S L 2.41 PJ PS PJ PS PJ PS PJ PS-PV PJ PS-PV PJ PS-PV 2.56 PG PT PH PT PH PT PH PT PH PT PH PT 2.73 CRX CRY GZ CA GZ CA GZ CA GZ CA PA PU PA PU PA PU-PR PA PU PA PU 3.07 COS COT 3.08 COE COF GX GY GX GY GX GY GX GY PC PW PC PW PC PW PC PW PC PW-PQ PC PO-PW-PQ PC PQ-PW 3.23 PD PX-LD PD PX PD-PM PX-PP PD PX-PP PD PX PD PX 3.31 COU COV 3.36 COK COL 3.42 CK CJ CK-CL CJ-CM CL CM CL CM PO PB PY-PO PE PY 3.55 COW COX 3.73 COZ CG CG 4.10 CB
L -> LOCK = SAFE T TRACK (limited slip)
S -> OPEN = Standard
Ratio Pinion/Crown 2,41 17/41 2,56 16/41 2,73 15/41 3,08 13/40 3,23 13/42 3,42 12/41 3,73 11/41