8.2 vs 8.5 10 Bolt Rear

Q: 8.2 vs 8.5 10 Bolt Rear

What is the difference in the two 10 bolts in ’67? Was the 8.5 the posi? I haven’t been able to find an explanation anywhere.

A: As far as firebirds go, all 1967, 1968, and 1969 firebirds had the 8.2 inch rear end. It has nothing to do with whether or not they were posi. The 8.2 inch rear (at least in firebirds) is considered a BOP rear (Buick-Olds-Pontiac). Starting at least partly in 1970 and then from 1971 on (I think) the firebirds all used the Corporate (Chevy) rear end which is 8.5 inch. Again, nothing to do with whether or not it is posi.

Aside from size of the ring gear, 8.2 inch rears also used a different posi unit (cone-type vs clutch-type) which is considered weaker, they attached somehow at the end of the axle near the bearing (haven’t taken the time to figure exactly how yet) vs the 8.5 which use c-clips inside the carrier, plus other differences.

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