I just found an 8.5'' posi unit out of a 79 Trans Am and I would like to Know what ratio that it is.The Pinion has 13 Teeth on it and the ring gear has 40 teeth on it,could someone tell me the ratio of the rear end ,,,,Thanks Camaro BOB

40 divided by 13 = 3.0769 = 3.08

Which makes it a 3 series posi.

Hey guys ,I have a couple more ?'s on the Posi unit that I got from the Trans Am.How many teeth does the ring and pinion have for a 342 gear,and are the axles from the Trans Am the same length as the Camaro or they longer ,,,Thanks Camaro BOB.....

I think it's a 41 tooth ring and 12 tooth pinion.

If you are talking about using the posi, gear set and axles in a second Gen 10 Bolt, the answer is yes. However, they will not interchange with a 1st Gen 10 Bolt.

Guys the housing that I am using is out of a 73 Nova ,I have an article out of the Jan. 2001 Chevy High Performance Mag. that says you can use the 8.5 posi unit out of ,say ,the Trans Am and be able to use the axles backing plates drums and all the related brake parts out of the 8.2 rear.What I'm asking is ,is the axles out of the Trans Am the same length or are they 1'' longer,I know I can use the ones out of my 8.2 that came in my 68 but if I can get by without tearing that thing down the better off I'll be.Any Help Thanks Camaro BOB,,,,,,

The Trans Am rear end is 1 inch wider than the first gen Camaro rear end, and the spring perches are about 3 inches farther apart.