Trying to be certain of what I just picked up:

I know it is an 8.5" but here are the numbers:

casting # = 1254333
casting date = I 27 7 (last digit is a little ground down but I'm fairly certain it is a 7) so September 27th 1977
Axle tube stamp = 2 PT G82721 where PT = 2.56 posi (a series 2 posi carrier is in it) G = Detroit Gear and 82721 should equal a day of the year and the shift it was built but that if "8" equals the then "272" is the day (September 29th) and "1" equals the shift. there is no posi source code

but here is a problem: PT is not a valid code for '78 camaros and 2.56 is not a valid ratio for '78. they are valid for '77 or '79 yet a cast and build date of september '77 is too late for '77 model production isn't it??

I'll edit and post photos later.

Any insight would be appreciated.

Pontiac used the same codes on Firebirds as Chevy used on Camaros. I don't have a list of the 78 Firebird codes, but the 2.56 posi was probably the most common ratio for the 78 TA. There is a good chance it originally was on a TA.

Pontiac used the same codes on Firebirds as Chevy used on Camaros. I don't have a list of the 78 Firebird codes, but the 2.56 posi was probably the most common ratio for the 78 TA. There is a good chance it originally was on a TA.


That is a really excellent thought Gary - I'm going to pursue that line of reasoning a little.:bowtie:

Rear Axle Identification CodesAxle Ratio Code 2.41 PS 2.56 PT 3.08 PW 3.23 PX or PP 3.42 Unknown All ring gears are 8 1/2" and have positraction

I copied the above information from Gary Lisk's Trans Am 1978 page.
Pontiac did use the PT code that year.
http://www.2gta.com/

Rear Axle Identification CodesAxle Ratio Code 2.41 PS 2.56 PT 3.08 PW 3.23 PX or PP 3.42 Unknown All ring gears are 8 1/2" and have positraction

I copied the above information from Gary Lisk's Trans Am 1978 page.
Pontiac did use the PT code that year.
http://www.2gta.com/
Thanks for the link Gary.., I found similar info at a Firebird /TA site: http://www.78ta.com/rearcodes.php....good call on your part:)

Gary, is there aaaaaaaaaaaaaaaanything you dont know?:eek: Amazing! Love this site!

Gary, is there aaaaaaaaaaaaaaaanything you dont know?:eek: Amazing! Love this site!

Yes, there are lots of things I don't know. I learned a little about rear end codes some years ago when my Son wanted a 3.42 posi for his Z28. We jacked up 15 or 20 Trans Ams at the junkyards to read the codes. After crawling in the dirt under that many cars and finding 2.56 gears about 95% of the time, it sticks in your head.
(We did eventually find that 3.42 posi we wanted, but it was in a Z28)

The Pontiac thing should have been my first guess...and it should have been a no brainer for two reasons:
1) I knew about the shared axles with Firebird but just didn't think to apply that knowledge:o
2) Pontiacs always have higher gear ratios since, from the factory, they are torque monsters and not high rev'ers. In the stock Ponitac world 3.55:1 is a really deep gear set:D

FWIW, this rear still has the 2 series carrier but is packing a 4.10:1 ratio (and spacer ring;) )