TAC Tech => Number Crunching => Topic started by: SP Steve on December 16, 2021, 04:57:37 PM

Title: decode my 74 Trans Am rear end?
Post by: SP Steve on December 16, 2021, 04:57:37 PM
I'm working on restoring the bottom of my 74 Trans Am and installing new suspension. I'm having trouble decoding my rear end it has the code CG G115 2C(G). The only thing I can find with a CG ratio is a 71 or 72 rear end.  If someone has the knowledge to clarify this I'd appreciate it.
Title: Re: decode my 74 Trans Am rear end?
Post by: Maxthe222 on December 16, 2021, 09:31:04 PM
Chevorlet gear and axle diff built on the 118th day of 1972. 3.73 posi rear gear ratio.
Title: Re: decode my 74 Trans Am rear end?
Post by: SP Steve on December 18, 2021, 01:32:03 AM
Chevorlet gear and axle diff built on the 118th day of 1972. 3.73 posi rear gear ratio.

Thanks! I didn't think it was original to the car, but that's not a bad replacement.
Title: Re: decode my 74 Trans Am rear end?
Post by: roadking77 on December 18, 2021, 07:31:02 PM
Someone with the real answer can correct me but I think that it may be correct. I thought that some rears were chevy. For some reason I think the one on my 77 is, but its been awhile and I would have to check the code again.
Title: Re: decode my 74 Trans Am rear end?
Post by: Maxthe222 on December 18, 2021, 10:06:47 PM
Well sort of, the 10-bolts in the Firebirds are called "Chevrolet gear and axle" diffs, but there wasn't anyone else making differentials, which is why they call them a "Corporate GM 10-bolt". That's all GM offered. GM likely did it for the same reason why the 305 chev was the only motor available in the 80's, it was the cheapest. GM didn't even bother making axles anymore after 1981, they outsourced to Borg Warner, a local Australian company and manufacturer. Likely was cheaper, but we paid the price in an axle that wasn't durable under high power.
Title: Re: decode my 74 Trans Am rear end?
Post by: firebirdparts on December 19, 2021, 02:06:08 AM
they're all Chevy after 1969, as far as I know.  I am not aware of any Pontiac 10-bolt applications after 1969.  I bet there is one, but I don't know what.
Title: Re: decode my 74 Trans Am rear end?
Post by: NOT A TA on December 19, 2021, 10:04:20 AM
they're all Chevy after 1969, as far as I know.  I am not aware of any Pontiac 10-bolt applications after 1969.  I bet there is one, but I don't know what.

'70 birds that didn't get 12 bolts came with 8.2" Pontiac 10 bolt rears.