Author Topic: decode my 74 Trans Am rear end?  (Read 353 times)

SP Steve

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decode my 74 Trans Am rear end?
« 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.

Maxthe222

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Re: decode my 74 Trans Am rear end?
« Reply #1 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.
1987 T/A GTA L98
1979 T/A Y84 WS6
1979 F/A W72 WS6
1978 T/A L80 WS6
1978 Formula L80 W50
1971 Formula 400 4-Speed

SP Steve

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Re: decode my 74 Trans Am rear end?
« Reply #2 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.

roadking77

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Re: decode my 74 Trans Am rear end?
« Reply #3 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.
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Maxthe222

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Re: decode my 74 Trans Am rear end?
« Reply #4 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.
1987 T/A GTA L98
1979 T/A Y84 WS6
1979 F/A W72 WS6
1978 T/A L80 WS6
1978 Formula L80 W50
1971 Formula 400 4-Speed

Re: decode my 74 Trans Am rear end?
« Reply #4 on: December 18, 2021, 10:06:47 PM »

firebirdparts

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Re: decode my 74 Trans Am rear end?
« Reply #5 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.
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NOT A TA

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Re: decode my 74 Trans Am rear end?
« Reply #6 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.
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Re: decode my 74 Trans Am rear end?
« Reply #6 on: December 19, 2021, 10:04:20 AM »
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