12 Bolt Rear End ID Help Please - The 1947 - Present Chevrolet & GMC Truck Message Board Network

72 Cheyenne K20 · 09-19-2022, 07:53 PM

Hi All,

Can anyone please give me gear ration info on my 12 bolt rear end. Have a 1980 Jimmy and the stamped ID from the top of the right tube is:

T A M 058W02

From what I was able to find out: the 058 is February 27th, the W is Warren & the 02 is the Shift. Please correct me if I'm wrong. I just can't seem to find the gear ratio anywhere!

Thanks, Scott

**MJN** · 09-20-2022, 09:11 AM

TAM is the ratio code, which is 2.73

72 Cheyenne K20 · 09-20-2022, 10:43 AM

Thank you very much for that info MJN!! 2.73 ratio, that’s why she’s a little sluggish off the line. Good highway gears though!

Scott

**mongocanfly** · 09-20-2022, 11:19 AM

My 86 had 2.73s.. with my manual L+3spd, I had to use L to get rolling.. would almost choke down starting in 1st

72 Cheyenne K20 · 09-20-2022, 05:55 PM

I've been on the other end of the ratio spectrum too. Had a 71 K20 I bought from a guy in Montana. 350 & a 4sp with I believe 4.56's. I was scared to get over 50 mph because the engine just screamed. I'd much rather be on this end!

I do have one more question. The front differential is a GM 10 Bolt. Any stamping I can look for on that? I did look for a ratio tag mounted to the cover, but no such luck.

Scott

**kwmech** · 09-20-2022, 07:02 PM

Should be thee same ratio as the front--in fact it better be

72 Cheyenne K20 · 09-20-2022, 08:50 PM

I'm positive they are the same ratio, tore up some snow last winter. I just wanted to know if there was a ratio code or a date stamp on the front axle & where that would be located.

Thanks Scott

**MJN** · 09-20-2022, 08:53 PM

front axles are stamped on the tube, similar to the rear axle. Heres a screenshot out of the 1979-1984 parts catalog, you can download a pdf copy from board member Hatzie and look up the code on yours.
http://67-72chevytrucks.com/vboard/s...d.php?t=545416

72 Cheyenne K20 · 09-20-2022, 09:19 PM

Well that's about the best piece of info I've received in a long time MJN. Downloaded and now able to not feel stoopid! I'll find time to dig through the gunk tomorrow and find the code.

I have to now, looked at 1980 front axle ratios available and 2.73 was not an option from what the book says!

09-19-2022, 07:53 PM	#1
72 Cheyenne K20 Registered User Join Date: Feb 2003 Location: Staunton, Virginia Posts: 554	12 Bolt Rear End ID Help Please Hi All, Can anyone please give me gear ration info on my 12 bolt rear end. Have a 1980 Jimmy and the stamped ID from the top of the right tube is: T A M 058W02 From what I was able to find out: the 058 is February 27th, the W is Warren & the 02 is the Shift. Please correct me if I'm wrong. I just can't seem to find the gear ratio anywhere! Thanks, Scott

09-20-2022, 09:11 AM	#2
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,051	Re: 12 Bolt Rear End ID Help Please TAM is the ratio code, which is 2.73 Attached Images __________________ '51 South Bend Model "9A" '56 Chevy 3600 NAPCO '74 Chevy Cheyenne Super K20-restored on 37's '72 GMC Sierra Custom K2500- in progress '08 GMC Envoy Denali '12 GMC Sierra 2500HD Denali '17 GMC Yukon XL VCCA member #58596 http://www.nohrco.com

09-20-2022, 10:43 AM	#3
72 Cheyenne K20 Registered User Join Date: Feb 2003 Location: Staunton, Virginia Posts: 554	Re: 12 Bolt Rear End ID Help Please Thank you very much for that info MJN!! 2.73 ratio, that’s why she’s a little sluggish off the line. Good highway gears though! Scott

09-20-2022, 11:19 AM	#4
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,671	Re: 12 Bolt Rear End ID Help Please My 86 had 2.73s.. with my manual L+3spd, I had to use L to get rolling.. would almost choke down starting in 1st __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

09-20-2022, 05:55 PM	#5
72 Cheyenne K20 Registered User Join Date: Feb 2003 Location: Staunton, Virginia Posts: 554	Re: 12 Bolt Rear End ID Help Please I've been on the other end of the ratio spectrum too. Had a 71 K20 I bought from a guy in Montana. 350 & a 4sp with I believe 4.56's. I was scared to get over 50 mph because the engine just screamed. I'd much rather be on this end! I do have one more question. The front differential is a GM 10 Bolt. Any stamping I can look for on that? I did look for a ratio tag mounted to the cover, but no such luck. Scott

09-20-2022, 07:02 PM	#6
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,635	Re: 12 Bolt Rear End ID Help Please Should be thee same ratio as the front--in fact it better be

09-20-2022, 08:50 PM	#7
72 Cheyenne K20 Registered User Join Date: Feb 2003 Location: Staunton, Virginia Posts: 554	Re: 12 Bolt Rear End ID Help Please I'm positive they are the same ratio, tore up some snow last winter. I just wanted to know if there was a ratio code or a date stamp on the front axle & where that would be located. Thanks Scott

09-20-2022, 08:53 PM	#8
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,051	Re: 12 Bolt Rear End ID Help Please front axles are stamped on the tube, similar to the rear axle. Heres a screenshot out of the 1979-1984 parts catalog, you can download a pdf copy from board member Hatzie and look up the code on yours. http://67-72chevytrucks.com/vboard/s...d.php?t=545416 Attached Images __________________ '51 South Bend Model "9A" '56 Chevy 3600 NAPCO '74 Chevy Cheyenne Super K20-restored on 37's '72 GMC Sierra Custom K2500- in progress '08 GMC Envoy Denali '12 GMC Sierra 2500HD Denali '17 GMC Yukon XL VCCA member #58596 http://www.nohrco.com

09-20-2022, 09:19 PM	#9
72 Cheyenne K20 Registered User Join Date: Feb 2003 Location: Staunton, Virginia Posts: 554	Re: 12 Bolt Rear End ID Help Please Well that's about the best piece of info I've received in a long time MJN. Downloaded and now able to not feel stoopid! I'll find time to dig through the gunk tomorrow and find the code. I have to now, looked at 1980 front axle ratios available and 2.73 was not an option from what the book says!



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