12 Bolt Rear End ID Help Please

[72 Cheyenne K20]

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]

TAM is the ratio code, which is 2.73

[72 Cheyenne K20]

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]

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]

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]

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

[72 Cheyenne K20]

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]

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]

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!