# 66 differential question



## Al's 66 goat (Jul 21, 2021)

I've got a 66 goat 4 speed car .
Engine is about ready to go in .
What rear dif did they commonly put in these out of the box ?
What numbers on the rear end would I look for and where ?
Ultimately we'll probably take the cover off anyway but curious about what gm was putting in these cars for gears


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## GTOTIGR (May 3, 2020)

Hi Al,

Here’s some information that may be helpful.


http://www.wallaceracing.com/axledata2.htm




http://www.iegtoclub.com/Tech%20Lib/gto_axle_identification.htm



While the gearing range was broad, and depending on what you intended to do with the car, you could get differential gearing from 2:56 to 4:33. My cars are Muncie 4 speeds with 3:55 and 3:90 gears. I’ve also had 3:36 gears, both 3:36 and 3:55 are good all around gears. The 3:90 gears are fun around town.

Cheers


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## GTOTIGR (May 3, 2020)

BTW, if you have the PHS for your car it will tell you what deferential gearing your car was born with, if originality is important to you.


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## GTOJUNIOR (Aug 7, 2011)




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