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Old 03-11-2009, 03:34 PM
fosterdl fosterdl is offline
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Differential Gear Calculations

I should be able to figure this out and it's most likely been hammered to death on this site, but, what is the equation to figure out what gears you need to correct your speedometer? OK, rear differential gears. I have a 65 Impala SS that came factory with a 6/three-on-the-tree. Since then it's been upgraded (?) to a 350/Saginaw 4 speed. Now I'm going to a 396 (correct block #) and a TH400. But I think none of that matters. It has 3:21(?) gears in it now and the speedometer is WAY off.(slow) It has a 10 bolt rear that I'm considering rebuilding with new axles and HD ring and pinion (Richmond) and I would like to know how to figure out what gears to use for correct speedometer readings. This will be for street use only, so I'm pretty sure the 10 bolt will be tough enough.

Last edited by fosterdl; 03-11-2009 at 03:50 PM.
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