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Need to know how many teeth are on the "drive shaft" that meshes with the speed ometer gear on my C6. I guess the vary...so I need some help here
1973 Mach 1 Mustang. Had a 351 4v if makes any differance. Factory gears were 3.25. Thanks a lot guys! I guess we can VOID my last post on it.

Jeff Given
 

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If you start with a 3.25 rear and go to a 4.11 rear you add 26% to the rear ration.
I would think you need to add 26% to the teeth on the gear that matches the 3.25 rear.
ie if it is an 18 tooth gear go to a 22 or 23 tooth gear.

I may be wrong but it sounds like the right maths.
 

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I'm not sure how right Tony is with his formula, but so much changes. Was the thing right in the first place? stock tires?

Go down to a speedometer shop, if they arnt to buisy you could be out in 15 minutes. They will put it on the rollers, get a reading, then change the gear, while you wait. I worked at a speedo shop 18 yrs ago, I would imagine not that much has changed.

either way you have to have it checked. they will have an assortment of gears. Don't waist your time trying to do it your self.
 
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