i need to know the formula to figure out which speedo gear i need. does anyone know this? i have a c6 8 teeth on speedo drive shaft. 4.10 gears, 27" tall tires. also where can i get the correct gear.
thanks
matt

 

The Ford dealer should have a book, and there or a junkyard are the only places to get the gears.

 

i checked with my local Ford dealer. they were absolutely useless. they said that all the gears were color coded, and that they did not know how many teeth each color had.they also said they had no way of knowing which gear i would need. snce the car i am working on never came with 4.10 gears. or any formula to find out which gear i needed. i know there is a formula. i used it on another vehicle. i just cat find it online anywhere.
thanks
matt

 

No surprise there.

The formula you want is:

Driven gear teeth = (Drive gear teeth x axle ratio x tire revs/mile)/1000

In your case that's:

driven gear teeth = (7 x 4.11 x tire revs/mile) / 1000.

or T = .02877 x tire revs/mile

You cannot accurately calculate tire revs/mile from diameter. You need to look it up for your tires either on the manufacturer's site or at www.tirerack.com