speedometer driven gear
 

i have a 66 stang with a c-4 tranny and a 2.80 gear ratio. can anyone tell me what color driven gear i need for my speedometer cable and how many teeth it should have? no one else seems to be able to help. the tranny is out of a 67 cougar if that makes a difference. the driven gear i have on it now is out of my old 66 c-4 tranny but it is reading about 8-10 mph to fast.

You need to count the number of teeth on the driven gear that you are using now and find one with at least 2 less teeth. Might take 3 or 4 less, kind of a trial & error thing. I have a box of gears from over the years, try one and check it against the mile markers on the interstate. Lower numerically gears = less teeth on the driven gear. Hope I haven't thoroughly confused you.

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67 428 fastback
88 GT

You can calculate the needed speedo gear teeth with the formula below.

speedo gear Teeth=Drive Gear Teeth (Times) Axle Ratio (Times) Tire Rev. Per Mile Divided By 1000

The drive gear teeth number on a 65/66 C4 is 7, if the cougar you took the trans out of had tall gears it might have a 6 spline tailshaft (6 drive gear teeth).

-JON