I recently purchased a 1958 F100 with a 1970 351C and C6 trans. I installed a speedometer cable in place of the broken one. The speedometer works well but is reading about 20 mph too fast (80) at approx 60 mph. The current gear is 16 tooth blue/green plastic and is about 2 inches long. I ordered a replacement 20 gear black plastic gear and it is only approx. 1 inch long. It does not work, the gear seems not to make contact. Any ideas? Thanks

 

Not sure what gear ratio on mine is but mine is about 5 mph off and mine is an orangish color. Someone will post soon with a better answer

 

sounds like the gear isn't seated completely..

the contact point is up high on the gear, close to the cable.

Sam

 

The correct 20T driven speedo gear is: C8SZ-17271-B / Orange / Available from Ford / MSRP: $3.75 // FTE sponsor PARTSGUYED.COM price: $2.70.

IMO, a 20T gear is one tooth too many for a speedo that is reading 20 MPH fast.

C7VY-17271-A .. 19T Driven Speedo Gear / Tan / Available from Ford / MSRP: $2.98 // PARTSGUYED.COM price: $2.15.

 

here's a good calculator

Speedometer Gear Calculator

Sam