Because on an inaccurate speedo in my 64 Fairlane and 56 Bird, I experimented with different driven gears using my GPS. Each tooth difference accounts for about 5 MPH at around 60MPH.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

I need one too since I put a T-85 overdrive in my '56. Tee-bird products has some I think. I got my cable & housing there. I'm going to try a 23. Mine is 10 mph off. If you google "speedometer gear" there are dozens of places that come up....


Doing Fords for 45 years. '56 Customline Victoria

E.J. in Havana FL

I thought most old cars had optimistic speedos. Mine reads about 8% high against a GPS. I didn't think odometers could run backwards. Easy test, drive backwards for a couple of hundred feet and see if it moves.

Ian:

The older mechanical odometers will run backwards. An old used car lot trick was to hook an electric drill to an old piece of cable core and remove some of the mileage from the odometer. The new electric odometers read "forward" regardless of direction of rotation as they read magnetic pulses.

John - "The Hoosier Hurricane"