Speedometer driven gear - number of teeth.

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Oldgearz

Senior Member
For whatever reason, my speedometer on my 54 customline reads about 6 mph higher than I'm going when in overdrive. I've never checked it in non-overdrive. I bought a 20 tooth speedometer cable driven gear to replace the existing 21 tooth gear. Before putting it on, can someone tell me if I'll make it better or worse using the 20 tooth gear. I have a 4.10 rear and book says I should use 7 tooth driver and 21 tooth driven. I can't count the driving gear because it appears to be a worm gear that I can only partially see with a mirror. What I do see looks like 6 teeth.
 
The speedometers tended to read a little high even when new. The odometer is gear driven and is more likely to be accurate than the tiny springs and spinning magnets that move the needle.
So check the odometer against GPS or mile markers first.

Less teeth on the driven gear will spin the speedometer faster.
 
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