Replaced the 17 teeth driven gear todayon my 66 coupe to one with 20 teeth and the speedometer is now pretty much accurate in terms of mph and mileage calibration. Another problem solved with the help of this forum!!!! Thanks!!!

 

Thanks for reporting back to us.

 

Was your firewall grommet in good shape?

I can’t find one and was thinking of using a 65-66 accelerator grommet.