Are switching speedo gears the only reliable way to adjust an inaccurate speedo?
I'll use the calculator chart above to get an estimate of what teeth count I need with 225/70-14 tires and a 2.76 rear.. then compare to the current speedo gear in the car..
The speedo in our '65 with cable-shift 727 automatic is off by about 10% too fast (reads 90mph when actual is more like 80).
So if I count the teeth on the current speedo cable gear, I figure I have to find a replacement with 10% fewer teeth. is that how this works?
Thanks,
- Art
That chart is not accurate for the 65 style speedometer pinions.
Conversion to modern tire sizesSnipped from the 65 Plymouth FSM
Looks like you need a 17 Orange pinion, assuming you don;t already have that. The coverage spread is kind of wide. Brewer's has used, $80.