OK, I have now finished with the gear swap in my '62 C10. Speedometer is way off. How do I calculate what new gear I need to correct it?
I have the SM420 4Speed, 3.38:1 rear end, and P275/60R15 tires (28" diameter).
When I had the 3.90:1 gears, my factory speedometer was fairly accurate. Now it reads very low.
I've looked at a lot of online calculators, but they all ask what the number of drive teeth are. I don't know what they are for the SM420. Was there a standard drive gear in the SM420?
