[Vwdiesel] Speedometer issue

[Caleb Van Dyke]

Does anyone know if there are different gears that drive the speedometer on a 1981 Rabbit diesel pick-up? I changed the transmission from a 4-speed to a 5-speed (code F0) and also upped the rim and tires from 13's to 14's keeping about the same height (as I had 185/75/13, now I have 185/70/14). Now my speedometer appears to be reading a bit low, but I have yet to figure out how much. I believe I can go out on the freeway and see if it matches mile markers, but if it's off how do I calculate the error? Also, if I need a different speedo drive gear, where might I purchase one?

Caleb