So I finally have a working speedometer and odometer after piecing one together from 3 different speedo heads. My speedo is off but that isn't an issue as I had the needle off plenty of times and just haven't got it positioned correctly. The problem is for every 20 miles travelled my odometer reads 19. The odometer works separately from the speedo on these Denso heads. It's not a big deal but I've invested several full days in this so I might as well continue to refine it. I've been checking it with a GPS speedometer app.
Truck has a 37 tooth speedo gear, so does anyone know how much 1 tooth will change the odometer? I have a 35 tooth gear but not a 36. I'd like to do this once and set the speedo needle if possible.
Thanks for any help.