Thanks Tim & Eric for the info.
Other than the face plate, the 80 & 90 MPM speedometer are identical. The 80 has high beam on the top, 90 has it on the bottom.
The guts, gears and everything else looks to be the same.
The speedometer needle is spring loaded and is driven by a magnetic field. There is an adjustment for the spring. Is the adjustment the only difference between an 80 & 90? There was about 1/4" difference in the setting between the 80 MPH & 90 MPH.
I would like to test the speedometer and calibrate it before I put it in.
Using RPM's in high gear (3rd) how fast, MPH is the speedo going.
Does 2000 RPM = 55 MPH or 1500 RPM = 40 MPH ???
Wheel/tire size is not a factor because the truck is off the ground.
