Question Ford Ford F1 guys

[RPW]

Has the 48-52 F-1 speedo (100mph) and the heavy truck (80mph) speedo the same internals?

I mean, is the different reading of the 80 mph Ford heavy truck speedo due to different internals of the speedo or is it the output from the gears in the gearbox that makes the 80 mph speedo to read different?

Why I’m asking? Well, I have a good working 80 mph speedo and a 160 kmh scale that I would like to use on the speedo (160 kmh is same as 100 mph).

 

[rotorwrench]

Magnetic drag cup type speedometers usually have similar internal parts if they are of the same make. A big truck had different rear axle ratios than a smaller light duty truck would have. The 80 MPH may have a different calibrating spring that acts on the needle to keep it from rotating along with the magnet. The spring pressure is adjustable to get the calibration within the range of operation. If you could find a speedo shop with one of the old calibration machines, they could tell you real quick if it could be used with a 100MPH dial face. If the needle has room to move farther, then it might work. You can tell a lot by the angle degree of relationship between the two dial number plates. If 80 MPH is in the same location as 100MPH on the other dial, you might have problems getting it to calibrate correctly through the rang of operation. If the 100 MPH mark appears to be a lot farther around the circumference of its dial than the 80 MPH unit, it might work OK. In other words, both dials should have 80 MPH in the same dial location.

Kerby