VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 AC speedometer calibration

My 1928 speedometer was rebuilt, the Odometer is dead on however the speedometer reads 5 to 10 MPH slow. How are these adjusted? Do you have to move the horseshoe magnet or is there an adjustment screw or some other way to do this?

-Tyler

There is an adjustment on the spring on the speed indicating drum. Should probably be adjusted by a speedometer technician.

Trial and error works too and you don't need a technician for that, just someone driving behind you to check your speed or you could simply use an app on your phone to find your actual speed. I found that the magnets tend to lose their magnetism. Adding a little magnet to each pole helps if you run out of adjustment.

Thanks for the responses. I had played around with the spring adjustment a bit, if I loosened the tension all the way it would read a couple mph closer to true but the drum would also bounce around. I know Bob's Speedometer had it calibrated on the bench but I'm not sure if they ended up re-magnetizing the horseshoe magnet or not. My guess is the magnet is a bit weak and the steel dash and electrical wiring near the speedometer in the truck is enough to throw it off.

I think I'll leave it alone, juice just not worth the squeeze :-p

-Tyler