Speedometer Won't Zero

[Jwawhite]

My speedometer will not return to zero mph unless I travel in reverse for a bit.

Any suggestions?

 

[KULTULZ]

If it zeros in reverse, most likely the speedometer head needs cleaning and lubrication.

 

[rotorwrench]

The old Ford units last relatively well over long periods of time but all of them need some lubrication now and then. Some have a tiny plug near the drive input that can be removed to apply a light oil to the wick inside but it is mostly for the magnet drive bearings. The magnetic drag cup bearings generally just need to be clean and free of corrosion or other contaminants. Not all speedometers are made the same so I can't give you much more information than that. The drag cup clock spring can eventually lose some of its tension but is usually adjustable for unit calibration.

The drag cup is connected to the needle and the magnet that is connected to the drive runs inside of the drag cup so the two assemblies have different bearings. If the magnet shaft bearing wear too much, the drag cup will eventually stick to the magnet. It makes a hell of a racket and generally ruins the clock spring that returns the needle to zero when that happens.

 

[papanick]

Yes it will need to be serviced and cleaned.