The cable cannot hold the needle from returning to 0
The cable only drives the magnet
When the cable stops the needle drops to 0 with the clock spring
The spring might have some oil/dust on it or the needle is rubbing the glass or the tiny bearings that the needle cup rides on are too stiff
But the speedometer will have to come apart either way because it should be impossible to hold the needle from the outside of the unit, there is a problem inside the speedometer.
-s
