My speedometer has suddenly started reading about 3 times the correct speed. At about 60mph the needle manages to go full circle and hits the buffer in the dial. I was wondering if this is an earthing- or some other electrical-problem. The speedo cable was replaced about 20k miles ago. Any clues at all, very much appreciated. Ta, bogbasic.

Thought they are mechanical drive from N/S bearing.

yep, this has something to do with the speedo unit itself

this is the best time to record a highspeed 0-60 or 0-100 movie though