01-09-2020, 10:05 PM
What you need is a corrector box from someone like Speedograph Richfield. You need to know the turns per mile coming out of the speedo drive on the gearbox, and the turns per mile the speedo head needs. They do a set of gears which fastens to the back of the speedo. Costs about a hundred quid. Sounds a lot but it will be a lot more to have the speedo recalibrated properly.
Alan Fairless