Repairing speedo drive in a Frank Sanderson single disc

[paulnobodyimportant]

Last summer, whilst trying to keep up with a Vespa GTS and me going flat out on a TS1, my speedo suddenly stopped. Anyway, its winter maintenance time and I have set about to solve the speedo issue. By a series of elimination, it seems that the speedo drive in the Frank Sanderson disc, see photo below, has packed up. How do I know? Well, I put a small piece of speedo cable into the disc drive and spun the wheel around, but the cable never moved, no matter how I wiggled it into the housing.
So the question is, as anyone else had the same issue and how to I repair it.
Failing that I will contact Frank.
Many Thanks

My disc


Photo from Lambretta Innovations web site

[soulsurfer]

It looks like your disc bolt is clouting the speedo drive
I think I have some spare drives for this that may do you for spares. Is there a part number or ratio on your drive?

[wack 63]

I could be wrong but you need a Vega drive as there are several versions of these drives with different ratios.Also you can twist the brass plug out of the body then the worm can be removed to check and I would suggest you check the spacer between the drive and hub bearing.