Posting this in case anyone else experiences the same problem. Inside the speedo unit is a worm gear which drives a small plastic gear that operates a lever to increment the odometer with every revolution.
This gear can develop a hairline crack which widens the gap between the teeth either side of the crack. The result is that the leading edge of the worm gear thread hits the tooth of the plastic gear rather than slotting nicely into the gap between the teeth - this happens once a revolution of the plastic gear.
I fixed mine by cleaning out the crack with a solvent, then inserting some acrylocyanate glue and squeezing the gear together with tweezers. Once set I cleared out excess glue then shaved off the corner of the tooth so the work gear could engage with it cleanly.
I am having the same issue. Actually, I "was" having the same issue and now it has just stopped working in general.
Was debating on a whole new gear, but at almost $200 and I am not 100 % sure its not something deeper.
Will your glue fix be obvious when I pull it all apart?
I have had mine apart before, I cleaned it up. It spun somewhat smooth, but not perfect at all. Put it back in and no go. Clicked for a bit and then stopped working.
Since I may have to do mine, I can try to take pics and post and hopefully help others with this prob
As said the larger gear that is driven by the worm drive splits, which makes it hop (till it breaks). There are different sizes (colours) based on the calibration etc. They are readily available as the system is used in many British motors (Smith or something). I know this because I changed mine 2 years ago and I recall the same gear was used in a Rolls Royce!