Sometimes it is pretty hard to tell if the gear is good.
I had one odo that wouldn't work because of a slip somewhere else.
I caught it in the act by chucking a headless nail in my electric
drill and using the square point to drive the speedo/odo while I held
it in my hand. (had to run the drill backwards).

I had bought a new gear at $25 and once I got it into a functional odo,
it works great.
--
George Downs Bartlesville, Heart of the USA!