I suggest that you take the speedometer cover off and see if one or more of the internal shaft bushings has fallen out. If so, it will be captured inside the case so it won't be lost. When the odometer wheels stop turning and the speedometer still functions, that is what generally occurs. The loose bushings can easily be re-installed. I have used a very small amount of model airplane thick "CA" glue to retain the bushing after cleaning with thinner. Lubricate the mechanism while you have it apart. Gar Williams