A good guess would be that 80% or more of the speedometer issues involve this same scenario. Most often this occurs on 1963 and later speedometers that contain a trip odometer. Basically, the same parts that are used in this unit, are used in a speedometer with a total odometer only. The extra strain of the trip odometer can contribute to wear on the worm gears that drive the odometers. A quick fix would be the replacement of the second worm gear. It's just that: a quick fix. This will only provide a temporary resolution because wear also occurs on the first worm or magnet which drives the second worm. The correct fix requires rebuilding and/or replacement of the entire frame assembly. This requires special tools and equipment and cannot be performed without them. We have the necessary equipment to perform this job properly.