[Andre]

I didn't see this before, but lubricating the cable is the way to go. Ill bet your cable sheath has a bad spot and has let dirt get in and cake things up. Id remove cable and sheath, remove cable and inspect for damage. Clean inside of sheath to remove old grease and dirt. Relube generously and reinstall. If that fails, the speedometer head has gotten gunked up. On my 64 droptop the speedometer literally warms up, although the odometer works fine. That means my speedo has gone bad and must be replaced.