The 1976 T140V’s speedometer was fluctuation about 30 mph and was reading 40 mph high. I checked the condition of the speedometer cable system and it was good. I re-lubed that part of the speedometer system. I found when the speedometer input was rotated slowly by hand it would the needle would immediately rotate to 30 mph and fluctuate. Armed with a couple of helpful articles on Smith’s Speedometers I opened up the speedometer head. I found the input magnet had a loose retaining plate rivet and allowing the rotating magnet disc to rub the aluminum needle disc. That seems to be the source of the fluctuation and the instrument reading high. I inspected cleaned and lube all rotating parts with a very light tool oil. I reassemble the input drive and replaced the four retaining rivets for the input drive retaining plate and odometer retaining plate with screws for future disassemble. The bike has stock tire size and final sprocket sizes. I located a formula to calculate rpm gauge reading to MPH in 5[SUP]th[/SUP] gear to calibrate the speedometer. Tomorrow afternoon I will try to calibrate the speedometer to indicate the proper mph. Just for good measure I will further test it against the family car.