OK, I did a bunch of work on my '65 Skylark this winter, including pulling out the speedometer in an attempt to lube it (it was clicking). It has always read fairly accurately. When I started driving it this spring, the speedometer was slow all the time, regardless of speed. I figured I screwed something up and sent the speedometer out to get rebuilt. It came back with no click, but it's still 10 MPH slow. I didn't mess with anything else with the speedometer, but I checked the cable, wiped it off, and relubed it. I did get a new set of tires recently, of the same size, but I'm wondering if they could be that much larger to cause a difference. I would imagine, however, that it would be a certain percentage off at all times rather than roughly 10 off at any speed. Any ideas? I did email my speedo guy (who is from a very long standing business), so I'm waiting to hear from him, but I have a hard time believing that he wouldn't check the calibration before sending it out. What else might it be? Does anyone know where to get speedo driven gears for an ST300? Thanks, if nothing else, for letting me spitball here...this is a weird one. Sometimes, it's best not to poke the bear, that's for sure. I should have lived with a little clicking!
I believe the ST300 takes the same speedo DRIVEN gears as the THM350-400. You can get them. You need to know 3 things to figure out the calibration, rear tire size, rear gear ratio, and the number of teeth on the speedo DRIVE gear. Once you know those 3 things, it is a simple calculation to figure out the correct DRIVEN gear and see if it is available.
I just checked the odometer against highway markers and it's accurate. Now I really don't know what's wrong.
