Posted by Chris Case [173.245.48.192] on Wednesday, June 28, 2017 at 10:18:08 :
Speedos themselves can be fine tuned, once you get the drive gear ratios right.
My guess is the spinning magnet is getting tired with age. They work by spinning a magnet near an aluminum part attached to the needle, aluminum is semi-magnetic. Plus the return spring gets tired.
Lube first.
Input rpms (cable) to mph is a standard. 100rpm = 50mph. (IIRC, it's been ten years, maybe 100=60mph?)
You'll need to figure out how fast a drill press or lathe goes. I used a tachy-meter and a stroboscope. But I bet there is an ap for that these days. My lathe does 84rpm, = 42 mph. Good spot for a PW to be best accuracy. Remove the speedo from it's can, hook up a cable from chuck to speedo, and dial it in. IIRC, You adjust the return spring on the needle.
While I was at it, I did every speedo on my parts shelf. Three, in about an hour. Including a metric one from the junkyard.
I used a GPS in the truck to check things out before changing gears, and also a Google directions for distance traveled vs odometer reading. Now a days, there is an ap for that, I borrowed a Tom-Tom.
Good luck, have fun, keep it safe. Spinning power tools do have their hazards. Just ask my fingers.
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