I "calibrated" mine using a electric drill motor. I had the speedometer out for a cleaning and new decals, so I figured it was a good time to check it. I have a hand held, mechanical rpm gauge I used to set the drill rpm with. Most all speedometers were set to run 1000 rpm (cable revolutions) at 60 miles per hour. I set the drill to run a 1000 rpm and set the throttle stop to always come back to that speed. I then installed the speedometer and ran it for 10 miles watching the odometer. Since the odometer is a direct gear to gear, it will read accurately to what ever rpm it is being run at. Once I did a minute rpm adjustment to get 10 miles in 10 minutes, I then started looking at the speedometer needle. It took a couple of tries, but all I did was remove the needle and reposition it till it read 60 miles per hour with the drill running at 1 mile per minute. At every other speed, the needle is slightly off, and the faster it goes, the slower it reads. 60 is where most of my driving is anyway. At slower speeds like 35, it's relatively close and I can judge from other cars how fast I am driving.
When I put it back into the dash, all I needed was a simple transmission gear change to get the odometer correct. Knowing the speedometer head was reading right, changing the trans gears was really simple. Now it tracks right with the highway markers.
It's not a true calibration, only a shop with special magnetic tools and new springs can do that, but for the DIY'er, it worked really good.
If you decide to try this, be sure to have the drill and speedometer setting at the same angle as the dash. The weight of the needle will change the reading.
Joe
Last edited by Joe H; 04/01/2016 2:26 PM.
