speedometer calibration
10-15-2012, 10:33 PM
#1
Racer
Thread Starter
speedometer calibration
i have a few speedometers for my 69. none of them read correctly over the entire range of the speedometer. i am in the process of learning how to bench calibrate them.
i have found that if i use a timer and the odometer i can set the rpm of my lathe to match the time it should take to run a mile on the odometer at a given speed. i then adjust the cross bar in the picture below so that the needle reads correctly at several speeds. it takes a few tries going back and forth between different speeds, but i am able to get the needle speed to match the time it takes to do a mile at the speed the needle shows.
question is,
is it really that simple?
[IMG]
[/IMG]
i have found that if i use a timer and the odometer i can set the rpm of my lathe to match the time it should take to run a mile on the odometer at a given speed. i then adjust the cross bar in the picture below so that the needle reads correctly at several speeds. it takes a few tries going back and forth between different speeds, but i am able to get the needle speed to match the time it takes to do a mile at the speed the needle shows.
question is,
is it really that simple?
[IMG]
Last edited by oldboat; 10-16-2012 at 01:14 AM. Reason: addition
10-16-2012, 09:06 AM
#2
Race Director
Yes, that's all there's to it as long as you were able to make it show correct at multiple speeds.
You may want to look into an optical tach. You put some reflective tape on the chuck and it will show you the rpm. I got one for $35 and it works fine.
Sounds like you got lucky with your speedos. On mine the magnet was too weak and it read low even with the adjustment all the way loose. I added some neodymium magnets to make it strong again. The factory used a big electro magnet to magnetize it, but since I don't have one I improvised.
You may want to look into an optical tach. You put some reflective tape on the chuck and it will show you the rpm. I got one for $35 and it works fine.
Sounds like you got lucky with your speedos. On mine the magnet was too weak and it read low even with the adjustment all the way loose. I added some neodymium magnets to make it strong again. The factory used a big electro magnet to magnetize it, but since I don't have one I improvised.