Can someone school me on the mechanics of speedometers and fixes for common problems? I see basically how it works, but I know there is a lot more to this little instrument than I am aware of. I got have two speedo's for my 51 shoebox. -One bounces like a mother, half the time and doesn't work the other half of the time. -The other just bounces somewhat. Both are stock units. Also I have found that not all speedos are calibrated the same. For example you could use a ford or a chevy speedometer in the same car and get different speeds It's mainly curiosity. I'm just too stubborn to bring it to someone. I'de like to learn how to make it right myself. Do we have any speedo guys out there willing to share this info?
1. all speedometers (that i`m aware of) should indicate 60 M.P.H. when the speedo cable revolves at 1001 R.P.M. 2. to calibrate a speedometer you would need a test fixture with a cable that spins at 1001 R.P.M.( so that the speedo would indicate 60 M.P.H.) and an electro magnet that would induce magnetism into the hub or the fork ( i`m sure that there are technical names for these two parts, i just don`t know what they are). 3. bottom line is - if you have dis***embled the speedo to the point that the hub and the fork have been separated you need the services of a speedometer shop.
Usually when the needle bounces around it is the cable, not the unit itself. Unscrew the cable from the back of the head unit and pull out the inner cable. Check the inner cable for breaks and if it is OK, grease the lower half with wheel bearing grease and push it back into the outer cable. Turn it as you insert it to evenly spread the grease then screw it back onto the head unit.
Thanks for the tip. I didn't even think of the how smoothly the cable was turning. I thought maybe there was some spring that was supposed to keep the needle steady that was missing.
So there IS a magnet in there. I have not dis***embled anything, but with the speedo out of the dash, just about everything is in plain view. I had a feeling there was a magnet that spun in the center. Thanks for info about 1001 RPM = 60 mph. Everything appears to be there and working fine.
They also have a small hole that is plugged at the shaft. You can pry the plug out and put some three an one oil in the hole. Most time you can see some felt in the hole. After oiling replace the plug.
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