Speedo Bench Test

Is there any way to bench test a speedo from a 71 Satellite? When I drive it bounces wildly, and the odometer doesn't work. I've got the car torn down now, and the console sitting on the bench. I've got another speedo from a 71 RR, but I have no idea if that one is good either. Thanks.

speedo cable and a drill.

I took one apart expecting to find a sticking cable. Turns out something in the speedo head was bad, and that was making it jump around. I mounted one of the square bits in a drill to test just the speedo.

Once you get them out it should become apparent where the problem is.

I've cured many speedometer related issues simply by greasing the cable. I always like to use a high quality wheel bearing grease.

If the odometer is not working, then I would suspect further issues in the speedometer itself.

Thanks. Hopefully between the two of them one will work.