Hello and thanks for any tips...

My 1983 has just gotten a "new" (but really used) instrument cluster which hoped to provide a working odometer. Sadly it does not work. But I did notice that the little R number under the speedo was different than the last unit I had (also a used instrument cluster in hopes of a working odometer - which also did not occur). If I recall correctly, one unit read "R 0.98" and the other "R 0.96" or such.

In driving home I compared the new unit's speed output with what my phone's GPS was indicating regarding my speed. At about 50mph on the GPS, the speedo unit was showing about 45mph. The difference was not always 5 mph. It seemed to vary a bit with slower speeds showing smaller differences.

I never performed this test with the last unit. Not sure why. Just didn't think about it.

My plan is to perform surgery on the unit I just removed (I think it is the one with the "R 0.98") and try to use some new gears to make the odometer work. If that succeeds, I may want to do the same on this newer unit. But I want to make sure I finally end up with the right unit calibrated for my car.

I have googled around a bit trying to find more info on the R numbers, what they mean, and how to get the right one for my car. Sadly, I have found nothing. So I hope someone here can clarify all this for me.

Thanks!