Well I just reread this whole thread and I still didn't see any definitive instruction on the calibration of the needle. From my vantage point, that needle has to go back on the shaft in exactly the same rotation or the Speedo is going to be off. The only way that it can be properly calibrated is to check it against a known standard and rotate the needle on the shaft till it is in calibration with the dial face.
I’m still mulling over what Fred posted about comparing the speed over distance registered by the odometer, and then doing the math. That sounds like it would work but I’m not sure to what degree of accuracy would come of it. Seems to me that you would have to be able have pretty tight control over the speed that you register to make that work.
The magnet pulls the speedcup, which is biased by a hairspring. The distance the magnet is from the speedcup (determines the slippage) and can effect the calibration but this is pretty much fixed. So that leaves us with the bias adjustment which can cause it to read slow or fast. By winding it tighter by tuning the needle shaft the Speedo would read slow, by not winding it tight enough it would read fast. So this brings us back to the only adjustment that we can do, which is the rotation of the needle on the shaft. So like the calibration of the arms on an analog clock, the needles have to be friction tight and free enough that you can turn them slightly.
It would be interesting to hear how they are checked from someone who works in a real calibration shop.
Also, I haven’t heard from anyone else that has found a taper on the shaft, or was the one in Frank50’s speedo the only one????
Denny Graham
Sandwich, IL
