Your description of the situation makes perfect sense. However, there is no answer like "turn the needle X degrees and press it onto the spindle". Positioning the orientation of the needle on the spindle is the first step in calibration. Google for the 27 page PDF document by Anthony Rhodes entitled "Repairing Jaeger and Smiths Speedometers". This is a must-have document for anyone attempting to repair or rebuild their own Smiths mechanical tachometer or speedometer.
The information below comes a bit late to you but it bears repeating since your gauge is not fully assembled yet. The odometer wheels and such need all the cleaning you describe and only a tiny trace of very thin oil on the shaft they are mounted on. Make sure all the dirt on the shaft and inside the number wheels is removed to minimize binding in the future. Do NOT oil the spindle that the gauge needle mounts on. Both the upper and lower supports for that spindle are needle bearings that are intended to run dry. Clean them thoroughly with alcohol but do not oil them when you are done.
You are going to have to get creative to restore the calibration to your speedometer... or you are going to have to send it off for professional calibration. I will outline below the basic steps I use. They may be of no use to you if you don't have access to various equipment.
Look on the face of the gauge for a 4-digit number near the odometer window (4 digits for MPH speedometers). That is the "turns-per-mile" (TPM) number. If you spin the speedometer cable counterclockwise at the RPM equivalent of the TPM number, the gauge will read 60 MPH. To calibrate the gauge you need a motor or machine that can run at a constant speed and drive a piece of broken speedometer cable or a nail sharpened into a square profile. With a broken piece of cable or sharpened nail attached to your motor and inserted into the back of the gauge, run the motor counterclockwise as viewed from the back of the gauge. With the drive motor turning a constant speed you position the gauge needle gently on the spindle at the appropriate speed (MPH). When you are satisfied you gently press the needle down on the spindle for a fraction of a second then immediately release pressure. If the needle is not where you want it, stop the motor, remove the needle, and try again. You may have to "lead" the MPH value by a few increments so the needle drops to where you need it to be. Once you have achieved accurate needle positioning for the motor speed, stop the motor and when the needle comes to rest at zero, press the needle more firmly onto the spindle.
As an example, lets say you have a speedometer where the TPM number is 1280. (That would be for a car with the 3.44 final drive and 10 tires/rims.) Now lets say you have some type of motor that can run at a constant 1000 RPM AND you know the speed is accurate. 1000 RPM /1280 TPM = 0.78125. That number (.78125) is the percentage of 60 MPH you would have when turning the cable at 1000 RPM. 60 MPH x 0.78125 = 46.875 MPH. Let's call that 47 MPH. So, if you drive the 1280 TPM speedometer at 1000 RPM you would position the needle at 47 MPH to restore the gauge calibration.
I have a small, variable speed, DC drive hobby lathe at home. I have outfitted it with a tachometer display so I can always know how fast it is running. When I am working on gauge calibrations I drive a bit of old speedometer cable held in the lathe chuck to operate the speedometer. This works quite well. Being a variable speed lathe I can set the calibration at 60 MPH and then confirm it is "close enough" across the real speed range I am concerned about (typically 20 MPH to 70 MPH).
You can see why if you don't have some equipment to improvise with you may want to send the gauge off for calibration.
EDIT: I see you are in Wisconsin. Over here there are a handful of highly regarded vendors who repair and calibrate Smiths gauges. If you decide not to try calibrating this yourself, look up Nisonger, Mo-Ma, APT (gaugeguys.com), and Palo Alto Speedometer. There are others who will calibrate the gauge for you but the firms I list above are the ones most people reference. Nisonger is in NY so they may be the closest to you.
Edited by dklawson, 31 December 2013 - 12:35 AM.
