dale Posted July 20, 2018 Report Share Posted July 20, 2018 Is it possible to fine tune the speedometer at the speedometer head ? Quote Link to comment Share on other sites More sharing options...
greg g Posted July 21, 2018 Report Share Posted July 21, 2018 Not for speed errors. There is a tunable thing a majig that you can mount the speedo cable to. Don't know if its externally adjustable or you need to mess with gear sets. Quote Link to comment Share on other sites More sharing options...
dale Posted July 21, 2018 Author Report Share Posted July 21, 2018 THX.. Ill check it out. Quote Link to comment Share on other sites More sharing options...
dpollo Posted July 21, 2018 Report Share Posted July 21, 2018 there is an adjustment at the speedo head but it needs a tech who knows what he is doing and a test bench. Quote Link to comment Share on other sites More sharing options...
TodFitch Posted July 21, 2018 Report Share Posted July 21, 2018 2 minutes ago, dpollo said: there is an adjustment at the speedo head but it needs a tech who knows what he is doing and a test bench. I assume "fine tune" means the odometer is okay but the speed is off. . . In my youth I attempted to adjust the speedometer in my Plymouth and ended up breaking more than I fixed. I finally took it to an old time automotive instrument shop to have the damage I did repaired. I think I could do better now as I am more inclined to study things more rather than bull ahead. But those are fairly delicate instruments that are easy to break. And it would take a bit of thought and work to setup a workbench where you could calibrate it. End result, I concur with dpollo on this. If I assume wrong and the odometer is off, that implies someone changed out some gears somewhere or changed the wheel/tire diameter and then greg g's suggestion of a correction gear box added to the cable might be appropriate. Quote Link to comment Share on other sites More sharing options...
DonaldSmith Posted July 21, 2018 Report Share Posted July 21, 2018 I had my speedometer rebuilt several year ago. The shop spun the speedometer at a set RPM, and adjusted the mechanism accordingly. (Fascinating place. The father had accumulated a vast collection of model trucks, cars, petroliana, etc., that lined the walls of the shop. The son was chafing under the father's tutelage; couldn't do anything right, per the old man. Obscenities traded. ) The other half of speedometer correction is the speedo gear in the transmission, which has to be correct for rear axle ratio, tire diameter, etc. My rebuilt speedometer was about 10 percent off. I happened to score a ratio adapter on line that was just right. Now, the speedometer is off at higher speeds (according to the Garmin) so the speedometer must be getting tired. (I wonder if the speedo shop is still in business. But I don't feel like taking the speedometer out again.) Police departments would have their speedometers calibrated periodically, and the ratio adapters came with complete kits of gears, to make any required correction. Now I guess everything is electronic. Quote Link to comment Share on other sites More sharing options...
mrwrstory Posted July 21, 2018 Report Share Posted July 21, 2018 What causes your speedo to be in error?....new rearend?....diff. tire dia?....diff. trans?....speedo need to be refreshed?.....how great is the error. I have a modified P-15, stock speedo, diff. engine, diff. trans, diff. rearend. I bought the little transducer you see advertised in several auto publications. Told the supplier the diff. between indicated speed and actual speed (via GPS). He customized the unit and it's spot on for less than $100.00. If you need the source let me know and I will dig through my receipts. Quote Link to comment Share on other sites More sharing options...
Eneto-55 Posted July 21, 2018 Report Share Posted July 21, 2018 I have heard that there is a GPS device available that connects to the speedometer cable, and gives a correct reading on any mechanical speedometer. But I would think that it would very possibly still be necessary to calibrate the speedometer to match distance & speed correctly. Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted July 23, 2018 Report Share Posted July 23, 2018 Ok so what is the real issue with the speeomtere or the odometer? If the spped dial is not showing the correct MPH then use a gps devise and run it on the GPS battery and run down the road. The GPS will tell you the exact speed you are going and then you can callibrate the difference between the two unit so Lets say the GPS state that you are going 40 but your speedometer show 35 so you would know that the speeomter is 5 MPH under your true speed. So try this with differnet speeds while drivng and then you will have a better idea of your issue. So are you trying to go faster then you want to with these old cars I thought the idea of having an antique car was for us to slow down allitle and enjoy the driving and not be in a big hurry and always rushing to get somewhere. Just my 25Cents worth of input. Rich Hartung desoto1939@aol.com Quote Link to comment Share on other sites More sharing options...
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