I knew my speedometer was off, seemed I was traveling faster than it showed. Finally checked it with a gps app and shows it is progressively off. at 25 I am really traveling 31, at 45 , I am traveling around 55-56. Wish it was accurate but on the other hand I like that my ole truck goes down the road at 55 and not terribly wound up .
Assuming that it's a cable driven speedo... Try a drive gear with one less tooth. Or more easily, try a driven gear with maybe two more teeth. Also assuming that such parts exist and not knowing what trans you have or which drive and driven gears are currently in place.
That's a 19% error and needs to be corrected on the transmission end with the speedometer driven gear or gear rario adapter. If you let me know what transmission you are running and how many teeth on the speedometer driven gear I can help you to get it corrected or at least closer. 19% may be to much to correct with a gear change it may need a ratio adapter which I can make up for you.
My truck ( 39 ford) has the standard 3 speed top loader , I knew the # stamped on casting but will have to look again . seems it was 78-7008 or something like that.
If its the standard 3 speed with the metal speedometer gear the only way to correct the calibration would be with a ratio adapter.
Those radar speed things on the side of the road tell me I am going 45 when the speedometer says 75 and 65 when the speedo says 100. I will fix it when I get to it, meanwhile I know my actual speed by looking at the speedometer
Have installed various ratio adapters with great success as e1957v says. Sometimes can easily be corrected with driven gear if not too far off.
Driving my 48 Ford to breakfast with the guys one morning with a friend in his 49 Olds side by side on the Highway, I pointed at the Speedo and he nodded his head . when we arrived @ the Café , I asked him " How fast were we driving ? " he said " About 150 " so his speedo was not correct either . I installed an electric unit from Speed Hut and dialed it in with the GPS on my son's phone. all better now
"Those radar speed things on the side of the road tell me I am going 45 when the speedometer says 75 and 65 when the speedo says 100. I will fix it when I get to it, meanwhile I know my actual speed by looking at the speedometer" It's reading in kilometers. Perfect for when you travel to Canada.
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