| Jone | -- 09-02-2015 @ 10:13 AM |
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While out for a drive in my 47 Merc today I happened upon a Sheriff's department mobile radar display. I went thru it at 50 mph, according to my speedometer, and the radar showed 55 mph. Is there a way to adjust the speedometer to make it more accurate? The car is an early 47, the speedometer has a trip odometer. I do not know if the transmission is original or not.
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| ken ct. | -- 09-02-2015 @ 1:30 PM |
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you can go up or down 1 tooth on the turtle unit to make more accurate reading. You would need to go less 1 tooth on the turtle to lower speed. If im wrong on that someone will chime in to correct me LOL. ken ct.
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| len47merc | -- 09-02-2015 @ 3:14 PM |
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Jone - I too have an early '47 Merc, my speedo performs the same and has the trip odometer. Given I am running taller tires (Firestone 710s) than originally came on the car I expect it to perform this way and validate actual speed with a GPS speedo app on my smart phone. Same results as yours - ~10% slow throughout the speed readings. When I change to original-height tires the speedo is very close to actual. Doubt your speedo is as inaccurate as you may think, but if you wish to change it to more accurately reflect your actual speed you have that option. If you change tire size in the future you will have to adjust again if it continues to be a problem for you. I have chosen to live with it and mentally adjust actual speed based on the 10% value - it comes naturally now. I also know a speedometer reading of 55 mph (my max cruising speed by choice) equals ~60 mph actual and 2,500 rpm - the Ford-designed optimum rpm for 59AB torque. Given the 2,500 rpm at 60 mph actual result I will stay with the 710s also and deal with the speedo offset. Steve This message was edited by len47merc on 9-2-15 @ 3:19 PM
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| Jone | -- 09-02-2015 @ 7:06 PM |
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Tire size is 670-15 American Classic bias look radials. I guess I can live with it knowing I'm 10% low on speed. This message was edited by Jone on 9-2-15 @ 7:32 PM
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| CharlieStephens | -- 09-04-2015 @ 1:32 PM |
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Before you start switching gears on the torque tube check your odometer. If it is correct then send your speedometer out to be repaired. Charlie Stephens
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| TomO | -- 09-05-2015 @ 7:45 AM |
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Typically the Ford speedometers read high about 5%-10%. If yours is reading low, I would try lubricating it. My speedometer has a small plug on the top of the housing where the cable plugs in. Remove the plug and there is a felt wick that should be saturated with a light oil. Most of the era speedometers have this oil reservoir and wick. While you have your speedometer out, lube the cable also. Use a graphite based lubricant. Tom
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| Jone | -- 09-05-2015 @ 9:54 AM |
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Thanks TomO, I'll try that. I just had the speedo cable replaced, I don't know if he lubed it tho. Yes, I paid a mechanic to do that job, It was very difficult to do with the car up on jack stands, he has a lift. Charlie, I'll check the odometer next time I'm out with the car. I do not intend to replace the gear.
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