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hi, all. I finally got my 47 1/2 ton on the road after collecting parts for 19 years!! I have 2 instrument clusters, one with a 60 mph speedo,the other a 100. I want to use the 100 mpg cluster,it's nicer and is made more for a 1/2 ton. problem is that it shows about 60% of my speed,so I know my truck it set up for the 60mph speedo. I have a 20 and a 18 tooth driven gear for the transmission, but neither one changes the speedometer read out by much, maybe 8 mph. the transmission is a 1947 3-speed ,on a 52 flathead V8. don't know about the rear end,but it looks original with the 47 frame. So how do I get my 100mph speedometer to read right? or do I just suck it up and put in the 60mph speedo. I will send pictures of truck I know you guys all want, thanks , Tony
Before condemning a speedometer, lubricate and calibrate it. I did a long winded write up in another thread on a method to calibrate old cable drive speedos.
link: https://www.ford-trucks.com/forums/1...l#post19388155
thanks for info! I just reread my thread, I got the speedometers mixed up, with the 100 mph installed at 60mph it reads 100 mph, so I know truck is setup for a 60 mph speedometer. I don't know why tho,it's got original rear end and 3 speed tranny for a 1/2 ton ,I will have to crawl under and see if I can find some numbers on the rear end I guess, It is a banjo rear tho. thanks again , tony
Interesting. My dad had the opposite problem, he had an original 47 half ton pickup with factory four speed and 60 mph speedometer. It showed 43 when the truck was going 60.
Have you checked the Green Book for the proper driven gear for your tire size and rear axle ratio?
First, get the odometer to read one mile per mile (roads with mile markers are great for this), then adjust the speedometer itself. You may need a correction adapter like 5150BAT showed a few posts back.
I may need a different drive gear because the speedometer would be reading correctly if it was a 60 mph speedo. I have tried 18, and 20 tooth driven gears without mush change, maybe 10 mph difference. the drive gear is a 6 tooth. I may try an 8 tooth sometime in the spring,I live just south of Buffalo ny in the snow belt so I have 3 feet of snow to watch melt first. I still have wiring issues to keep me BZ until then here isa few of my 47. It me 19 years on and off to collect all the parts for it. the moter is a 52 , the bed is a 53,but the rest is all 46,47.I just got on the road last july. It's fun driving somthing old then me,well a few years older anyways. You guys all heled me with your ports and pictures! Thanks!! tony
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1947, 100mph vs 60mph speedometer
speedometer drive gear, and pictures! maybe
