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02-14-2021, 07:08 PM | #1 |
Junior Member
Join Date: Apr 2016
Posts: 1
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47 pickup 100vs60 mph speedometer
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
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02-14-2021, 07:41 PM | #2 |
Senior Member
Join Date: May 2010
Location: So Cal
Posts: 8,743
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Re: 47 pickup 100vs60 mph speedometer
Do the odometers read accurately?
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02-14-2021, 09:16 PM | #3 |
Member Emeritus
Join Date: Nov 2012
Location: Wichita KS
Posts: 16,132
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Re: 47 pickup 100vs60 mph speedometer
No idea on your speedometer issue, but welcome to the Barn!
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02-14-2021, 09:56 PM | #4 |
Senior Member
Join Date: Dec 2014
Location: Columbus, IN
Posts: 1,406
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Re: 47 pickup 100vs60 mph speedometer
There is a chart in the "Green Bible", Ford Service Parts catalog, that shows the correct speedometer gear for the rear axle ratio and tire size. A part of this chart is shown in this discussion topic on post #10,
https://www.fordbarn.com/forum/showthread.php?t=294334 Ps: welcome to the Ford Barn. Last edited by Zeke3; 02-14-2021 at 09:57 PM. Reason: added Ps |
02-14-2021, 10:11 PM | #5 |
Senior Member
Join Date: May 2010
Location: upstate SC
Posts: 2,963
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Re: 47 pickup 100vs60 mph speedometer
go to the rear axle housing and look at the bottom rib on the input side--there will be two number located there, may need to scrape off accumulated crud to read--this is you rear axle ratio. divide bigger number by the smaller and voila!
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02-14-2021, 10:48 PM | #6 |
Member
Join Date: Dec 2012
Location: Spokane Valley, WA
Posts: 92
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Re: 47 pickup 100vs60 mph speedometer
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Don't know why one may work and why one won't.....too technical for this cowboy!! |
02-14-2021, 11:47 PM | #7 |
Senior Member
Join Date: May 2010
Location: From Chicago. Now Nashville
Posts: 206
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Re: 47 pickup 100vs60 mph speedometer
Maybe someone put a 100 mph faceplate on a 60 mph speedometer? I think I read somewhere the speedometer can be recalibrated, so you could make it a 100 mph, if they really are both indeed 60 mph.
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