1955 F100 Speedometer help needed

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Mar 4, 2021 | 01:53 AM

#16

Mr. Newbie

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Did some more testing. Took my GPS prepared a defined route noted the numbers on the odometer and went for a nice ride. Mife wife was taking notes of the speed shown at the GPS when I told her. So were checking the speeds up to 80 mls(10 mile increments), each several times and found the following (readout values are the average of 10 samples taken).

Strange that it shows too high at low speed and too low at high speed, only a small area where it is correct.
I contacted the guy who fixed the speedometer and we agreed that he will do another check on the calibration.
So far the good thing is that no matter what speed the speedo shows all I need to do is add 20 and know pretty much close the speed I drive in km.
Checking the odometer after the trip showed that it is about 3% off which is absolutely OK from my point of view. So I can be pretty much sure that my gear setup at the transmission is OK.

Uwe

Apr 23, 2021 | 04:46 AM

#17

Mr. Newbie

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Finally made it to thee guy to re-check the speedo. 1000 rpm it showed 60, 500 rpm it showed 30, odo 1005 to the mile. So I would say the thing is on the spot, but when in the truck it's still showing the same results as shown below.
Might just live with it, at least I know how fast I am.

Uwe

Apr 23, 2021 | 09:08 AM

#18

Ken Newman

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From: Queen Creek AZ

I forget if you told us, but are you sure you have the correct driven gear on the speedo cable. When you do the math formula that includes your tire revs per mile, is the answer 1000? In my opinion,
if the speedo test good, and is functioning okay, it has to be what's driving it.

Apr 23, 2021 | 09:24 AM

#19

Ken Newman

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From: Queen Creek AZ

Can you see in the hole for the speedo cable on the transmission what color the drive gear is? Mine was brown, and had 8 teeth. The new 7 tooth gear is yellow. My 20 tooth driven gear is black.

Apr 25, 2021 | 04:33 AM

#20

Mr. Newbie

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Hi Ken,
the drive gear is yellow (so should be 7), my driven is 17 and with my rear end being a 3.50 with 235/75R15 this part of the setup should be good. I guess the "correct " working odometers proofs that.
Maybe it is just a 66 year old, worn speedo, of which nobody knows how many miles it actually has seen.

Best regards
Uwe

Apr 25, 2021 | 09:02 AM

#21

Ken Newman

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From: Queen Creek AZ

Dang it,
Sounds perfect. That's frustrating to say the least. Is your cable the original one? Just grasping for anything that may help.

Apr 25, 2021 | 09:05 AM

#22

Ken Newman

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From: Queen Creek AZ

Too bad you can't borrow another speedo to see if it acts the same way.

Apr 25, 2021 | 10:49 AM

#23

Mr. Newbie

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I doubt it is the original cable, with the drivetrain being replaced I would guess somebody might change that cable too. Maybe I can borrow a speedo, heard a rumor that another guy in our town just got a mid 50s F100.