F1 speedometer

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Jun 11, 2017 | 10:58 AM

blsd49

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From: Sandpoint, in north Idaho

F1 speedometer

So the speedometer in my 1949 F1 has never registered the correct speed. It hasn't been a big concern considering how I drive it but lately have thought I would like to correct it if I could figure out the problem. It works smoothly but to get the correct speed I have to multiply the shown speed by 1.42.
So when it shows 32 mph it really is going 45; 39mph =55 and 42mph =60.
Any ideas?
Thanks, Brian

Jun 11, 2017 | 11:19 AM

ALBUQ F-1

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From: NM

Is the drivetrain stock? That's a HUGE correction. I switched from 3.92 to 3.50 gears and only have to do about a 10% correction. There must be something inside the speedo that is causing your calibration to be so far off. Even if the trans had been swapped from a bigger truck with steeper gears (do you have a spur-gear 4-sp?) that truck would have been near 6:1 gears to make such a difference.

Jun 11, 2017 | 11:51 AM

blsd49

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From: Sandpoint, in north Idaho

All stock, I 6 with a 3 speed.

Jun 11, 2017 | 12:05 PM

schoo

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From: placer county usa?

Here is a pic of the back side

I would clean and lube the cable and a little oil at the back of the speedo

Jun 11, 2017 | 05:29 PM

blsd49

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From: Sandpoint, in north Idaho

All that is good. The cable and needle work smoothly. My thought has been that it has to do with calibration though I have never heard that they can be calibrated or that possibly the gear at the end of the cable that goes into the trans has the incorrect number of teeth?

Jun 11, 2017 | 10:41 PM

ALBUQ F-1

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From: NM

There were only a couple of gears available for the light duty trans, but it would be worth checking to see which one you have. Count the teeth.

Jun 11, 2017 | 11:19 PM

blsd49

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From: Sandpoint, in north Idaho

Ross,
I have thought of that and will do that the next time I am laying under the truck....another reason why I need to raise the ceiling in the shop and install a lift!
But then I thought , maybe incorrectly, that if what I have was the wrong number of teeth then they wouldn't mesh?

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Jun 12, 2017 | 12:17 AM

blsd49

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From: Sandpoint, in north Idaho

Ross,
I think it is a light duty trans and even though I have had this truck for 43 years I'm not positive.

is there an easy way to check?

Jun 12, 2017 | 06:20 AM

#10

haywoodya69

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Maybe you have the wrong size tires on truck?

Jun 12, 2017 | 08:17 AM

#11

blsd49

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From: Sandpoint, in north Idaho

Stock rims with 650/16 tires.

Jun 12, 2017 | 08:41 AM

#12

cowdog86

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Joined: Aug 2016

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From: Miles City, Mt

With that big of a differance it sounds more a differential gear ratio. Think about it, there aren't that many components. My F3 I changed the driven gear down one tooth to accommodate the 16" tires vesus the 17" stock and it came out just fine. I doubt it has anything to do with the speedometer itself.

Jun 12, 2017 | 09:10 AM

#13

bobj49f2

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Joined: Jan 2001

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From: SE Wisc. (the Rust Belt)

I have 750/16 on my F-2 and it knocks my speedo off by about that much. I rarely pay attention to the speedo anyways, it always seems everyone else is flying by while I'm enjoying the drive.

Jun 12, 2017 | 11:00 AM

#14

NumberDummy

Ford Parts Specialist

Joined: Nov 2006

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From: Simi Valley, CA

1948/52 F1, 3 Speed Light Duty, 3.73-1 rear axle ratio, 6.50 x 16 tires:

21C-17285-B .. 8 tooth Speedometer DRIVE Gear / Obsolete ~ 24+ available NOS

O1Y-17271-D .. 21 tooth Speedometer DRIVEN Gear / Obsolete ~ 1 available NOS
--------------------------------------------------------------------------------------------
1948/52 F1, 3 Speed Light Duty, 3.92-1 rear axle ratio, 6.00 x 16 tires:

8D-17285-B .. 8 tooth Speedometer DRIVE Gear / Obsolete ~ 1 available NOS

O1Y-17271-F .. 23 tooth Speedometer DRIVEN Gear / Obsolete ~ 2 available NOS

6.50 x 16 tires not listed in the truck parts catalog for this application.