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Old 08-09-2017, 03:45 PM   #1
dmf6978
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Default Broken Speedo

Finally got my truck plated and registered. I am so happy, and it came back from the mechanic who said WOW this is a cool bad ass truck that runs perfect. Just had some oil filters and fuel filters changed, and the carb dialed in. Drive it home and noticed the speed didn't seem accurate.

Any ideas of which parts I would swap out to make it work again? I have not dove into my service manual of 1500 pages
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Old 08-09-2017, 04:27 PM   #2
int77345
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Default Re: Broken Speedo

like it seems to be showing to slow to fast?
the needle bounces?

this is a new problem ? or has been a problem for years ?
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Old 08-09-2017, 04:32 PM   #3
dmf6978
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Default Re: Broken Speedo

No bouncing. But it said I was going 25-30 but I felt maybe going 35-40. Just bought the truck and had it tune up. First time actually driving it today. I will keep an eye next time I drive using my gps and get a better feel of actual speeds. Good news is I found parts to,replace just in case.
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Old 08-09-2017, 09:27 PM   #4
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Default Re: Broken Speedo

Checking it against the mile markers on the side of the highway will help calibrate it.
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Old 08-09-2017, 09:37 PM   #5
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Default Re: Broken Speedo

That's good news on the overall health of the truck. A misreading speedo is small potatoes by comparison. You can stick your Tom Tom Naggigation deevyse in the winder and compare notes. Larger than stock tires can throw things off. A speedo cable that hasn't been well lubed in the last three decades can throw things off. Or your speedo gauge itself may just be ready to go ta-tas up.
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Old 08-10-2017, 05:29 AM   #6
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Default Re: Broken Speedo

I use a GPS app on my Iphone to check speedometer accuracy. If the speedometer is indeed off and needs to be corrected, we offer these inline speedometer gear boxes that will correct it.

Speedometer Calibration Gear Box - Corrects your Speedometer!

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Old 08-10-2017, 04:03 PM   #7
dmf6978
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Default Re: Broken Speedo

Very cool. What exactly does that part do? Does it come with instruction? I suppose I can remove my cable now and check it out, make sure nothing is frayed. can i lube it somehow?
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Old 08-11-2017, 06:40 AM   #8
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Default Re: Broken Speedo

It is a small gearbox that goes inline with the speedometer cable.
You put different plastic gears in it to correct the speedometer to match the tire size & final drive gearing you have installed on the truck.

Usually one can go to a speedometer repair shop in town where they put your vehicle on a roller and run the drivetrain up to speed and see how far off your speedo indication is.

Then they either change the gears in your box or if your truck does not have one, they build a box with the correct gears in it and install it on your cable and then the speedo reads correctly.

Although these trucks were built during the heyday of NASA, there is no rocket science built into them.
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Old 09-28-2017, 12:25 PM   #9
RPMCK
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Default Re: Broken Speedo

I've replaced my speedo and cable. Still I get the needle somewhere between 60-90mph while I'm rolling along at about 35mph. Any clues? I've also got the gearbox in line.
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Old 09-28-2017, 07:39 PM   #10
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Default Re: Broken Speedo

I would try and check if the mileage reads correctly, either with a GPS, or if you know of someplace with mile markers. The odometers are usually straight gear drives off the speedo cable, but the speedometers are weird magnetically coupled drives. On my Scout the speedometer does not work at all, but the odometer is dead on. Since I'm planning on re-gearing and going to bigger tires, see no point in getting the speedo fixed until then, have to take it in to a shop and not cheap. You can also find some little GPS speedometers for around 30 bucks on Amazon that plug into a cigar lighter or USB port.
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