Caliberating the speedometer
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bandit76
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Caliberating the speedometer
I have a 69 F100 with a 360 engine and a C6 tranny. Recently, I had to replace a 3.25 gear ratio rear end chuck with a 3.75. I checked against a GPS speed and I'm running a bit slower that what the truck speedometer is displaying. How can I fix this? Thanks for any help.
1969 F-100
1971 VW Superbeetle
1971 VW Superbeetle
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BobbyFord
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Re: Caliberating the speedometer
You need a larger diameter speedo driven gear (more teeth).
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Mancar1
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Re: Caliberating the speedometer
Bobby knows of what he speaks. 
May your sails stay full, and your knots not slip. Unless a slip knot.
Once I thought I was wrong, but I was wrong.
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Once I thought I was wrong, but I was wrong.
Life is a banquet, and every days a feast.
68 F-250 CS 390 C-6 P/S A/C front disc. 2nd owner.
2016 GMC Terrain Denali 301 HP V-6 AWD.
2009 Silverado Crew Cab, V-8, 4X4.
DD-727
DD-806
AE-35
LSD-39
AS-41
AR-8
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bandit76
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Re: Caliberating the speedometer
Which speedo gear would I need or where could I find the info? I notice LMC has several different ones.
1969 F-100
1971 VW Superbeetle
1971 VW Superbeetle
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flyboy2610
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Re: Caliberating the speedometer
Well, the way it is, you shouldn't get a speeding ticket!bandit76 wrote:I have a 69 F100 with a 360 engine and a C6 tranny. Recently, I had to replace a 3.25 gear ratio rear end chuck with a 3.75. I checked against a GPS speed and I'm running a bit slower that what the truck speedometer is displaying. How can I fix this? Thanks for any help.
"If the women don't find you handsome, they should at least find you handy."
Red Green
If you're going to live like there's no hell...............
you'd better be right.
http://theworldasiseeit-flyboy2610.blog ... ee-it.html
Red Green
If you're going to live like there's no hell...............
you'd better be right.
http://theworldasiseeit-flyboy2610.blog ... ee-it.html
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BobbyFord
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Re: Caliberating the speedometer
I don't have a Ford parts book, but since Ford did not offer a 3.75 option for our trucks you will have to go with your application but with a 3.73 rear gear ratio. If someone here has a parts book they can tell you the correct number of teeth, if not your local Ford dealer can help you.bandit76 wrote:Which speedo gear would I need or where could I find the info? I notice LMC has several different ones.
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70_F100
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Re: Caliberating the speedometer
In order to determine the correct gear, we'll need to know what size tires, also.
Wise men talk because they have something to say; fools talk because they have to say something.--Plato
Why is it that there's seldom time to fix it right the first time, but there's always time to fix it right the second time???
That's not an oil leak
That's SWEAT from all that HORSEPOWER!!
Why is it that there's seldom time to fix it right the first time, but there's always time to fix it right the second time???
That's not an oil leak
That's SWEAT from all that HORSEPOWER!! -
fordman
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Re: Caliberating the speedometer
arent you suppose to add one tooth per so many miles per hour it is off?
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bandit76
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Re: Caliberating the speedometer
I found out the rear end chunk came out of a mid-70's ford pickup.
You got that right flyboy speedometer said I was going 60 MPH but reality I was only going 50 MPH.
@ 70_F100 I'm running 235 75 R15 if that helps.
You got that right flyboy speedometer said I was going 60 MPH but reality I was only going 50 MPH.
@ 70_F100 I'm running 235 75 R15 if that helps.
1969 F-100
1971 VW Superbeetle
1971 VW Superbeetle
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justiz00
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Re: Caliberating the speedometer
When I went from a 3.25 to a 3.0 I went 1 tooth lower on the cable side gear. The speedo is off the same as it was with the old gears (incorrect tire size). I found the info here.
http://www.ford-trucks.com/forums/90208 ... tions.html
http://www.ford-trucks.com/forums/90208 ... tions.html