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#1 |
Registered User
Join Date: Sep 2005
Location: Lexington KY
Posts: 64
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Calibrating speedometer???
I'm using 275/60/15 tires and my speedo shows about 9 miles an hour less than actual speed (as referenced by other vehicles). Is there a way to calibrate the unit to show actual speed?
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1971 Chevy swb Chevy trucks and import cars ![]() Last edited by Derrickbwg; 10-18-2005 at 03:09 PM. |
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#2 |
GEARHEAD
Join Date: Aug 2003
Location: MN
Posts: 6,122
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Re: Calibrating speedometer???
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If no one knows what you're doing, they can't tell you you're doing it wrong HG's Dream Car Build - Shelby Cobra Kit Build your own adjustable track bar 71 ![]() 72 ![]() HG's Plow Truck '78 ![]() Bigass Farm Truck HG's thread of miscellaneous stuff |
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#3 |
Senior Member
![]() Join Date: Mar 2003
Location: Colfax-California
Posts: 8,550
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Re: Calibrating speedometer???
9 miles an hour at what speed? Speedo calibration works on a percentage. May be as simple as a gear swap in the back of the trans
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#4 |
Registered User
Join Date: Sep 2005
Location: Lexington KY
Posts: 64
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Re: Calibrating speedometer???
at 55 and 65. I paced a car going 55 then told them to go to 65, I didn't see much difference (still about 9mph) between the two error wise. Maybe I wouldn't notice that small a diff between 10mph.
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#5 |
Senior Member
![]() ![]() Join Date: Jan 2005
Location: CA
Posts: 5,525
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Re: Calibrating speedometer???
Do you know what gear ratio you have in your rear end? It might be listed on your glovebox door options sticker. What kind of transmission do you have?
You will need to replace the speedometer drive gears located on the output shaft of your transmission, as already suggested by "hgs notes". |
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#6 |
Registered User
Join Date: Sep 2005
Location: Lexington KY
Posts: 64
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Re: Calibrating speedometer???
I'm not sure of the gearing, the tranny is a 350.
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#7 |
Registered User
Join Date: Oct 2004
Location: Walker Co. Alabama
Posts: 474
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Re: Calibrating speedometer???
One way I've found to find the percentage spedo is off is get on a road you can drive 10 miles between mile marker posts (that way you KNOW you went 10 miles). note your odometer starting and the mile marker starting. go until you have gone exactly 10 marker miles. note the distance traveled on your odometer. multiply 10 X odometer distance = percentage of accuracy example: 10 marker miles X 7.5 odometer miles = 75% accurate. You can use this to "gauge" your speed by your speedometer. if you don't want to exceed say 65 MPH and your speedo is 75% accurate then multiply 65 X 75% = 48.75 MPH on your speedometer. Before anyone says "why do all that just calibrate it
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