Speedometer vs Odometer Error?
#1
02-03-2012, 08:07 PM
Speedometer vs Odometer Error?
I have two data points with respect to speedometers, and therefore odometers, on our pickups: Dad's '81 and the '82 Explorer I recently sold. Both had errors in the speedo or odo as follows:
), it seems that you get something like a 10% error in these units. However, you can have it in the speedo, in the odo, or split over the two.
Which leads me to two questions:
- Dad's speedometer shows ~107% of actual, meaning that an indicated 65 is actually 61 MPH. But, the odometer is very accurate and shows 99.4 miles when driven an actual 100 miles for an error of .6%
- The Explorer's speedometer was very accurate, showing 98% of actual, meaning +1 MPH at 60. But, the odometer only showed 90 miles when driven 100 miles, for an error of 10%.
), it seems that you get something like a 10% error in these units. However, you can have it in the speedo, in the odo, or split over the two.Which leads me to two questions:
- Is this typical of these units? Do the others of you have similar inaccuracies?
- Is there anything that can be done? Is there any way to calibrate them?
#2
02-03-2012, 08:18 PM
My speedometer ('80 F-150) is quite accurate; it reads exactly the same as the radar-based 'YOUR SPEED IS' sign down the road from me. I suppose it's possible that the radar is reading low or (more likely) high, but it's also very close to my car as well.
As to the odometer, I've never tried to test it. But I was shocked at how simple the odometer was when I had my instrument cluster open last week; I wasn't looking for adjustments, but I'd be surprised if there was one...that's how basic it appeared.
As to the odometer, I've never tried to test it. But I was shocked at how simple the odometer was when I had my instrument cluster open last week; I wasn't looking for adjustments, but I'd be surprised if there was one...that's how basic it appeared.
#3
02-03-2012, 08:42 PM
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I have two data points with respect to speedometers, and therefore odometers, on our pickups: Dad's '81 and the '82 Explorer I recently sold. Both had errors in the speedo or odo as follows:
), it seems that you get something like a 10% error in these units. However, you can have it in the speedo, in the odo, or split over the two.
Which leads me to two questions:
- Dad's speedometer shows ~107% of actual, meaning that an indicated 65 is actually 61 MPH. But, the odometer is very accurate and shows 99.4 miles when driven an actual 100 miles for an error of .6%
- The Explorer's speedometer was very accurate, showing 98% of actual, meaning +1 MPH at 60. But, the odometer only showed 90 miles when driven 100 miles, for an error of 10%.
), it seems that you get something like a 10% error in these units. However, you can have it in the speedo, in the odo, or split over the two.Which leads me to two questions:
- Is this typical of these units? Do the others of you have similar inaccuracies?
- Is there anything that can be done? Is there any way to calibrate them?
For the Odometer, you need to replace the cable drive gear with one of the correct color. You can get it close, but you cant get it 100% unless you are real lucky. Give or take 0.5 per mile is ideal, but 1 mile variance is acceptable.
For the speedometer, there is a spring on the front of the speedometer. You have to remove the face and the needle (being careful not to break it) and turn the spring either left or right to slow it down or speed it up.
What I have done is get a variable drill and set it up and lock it to turning the speedo at 60 MPH. Then by using a clock, make sure at 60 MPH the odometer is turning 1 mile every minute. If not adjust the spring by turning it slightly either left and right and try again. It's very tedious, you will have to speed or slow the drill up or down to match the reading of 60 MPH for every adjustment, and I don't recommend it without having patience.
After you get the speedometer calibrated with the odometer on your bench, IE turning 1 mile a minute at 60MPH...
Then you can adjust the odometer by swapping cable gears.
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GOVTMOD
1973 - 1979 F-100 & Larger F-Series Trucks
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