Speedo synchronized with new differentials
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Joined: Jul 2010
Posts: 12,052
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From: Media PA
You don't need to do anything, unless you also changed the tire size. The tone ring for the speed sensor pickup is mounted to the ring gear so it is turning at the same RPM as the axle/tire. So a gear change won't alter the speedo reading but a tire size change will, I've done both to my rig and my speedo remained at the factory inaccurate reading with my change from 3.73 to 4.88. But when I upgraded tires from 32" to 35" that knocked my displayed speed down below the actual speed.
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Junior User
Joined: Feb 2010
Posts: 75
Likes: 0
Well when I drive by the same sign in my car the speedo in the car and the sign agree with each other.
But if you all say that changing the differentials does not alter the speedometer or odometer than I guess all my questions are moot.
But if you all say that changing the differentials does not alter the speedometer or odometer than I guess all my questions are moot.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,725
Likes: 2,651
From: SE Florida
You can correct the speedo reading, but changing the diff ratio didn't cause it to be wrong. It takes a high end scan tool that can communicate with the computer. There is a parameter to adjust the speedo reading.
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