Quote:
Originally Posted by markeb01
I'm not sure changing tire diameters is the best approach to speedo accuracy this many years after production. Too many thing may have been changed over the life of the truck. The ratio adapter noted above may help, but it might not be the ratio change you need.
A speedometer shop would be the best bet as they can simply change the plastic driven gear in your transmission to one that gets you very close to a correct reading:
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I went thru this with me truck recently. My speedometer was 5 mph slow. I changed the plastic gear by 2 teeth. If I am remembering right, I had the blue gear which is 19 teeth and had to change to the brown gear with 17 teeth. Lower number of teeth speeds up the speedometer gauge. This is the gear that is on the end of the speedometer cable where it goes into the transmission. Gears are available on line if you do not have a local speedometer or transmission shop.
Hugh