Speedo Gear Swap
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Freshman User
Joined: Feb 2006
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Speedo Gear Swap
I swapped gears in the rear from 2.73's to 3.55's, now the speedometer reads high ...(44mph reading = 35 mph actual).
The speedometer gear in the tranny (5 spd manual) has 17 teeth.
How many teeth should I go to to get close?
The speedometer gear in the tranny (5 spd manual) has 17 teeth.
How many teeth should I go to to get close?
Cargo Master
Joined: May 2003
Posts: 2,561
Likes: 1
From: Earth
I went through this last summer. If memory serves, I believe the general rule of thumb was one tooth for every 5 mph change. However, the speedo will still be off a little but it will be closer. Good luck.
Posting Guru
Joined: Jan 2002
Posts: 1,346
Likes: 8
From: Baltimore
First go to http://www.tirerack.com
Pick the size of the tire you have. Then look at the chart for
how many revolutions per mile.
Then go to http://www.fordracingparts.com/download/charts/142.pdf
Insert the numbers in the formula to calculate the number of teeth for the driven gear.
Note manual trans. and older 4x4's which have the speedometer driven gear in the transfer case use the same driven gear.
Auto trans. driven gears are different.
Pick the size of the tire you have. Then look at the chart for
how many revolutions per mile.
Then go to http://www.fordracingparts.com/download/charts/142.pdf
Insert the numbers in the formula to calculate the number of teeth for the driven gear.
Note manual trans. and older 4x4's which have the speedometer driven gear in the transfer case use the same driven gear.
Auto trans. driven gears are different.
Last edited by F150xlt; May 14, 2006 at 10:35 PM.
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