Speedometer Adjustment
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New User
Joined: Apr 2020
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From: Courtenay BC
Speedometer Adjustment
I've lifted my 1986 Bronco and put some 35" tires on it, the speedometer is now very off and was wondering how to fix that? I know that there is a gear in the transfer case that reads the speed but can that just be switched out or does it take more work than that?
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Nope. You are on the right track. There are numerous gears available. The Forum Sponsor carries them as I recall.
Moderator
Joined: Dec 2007
Posts: 7,986
Likes: 104
From: Boise, Idaho
It's easy to recalculate and change your speedometer gear. Especially if you have GPS on your phone (lots of free apps for that).
Go for a drive. The faster the better, so try to find a stretch of interstate/freeway.
Record what the speedometer says and what the GPS says.
Then, pull your speedometer gear out of the transfer case. It's held in by a single little bolt and goes into the tailhousing. Give it a tug once the bolt is out.
Count the number of teeth on your current gear, and then do the math:
New gear = current gear teeth * (Speedometer / GPS Speed)
So if you currently have an 18 tooth, and your speedometer says 65 when you're actually going 75.
New Gear = 18 * (65 / 75)
New Gear = 15.6
A 16 tooth gear will get your speedometer pretty close.
Go for a drive. The faster the better, so try to find a stretch of interstate/freeway.
Record what the speedometer says and what the GPS says.
Then, pull your speedometer gear out of the transfer case. It's held in by a single little bolt and goes into the tailhousing. Give it a tug once the bolt is out.
Count the number of teeth on your current gear, and then do the math:
New gear = current gear teeth * (Speedometer / GPS Speed)
So if you currently have an 18 tooth, and your speedometer says 65 when you're actually going 75.
New Gear = 18 * (65 / 75)
New Gear = 15.6
A 16 tooth gear will get your speedometer pretty close.
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