Speedometer and regearing
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Senior User
Joined: Jun 2015
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From: Littleton, CO
Speedometer and regearing
I've got a 9.75 rear end with a 4r100 transmission and 4wd.
I've been thinking about regearing.
I've searched the forum about gearing and its effect on the speedometer. It appears that the consensus is that you need a programmer to fix it but I'm not convinced.
Isn't that the speedometer gear attached to the side of the ring gear? And the ring gear is going to turn at the same rate as the tires. The pinion gear is going to be turning faster and thus the transmission and engine.
If that's the case, the speedometer shouldn't be effected, correct?
What am I missing?
I've been thinking about regearing.
I've searched the forum about gearing and its effect on the speedometer. It appears that the consensus is that you need a programmer to fix it but I'm not convinced.
Isn't that the speedometer gear attached to the side of the ring gear? And the ring gear is going to turn at the same rate as the tires. The pinion gear is going to be turning faster and thus the transmission and engine.
If that's the case, the speedometer shouldn't be effected, correct?
What am I missing?
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
I believe the speedometer and engine control computer get vehicle speed information from the output shaft speed (OSS) sensor on the transmission. The tone ring in the photo you posted is for the brake system. That's why changing gears will affect the vehicle speed signal.
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