Speedometer Issues
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Trailering
Joined: Mar 2023
Posts: 22
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Speedometer Issues
I have a 1990 F-150 XLT Lariat 4WD. I had to replace my tires, so I went from the factory size of P235 75 R15 to BF Goodrich AT 33X10.5 R15. (I like the original rims, so decided to just stick with the 15").
Predictably, my speedometer is way off. When it reads about 66 or 67 I'm doing 75, and when it reads 75 I'm at almost 90. That's gonna get me in trouble!
I need to change the gear on the speedometer cable where it goes into the transmission, but I don't know how to figure out what gear (how many teeth) I need to get. Seems hard to get one, because neither of the parts houses in town can get them anymore.
Thanks in advance for any advice.
Predictably, my speedometer is way off. When it reads about 66 or 67 I'm doing 75, and when it reads 75 I'm at almost 90. That's gonna get me in trouble!
I need to change the gear on the speedometer cable where it goes into the transmission, but I don't know how to figure out what gear (how many teeth) I need to get. Seems hard to get one, because neither of the parts houses in town can get them anymore.
Thanks in advance for any advice.
Hotshot
Joined: Jul 2020
Posts: 10,468
Likes: 2,631
From: Near Salt Lake City
Each tooth is 5 miles per hour at 60 is what they taught bus in school, and it's in the books too
You might have to replace both the drive and driven gears, if you are too far off, and cannot get it correct by just replacing the driven gear on the end of the speedo cable
Ford parts used to ask us what color and what axle ratio we had when referencing gears
sounds like you need to speed up your speedo, that means I would take 2 teeth of the driven gear in your case
If you cannot get a less teeth driven gear, you need a drive gear with one more tooth (that will speed up your original gear on the cable)
You might have to replace both the drive and driven gears, if you are too far off, and cannot get it correct by just replacing the driven gear on the end of the speedo cable
Ford parts used to ask us what color and what axle ratio we had when referencing gears
sounds like you need to speed up your speedo, that means I would take 2 teeth of the driven gear in your case
If you cannot get a less teeth driven gear, you need a drive gear with one more tooth (that will speed up your original gear on the cable)
Thread Starter
|
Trailering
Joined: Mar 2023
Posts: 22
Likes: 3
Each tooth is 5 miles per hour at 60 is what they taught bus in school, and it's in the books too
You might have to replace both the drive and driven gears, if you are too far off, and cannot get it correct by just replacing the driven gear on the end of the speedo cable
Ford parts used to ask us what color and what axle ratio we had when referencing gears
sounds like you need to speed up your speedo, that means I would take 2 teeth of the driven gear in your case
If you cannot get a less teeth driven gear, you need a drive gear with one more tooth (that will speed up your original gear on the cable)
You might have to replace both the drive and driven gears, if you are too far off, and cannot get it correct by just replacing the driven gear on the end of the speedo cable
Ford parts used to ask us what color and what axle ratio we had when referencing gears
sounds like you need to speed up your speedo, that means I would take 2 teeth of the driven gear in your case
If you cannot get a less teeth driven gear, you need a drive gear with one more tooth (that will speed up your original gear on the cable)
Thanks for sharing this!
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