SPEEDO GEARS!!!
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Senior User
Joined: Aug 2009
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From: Brazoria, Texas
SPEEDO GEARS!!!
I have a 89 f150 4x4 with a i-6 and 31in tires. The original speedo gear reads that I'm going 3mph faster than what i really am. Which gear would y'all recommend getting?
FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
Depends what axle gearing you have now, if 3.55's you should have a 20t driven gear but if you have 3.08's it will be 18t for example. I changed to 1 tooth smaller driven gear on my truck when I put 31's on and the speedo is dead on with the GPS now, this makes the odometer more accurate of course and that's what you need to get accurate fuel milage calculations.
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Joined: Mar 2008
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From: Des Moines, Iowa
I just pulled my speed sensor last night because my speedometer started to "bounce." I have 3.55's in my F-250 and a pink 19t speed sensor gear. Is that standard for F-250's? or did the PO down size from a 20t for the bigger tires he had on?
Also where the heck do you get the drive gear that goes in the tailshaft of the t-case??????
Also where the heck do you get the drive gear that goes in the tailshaft of the t-case??????
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From: Des Moines, Iowa
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Fleet Owner
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From: Easton,Ks
Yellow is an 18 tooth gear.
I think you need a White gear with 17 teeth.
Ford Motorsports Also Uses This Formula:
Driven Gear Teeth = (Drive Gear Teeth x Axle Ratio x Tire Rev. Per Mile) / 1000
FourWheeler Magazine uses:
Actual MPH = (New Tire Diameter x Indicated MPH) / Old Tire Diameter
I think you need a White gear with 17 teeth.
Ford Motorsports Also Uses This Formula:
Driven Gear Teeth = (Drive Gear Teeth x Axle Ratio x Tire Rev. Per Mile) / 1000
FourWheeler Magazine uses:
Actual MPH = (New Tire Diameter x Indicated MPH) / Old Tire Diameter
Lead Driver
Joined: Nov 2002
Posts: 9,555
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From: Concord, NC
I found some using a google search a while back. I think they were around $30 or so. If you can get the Ford part number, the dealer may be able to get one for you. They had the driven gear in stock when I needed to change to the larger tooth count.
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Senior User
Joined: Aug 2009
Posts: 252
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From: Brazoria, Texas
Yellow is an 18 tooth gear.
I think you need a White gear with 17 teeth.
Ford Motorsports Also Uses This Formula:
Driven Gear Teeth = (Drive Gear Teeth x Axle Ratio x Tire Rev. Per Mile) / 1000
FourWheeler Magazine uses:
Actual MPH = (New Tire Diameter x Indicated MPH) / Old Tire Diameter
I think you need a White gear with 17 teeth.
Ford Motorsports Also Uses This Formula:
Driven Gear Teeth = (Drive Gear Teeth x Axle Ratio x Tire Rev. Per Mile) / 1000
FourWheeler Magazine uses:
Actual MPH = (New Tire Diameter x Indicated MPH) / Old Tire Diameter
I ordered one and I'll let you know how is goes.
New User
Joined: Apr 2010
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From: Western Colorado
I just bought an '87 F250 and I think the speedo is off by 10-15%. I don't know what color the gear is in the T-case, but the cable gear is maroon. Is that correct for an 87 F250 351, AT, 4WD? Thanks, Kelly.
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
The color of the gear and the number of teeth would depend on you rear end ratio and tire size (Rev per Mile).