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?

 

What color gear do you have now.

 

You can go a gear that is one tooth less than your current gear. Really, 3 mph is not bad as most cars are within 5 mph of what the speedo reads...

 

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.

 

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??????

 

Here is the colors and what they mean:


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thanks subford! and congrats on the 10K posts!!!!!

 

The calculator seems to work pretty well on this page: Ford Bronco Speedo Gearing

 

I have yellow one now. Thanks everyone!

 

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

 

ok so we got all the info on the speedo gear... What about the driven gear that goes inside the tranny or t-case tail? Is there a way to find those aftermarket or online????

 

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.

 

I ordered one and I'll let you know how is goes.

 

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.

 

The color of the gear and the number of teeth would depend on you rear end ratio and tire size (Rev per Mile).