Speedo Gear / Tooth

[haktmal]

Hi,
If I swap my 3.23 rear gear to 3.73, what speedo gear tooth should I get to adjust for the mileage error?

Thanks.

 

[410Fortune]

YOU NEED TO KNOW WHAT COLOR YOUR CURRENT GEAR IS.

Check out the info here aout speedometer correction:

www.therangerstation.com

Also try a search feature. The correct gear for you depends on more then just 3.27 to 3.73. tranny type, and tire size also have some to do with it. I can tell you I have a 21 tooth gear with 4.10 ring and pinions with 31" tires and my speedo is DEAD on.

 

[Robert]

Originally posted by haktmal
Hi,
If I swap my 3.23 rear gear to 3.73, what speedo gear tooth should I get to adjust for the mileage error?

Thanks.

You can't get a new speedometer gear. Starting with the '98 Explorer, Ford did away with the transmission/transfer case mounted VSS and started using the RABS to monitor the vehicle speed. You need to have Ford reprogram your speedometer with their NGS Star Tester. I have heard that someone now makes a speed calibrator that will also let you change your speedometer indication. Do a search here and you should find the information.

 

[Okrazie1]

Actually, changing the gears in a '98 or newer doesn't affect the speedometer. As Robert said, the RABS (Rear Antilock Brake Sensor) is used to get the signal for the speedometer. The toothed ring which creates the pulse is mounted to the differential, and changing the gears will not affect the rotational speed of the ring. I just recently changed from a 3.27 to a 4.10, and the speedometer was not affected.

 

[MeatyCrab]

But what about changing tyre sizes? Surely that will require somesort of adjustment, right?

Anyone have the lowdown on that?

 

[Okrazie1]

Changing tires would require reprogramming of the computer. However, I'm running 31's and have not had my speedo recalibrated. The odometer reads about 9.4 miles every 10 miles travelled, but whenever I drive by one of those radar speed monitor trailers (the radar setup with the big speed readout) the speed it reads is right on with the speedometer in the truck.