GoFastBroncos.com

I hadn't seen this addressed...and I assume this is for guys that are not running gears to correct for different tire sizes, but I figure you could probably use this to get the speedo more accurate with tire/gear combinations

http://www.ford-trucks.com/article/idx/ ... RONCO.html

1. Check whether the conversion constant in the speedometer is correct with the following procedure:

Press and hold the RESET button on the front of the speedometer while turning the key to RUN.
Release the RESET button. The pointer will prove out and some codes will appear on the odometer display. If an "E" is on the left side of the display, the module is programmed for English display mode and should have English graphics (mph). A lower case "o" signifies an overseas (metric) graphics (kph). Verify the graphics and display modes agree. (The number appearing after the type is the microprocessor revision level and is not used in this test.)
Rress and release the RESET button again. The conversion constant and the word CAL will be shown on the odometer display.
Check the conversion constant shown on the odometer display with the chart below and verify the correct constant is entered.
Turn off the key to exit this test.
2. Reprogram speed conversion constant using the following procedure:

Locate the dealer mode programming enable single-terminal connector. The connector is located at the bottom of the instrument panel below the center of the glove box. On all vehicles, the dealer mode enable wire is Circuit #567 (LB/Y).
Insert metal clip in service wire panel connector. Clip other end to vehicle ground while the key is in the OFF position.
Turn key to RUN (not crank) position while holding down the trip odometer RESET button on speedometer. Release RESET button.
Speedometer will prove out (sweep across dial and back). The English/Metric and revision levels will be displayed. The last number of the display is the dealer mode programming lockout count. This count shows the number of allowable conversion constant changes remaining. When the count is zero (0), no additional changes can be made to this instrument cluster. If a conversion constant change is required, a service instrument cluster must be ordered. Refer to this section for ordering information.
Press and release RESET button again and PSOM conversion constant (without the decimal point) followed by the word CAL.
Press and release the odometer SELECT button as many times as necessary to change conversion constant to the correct value.

NOTE: Pressing and releasing the RESET button to lock in the new Conversion Constant reduces the number of times the PSOM can be reprogrammed by one count. The module can only be reprogrammed six times. If you change your mind and want to go back to the old conversion constant, turn the ignition switch off before you lock in the new constant.
When the correct new value is displayed in odometer window, press and release the RESET button to lock in the new conversion constant.
Turn the key off and remove the ground wire. Verify proper speedometer operation.

To find conversion constants for tires with 15 inch rims that are not listed in chart, above multiply the revolutions per mile (at 45mph) of your tire times .0135. For 16 inch rims multiply by .015. The revs/mile can be found at your tire manufacturers web site. There are slight variations in revs/mile per tire manufacturers, but using one like the popular BFG A/T (see below) will get you very close.
Example: BFG AT 33x12.50R15LT/C
Revs/mile= 636
636 rev/mile X .0135 = 8.59
8.59 would be your conversion constant
Here is a listing of popular oversize BFG All-Terrain tires with conversion constants:

Tire Size Revs/mile (at 45mph) Conversion Constant
30x9.50R15LT/C 705 9.52
31x10.50R15LT/C 677 9.14
32x11.50R15LT/C 656 8.86
33x12.50R15LT/C 636 8.59
35x12.50R15LT/C 599 8.09

Nice! Thanks for posting this. I need to re calibrated mine but that all sounds super confusing to me. Lol. Who's done this before?

Found another link seemingly with more info

http://www.supermotors.net/registry/media/76023

I have. theres a calculator cruising around the internet that i used. Its accurate too. Trust me its not as difficult as it looks.

It easy, took me about five minutes. And the way the vss works it doesn't matter what gears you have, only tire size. The vss picks up the signal at the diff so one rotation with 3.55 is still one rotation with 4.88s. I went to tire rack and got my tires rpm's or rotations per mile. Used the calculator and punched in the code. This also helps when running an e4od as it corrects the electronic shift points to your tire size.

Thanks for the links and info guys. I calibrated mine last night. Not sure what I was thinking when I originally read the links but this was SUPER easy! Took it out for a test drive and the speedo and odometer were spot on confirmed by my gps. Is it this easy to calibrate rangers too?

Another item on the to do list... Thanks!

Yes very easy to do. One question though. I thought gear ratio had nothing to do with this. I thought only tire size effects the speedo not gear changes, but I've been wrong many times before.

Gear ratio doesnt matter. If you have a d60 there is an additional figure you have to do but other than that there isnt a change.

The only time gear ratio would matter is if you where to use a vss relocater that reads off of the pinion speed and not the ring speed.

If this corrects the shift points in the e4od does that mean better mpg?

And keeps the motor in the power band.

Finally got around to doing this today!! Thanks for the info guys.

Great video if you are at all unsure what plug and what to do for the PSOM/Speedo calibration!

http://www.youtube.com/watch?v=Wa0AQExCuR0

Bringing back the dead. How do you do the math when you run the vss relocated to the Tcase. I get how to do it when it's still in the axle but this is throwing me through a loop.

Arent the # of magnets in the vss mean to correct for the gears you're running by matching the cycle count?

So here is what I got for the conversion constant. The conversation constant for a 35 BFG is 8.09.

But that's for 599 revs per mile, and 102 pulses per rotation. So 102 x 599 is 61,098 pulses per mile.

So the vss kit has 28 pulses per driveshaft rotation. So at 599 revs per mile x 4.86 (my gear ratio) x 28 is 81,511 pulses per mile.

So I'm taking the conversion constant I need is 8.09. So I'm taking 8.09 x 81,511 then dividing by 61,098 which equals 10.79.

Does that sound right?

Yes but you can just do ((4.86x28)/102)*8.09

Well that is a MUCH easier way to do it. I'll still ended up with that number though!! Haha thanks Travis!

Good thing I checked again. The tone ring is 108 teeth!

So 10.15 is what I need. I'm gonna give it a shot and report back.