I have a 2002 Expedition. I am planning to go from 3.31 to 4.10 gears. The tire size will remain the same. I was told by the FORD driveline mechanic that I would not have to recalibrate anything since the tire size will remain the same and the speed sensors are actually the ABS sensors, which are located after the gear reduction. Is this true? I have the 4R100 tranny with the 9.75" differential.

Thanks,

 

I just found out that the speedometer reading actually comes from the speed sensor on the tail housing of the 4R100 and not the ABS system. This means that I WILL have to recalibrate the speedometer either by reflashing the PCM or by using a stand alone recalibrator.