I own a 1998 4-wheel drive Ford Expedition. The 4-wheel drive selection switch includes options for 2-wheel drive, all-wheel drive, 4-wheel high and 4-wheel low. I understand that the “all-wheel drive” selection is a good choice for paved roads, that might have patches of ice or snow present. When the vehicle is in all-wheel drive the front tires “drag” when I am turning a corner on pavement. I understand that “dragging” while turning can be expected in the 4-wheel drive position but would not be anticipated in the all-wheel drive position. I cannot detect a difference in the all-wheel drive function versus the 4-wheel drive function. Should I expect the vehicle to maneuver smoothly around corners in all-wheel drive without the front tires dragging? Regards, Gary

 

All Wheel Drive means that you always have power to all four wheels, regardless of the conditions. Your Expedition does not have All Wheel Drive, but instead Automatic Four Wheel Drive. By choosing A4WD position, the computer measures the front and rear wheel speeds and then engages 4WD automatically when needed. You will often hear a slight clunk when it engages, but it's shouldn't be very loud or obnoxious. When it's need is done, it automatically disengages. All '99 and newer Expeditions don't have the 2WD position, so they are in A4WD unless you choose 4HI or 4LO.

 

Thank you for your quick response. I understand your explanation concerning my incorrect 4X4 terminology. I’ll change my wording to “A4WD” versus “all wheel drive”. The question still remains concerning dragging when turning a corner. Should the front tires drag while turning when the vehicle is in “A4WD”? Regards, Gary

 

The front wheels should not be producing any drag while turning unless the 4WD is activated by the computer. When you are on dry pavement, the front wheels should act as if you had the selector switch in 2WD. You may have a problem with the A4WD circuit that keeps the 4WD engaged. When I have my Expy in A4WD, there is no noticeable difference unless the computer kick in 4WD. You may want to take it to a shop and have the codes pulled from the computer. They can tend to lead you in the right direction.

 

I have an Expy 99 and an older Aerostar with A4WD, a more primative version, prone to similar problems as you describe. A commonly overlooked reason for early lockup is nothing more than unequal air pressures in the front tires. The configurational rolling difference in diameter and thus relative speed, is enough to trip the sensors into engaging the front differential and produce the drag you feel. This is especially pronounced on turns where the turning radius itself causes the wheel speeds to differ. Bottom line, check your tire pressures first before taking it in to the dealer.