Expedition's have a parking brake system similiar to that of a 1965 - '82 Corvette, i.e., a specially-shaped disc brake rotor that surrounds a small brake drum (which is the parking brake). According to my 1999 Ford Expedition Workshop Manual, the parking brake is NOT self-adjusting. In order to correct misadjusted brake shoes, the adjuster screw, located at the bottom of the shoes, has to be manually adjusted.

The Chilton's manual probably also contains info on the F-150 pickup, which was offered with rear drum service brakes that are self-adjusting.