One problem related to clutch has been reported for the 1999 Ford Expedition. The most recently reported issues are listed below.
A loud "knuckling" sound is often heard when turning at slow speeds. Noise comes from the front end and sounds similar to what one hears when the four wheel drive is engaged and during a sharp turn. The vehicle feels like one is driving over softball sized rocks. There also is an increase in engine rpms associated with this. Campus Ford of okemos, mi diagnosed this as a failure of the clutch assenbly in the four wheel drive. This was replaced but the problem still exists. I'm fearful that something could happen to the wheel assembly while traveling down the highway.