One problem related to driveshaft has been reported for the 1998 Lincoln Town Car. The most recently reported issues are listed below.
Excessive vibration begins at 47 mph. Frequency and severity vary with speed. At some speeds it is barely noticable. At other speeds the sound can lull you to sleep. Particurally at interstate speeds. Vibration will stress u-joints and cause fatigue and failure. Failure at highway speeds could cause loss of control resulting in accident.