Defect
Over time, a damper inside the driveshaft may move and cause a vibration. If you continue driving with this vibration, the driveshaft could break and cause a loss of power to the wheels. Additionally, the truck could move when the transmission is in Park and the parking brake is not used. Note: This recall only affects certain 4x4 models with a 176" wheelbase, and a 4.1 or 4.3 rear axle ratio.
Safety Risk
A loss of power to the wheels could increase the risk of a crash. A parked vehicle that rolls away could also create the risk of an injury or a crash.
Remedy
Ford will notify owners by mail and instruct you to take your truck to a dealership to replace the driveshaft.