The rear axle horizontal mounting bolt may fracture, causing the driveshaft to disconnect. That can result in a loss of drive power or a vehicle rollaway if the parking brake is not applied.
Ford Recalls Super Duty Trucks for Possible Rear Axle Shaft Problem
A broken rear axle shaft can result in a loss of drive power or vehicle rollaway when the vehicle is placed in park. Either of these scenarios can increase the risk of a crash.