The aircraft experienced nosewheel shimmy following a normal landing at Manchester Airport. As the aircraft entered a rapid exit taxiway at a groundspeed of 30 kt, the nose landing gear upper and lower torque links became disconnected and the aircraft did not respond to further steering inputs. The co-pilot brought the aircraft to a halt on the taxiway. The available evidence shows that the probable cause of the torque link disconnection was damage sustained to the torque link apex pin nut locking components due to contact with a towbarless tractor. A Service Bulletin is available to replace the torque link apex pin assembly with a new design, one feature of which reduces the risk of contact damage with towbarless tractors.