A319 flight crew experienced degraded steering after landing due to the failure of the scissor link pin.

Narrative

Just after the Captain lowered the nose on landing rollout; the aircraft started shuddering. It was at 100 KTS and the motion decreased as the aircraft slowed down. It was moderate to light shaking of the aircraft. We rolled clear of the runway on J1 and set the parking brakes. The Captain and I thought we might have had a flat nose tire. We requested Ground Crew come inspect the aircraft. Ground Personnel's initial inspection revealed nothing wrong; so we attempted to continue to taxi. We immediately knew that there was something wrong with the steering and stopped the aircraft again. We requested a tow-in and shut down the engines. We performed the tow-in checklist and then a ground tug was hooked up and we were uneventfully towed in to the gate. Further inspection showed that a pin on the scissor link aft of the nose gear had broken. Touchdown for the landing had been normal and the aircraft was tracking straight as the nosewheels were set down. The aircraft never felt out of control.