While taxiing a B767-300 for takeoff; Captain 'feels a bump' for the second time as he turns the tiller to the left and lines up with the runway. Plane does a lot of shaking on takeoff. Captain aborts takeoff. Aircraft is towed back to the gate.

Narrative

Nose wheel steering lost while turning on the runway for takeoff. I shut down the runway. I felt a very; very slight bump in the tiller [steering wheel] when I turned the aircraft to line up with the runway. I thought to myself; did I feel that. It was that soft. I continued the takeoff. [I] told the First Officer 'your throttles.' Just as we were transferring aircraft control; I bring the tiller to the left and feel it again; I think. It is so soft of a bump. I say; 'something is wrong; stop.' We transfer aircraft control back to me and I instruct the First Officer [to] tell Tower we have a problem. I ask another carrier who is behind me; 'how does my nose gear look'? He says it appears to be centered. I think; good; no undo stress on the nose landing gear. I then tell Tower; give me a minute; I want to think about this. I move the tiller ever so slightly to the left and felt the bump again. The other two times I was not sure did I feel something; the plane does a lot of shaking on takeoff. This time there is no doubt there is something wrong. The First Officer tells Tower; we cannot move or taxi. I have the First Officer call Maintenance. Maintenance shows up and asks me to try to move the tiller. I ask first. Pin the nose landing gear; which he does. Tug back to the gate.