Pen plotter McGraw not plotting correctly

[JackiePease]

McGraw is getting stuck around half way along the y axis, and the stepper is vibrating (the one on top of the "bridge" section).
It could be that it needs a new cable as this has caused similarish? issues in the past.
Also, the bridge beam has been damaged by the bearings pushing against the side of the groove, on both the top and bottom faces, resulting in notches. I've removed the extra wheel that was added to keep the bearings running straight but that hasn't made any difference.