A surgical instrument includes a handle, an elongated shaft and an end effector extending distally from the shaft. A tensile member is preloaded with a tensile force and extends at least partially through the shaft. A preload mechanism for adjusting the tensile force includes first and second guides in contact with the tensile member to restrain the tensile member at respective first and second lateral distances from a longitudinal axis. A third guide is disposed longitudinally between the first and second guides and is in contact with the tensile member to restrain the tensile member at a third lateral distance from the longitudinal axis. The third guide is movable to vary the third lateral distance and a corresponding length of the tensile member disposed longitudinally between the first and second guides to thereby vary the tensile force.