A hydraulic system for synchronizing telescoping sections of a crane boom comprising a fixed section and second, third and fourth sections that can be extended and retracted, hydraulic cylinders between the sections for extending and retracting the adjacent sections relative to one another and a control valve for each cylinder. Cables are provided between the sections such that a non-uniformity in movement of the sections causes a change in displacement of the cables which is sensed by position sensing devices to provide a hydraulic pilot signal for modifying flow of hydraulic fluid to the cylinders.