A closed circuit synchronizing cylinder assembly for synchronously moving at least two external devices such that the devices move at the same rate and maintain essentially the same level within a small deviation. The synchronizing cylinder assembly has a cylinder with a movable piston and rod for each external device. The piston divides the interior of the cylinder into a rod outer diameter chamber, a rod inner diameter chamber and a third chamber. The rod outer diameter chamber and rod inner diameter chamber have equal areas and hydraulic fluid therein and third member is open to atmosphere. The hydraulic fluid in the rod outer diameter chamber of one cylinder communicates with the rod inner diameter chamber of another cylinder driving the reciprocal movement of the piston and rod. An equalizing vent located in each cylinder communicates between the rod outer diameter chamber and the rod inner diameter chamber to allow passage of hydraulic fluid between chambers to allow the cylinders to fully stroke and re-synchronize each cycle automatically.