A torsion spring counterbalance system consists of one or two tightly wound up springs on a steel shaft with cable drums at both ends. The entire apparatus mounts on the header wall above the garage door and has three supports: a center bearing plate with a steel or nylon bearing and two end bearing plates at both ends. The springs themselves consist of the steel wire with a stationary cone at one end and a winding cone at the other end. The stationary cone is attached to the center bearing plate. The winding cone consists of holes every 90 degrees for winding the springs and two set screws to secure the springs to the shaft. Steel counterbalance cables run from the roller brackets at the bottom corners of the door to a notch in the cable drums. When the door is raised, the springs unwind and the stored tension lifts the door by turning the shaft, thus turning the cable drums, wrapping the cables around the grooves on the cable drums. When the door is lowered, the cables unwrap from the drums and the springs are rewound to full tension.
In 1992 the United States Consumer Product Safety Commission released new rules for automatic garage door openers. Anything manufactured after 1993 was required to include either an electric eye (a pair of sensors that detect an object obstructing the doorway) or a wall-mounted control button that users hold down in order to close the door entirely. Most manufacturers opted for the electric eye method, sometimes referred to as safety sensors.
As noted above, set-screw clamping may have distorted the cross-section of the shaft and made it difficult to slide off all the hardware. With the shaft on the floor, it may be possible to restore enough roundness to proceed, using compensating clamping force to the distorted area via a machinist's vise, an arbor press, a hydraulic shop press, etc., on the shaft body. Burrs and other slight distortions on the shaft can be filed off with a hand file or touched with an abrasive wheel on an angle grinder. At some point, the condition of the shaft may just be degraded enough that it ought to be replaced.
As in an elevator, the electric motor does not provide most of the power to move a heavy garage door. Instead, most of door's weight is offset by the counterbalance springs attached to the door. (Even manually operated garage doors have counterbalances; otherwise they would be too heavy for a person to open or close them.) In a typical design, torsion springs apply torque to a shaft, and that shaft applies a force to the garage door via steel counterbalance cables. The electric opener provides only a small amount of force to control how far the door opens and closes. In most cases, the garage door opener also holds the door closed in place of a lock.
First and foremost, a garage door, by design, contains springs designed to balance your door and make it easier to lift. Those springs are under incredible amounts of tension. If a spring breaks or is improperly released, it can cause incredible and potentially fatal injuries. Keep in mind, when working on a garage door spring, it is likely that your face and head will be close to it, meaning that your most sensitive area will be in the direct path of the released spring.