Torsion Shaft

A torsion shaft is a solid or hollow steel rod that sits above the closed garage door. It is typically 1 inch in outside diameter on residential systems. The rod runs through the center bore of every torsion spring on the assembly. It is supported at each end by the end bearing plates and at mid-span by the center bearing plate.

When the door closes, the spring coils grip the shaft through set-screw cone fittings. As the door opens and the spring releases tension, the coils unwind and spin the shaft. The shaft then turns the cable drums at each end. The drums wind up the lifting cables and pull the door upward.

What mounts on the shaft:

• One or two torsion springs, each gripped by a winding cone and a stationary cone
• A cable drum at each end, pinned with a set screw so it turns with the shaft
• The center bearing plate's bearing, letting the shaft spin freely at mid-span
• End bearing plates at each end for outer rotational support

Residential shafts are 1-inch solid or hollow steel. They span the full door width plus a few inches for the drums. Heavy-duty or commercial systems use larger shaft diameters to handle the higher torque demands.

How a shaft fails: Steel shafts rarely break outright. The common problem is bending. This happens when a drum is misaligned, or when a broken spring slams the shaft under unbalanced load. A bent shaft causes uneven cable winding. The door then travels crooked and wears the rollers and tracks faster than normal.

For example, a 16-foot wide, 7-foot tall steel door weighing about 175 pounds uses a 1-inch shaft roughly 14 feet long with two springs and two cable drums. Getting the shaft length right matters for proper drum alignment.