Cable Drum

A cable drum is a precision-machined or cast aluminum spool mounted at each end of the torsion shaft on a garage door. Each drum has a helical groove machined into its face that matches the cable diameter and guides the lifting cable into a tight, even wind as the door opens.

The relationship between the cable drum and the torsion spring is direct: when the door closes, the spring winds up and stores energy while the drum unwinds and pays out cable. When the door opens, the spring releases that stored energy back through the shaft to the drums, which wind the cable and lift the door. The drum diameter is sized so that one revolution of the shaft lifts the door a precise amount, matching the spring's torque output to the door's weight throughout its travel.

Drum sizing matters: Cable drums are not universal. They are sized for specific door heights and lift types. A standard-lift drum is matched for a door that travels the standard radius into horizontal track, while a high-lift or vertical-lift drum has a different profile to suit the extended vertical travel. Using the wrong drum can cause the door to bind, the cable to jump the groove, or the spring to be unevenly loaded.

Common failure modes include cable jumping out of the drum groove (usually from a worn groove or incorrect spring tension), the cable fraying where it exits the drum, and the drum set-screw loosening on the shaft. A loose drum causes one side of the door to travel faster than the other, putting diagonal stress on the sections. All cable drum service requires releasing spring tension first.