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Cable Respooling and Drum Alignment
Lift cables connect the bottom of the door to the cable drums on the torsion shaft. They carry the spring force to the door, and when one leaves its drum the door immediately becomes unsafe.
How the system works
Each drum has a helical groove. As the shaft rotates, cable winds onto or off the drum in a single controlled layer. Both drums must wind identically, because any difference in effective length lifts one side of the door before the other.
Why cables come off
- The door was allowed to close onto an obstruction, slackening the cable enough to jump the groove
- Spring failure released tension suddenly
- The door has been operating out of square, so one cable slackens at some point in travel
- The drums were not set to equal tension at installation
- Corrosion stiffened the cable so it no longer seats cleanly
Symptoms
The clearest sign is a door sitting visibly crooked in the opening, one side higher than the other. Others include a cable visibly loose while the door is closed, a grinding sound near the shaft, or a door that binds hard at one point in travel.
Restoring the cable
Spring tension is wound down under control before any work on the cables. The door is secured. Cable is seated correctly in the drum groove, the drum is set against the bearing plate at the correct position, and set screws are tightened to specification. Both sides are then tensioned equally before the springs are rewound.
Equal tension is verified by lifting the door by hand and confirming it rises level, and by checking that the bottom of the door meets the floor evenly across its width.
Cable condition
A cable that has come off is inspected rather than simply reseated. Cable that has been running under abnormal load frequently has broken strands at the drum end or crushing where it jumped. Fraying anywhere along a lift cable warrants replacement rather than reuse, and cables are replaced in pairs for the same reason springs are.
Coastal note
In salt exposed environments, cables corrode from within the strand bundle where inspection is difficult. Stiffness, discolouration and a cable that no longer lies flat are all indications that internal corrosion is advanced.