Lift cables carry the door's weight from the bottom brackets to the drums on the spring shaft. When one fails, the other now holds everything.
The usual causes
- Moisture and rust, most often starting at the bottom bracket
- Shock loading when a spring breaks suddenly
- Worn drums or an out-of-level shaft winding the cable unevenly
- The door hitting an obstruction, creating slack that jumps off the drum
Why it is urgent
An unbalanced door twists in its opening, stresses panels and tracks, and can drop without warning. Cables are replaced as a pair and the door is re-tensioned and rebalanced afterwards — clipping a loose end back on is not a repair.