A snapped lift cable takes one side of the door out of the counterbalance instantly. The door stops crooked, one corner sits low in the opening, and the cable hangs slack or coils near the drum at the top. Stop using the opener, because every cycle from here drags the door harder into the track.
How a cable gives out
Each side has a galvanized aircraft cable running from the bottom bracket, up the vertical track, to a grooved drum on the spring shaft. The drum winds it in as the spring unwinds. Two spots do the hardest work and two spots break: the loop at the bottom bracket, sitting inches from damp concrete, and the bend where the cable enters the drum and flexes on every trip.
Cables rarely part clean. They shed strands first, so you get a fuzzy patch, then a rust bloom, then a kink, then failure. The noise at the moment it lets go is a hard slap, not the firecracker bang of a spring.
The salt-air version of this failure
West of I-5, through Harborside, the Bayfront streets and down toward Otay, cables fail differently. The outer strands stay bright while the core corrodes under the galvanizing, so the cable looks serviceable from the driveway and then goes with almost no warning. Damp mornings through May and June keep the bottom of the track wet for hours, and the bottom bracket loop is exactly where that moisture sits. On doors that close to the bay, cables get replaced on age and exposure rather than on how the surface looks.
Telling it apart from a broken spring
- Cable: the door tilts, one side rides higher, loose wire is visible, and the opener may still run.
- Spring: the door stays square but feels like dead weight, and there is a two to three inch gap in the coil above the opening.
- Both together is common, because a spring letting go drops the door fast enough to throw a cable off its drum.
What you can do, and the part to leave alone
Unplug the opener so nobody sends the door anywhere. Park outside. Photograph both drums from a step back, since that picture tells a technician whether the cable is out of the groove, frayed, or gone. If the door is stuck up and crooked, leave it up.
Do not pull the release cord and try to walk a crooked door down by hand. With one cable gone the whole weight hangs off the other side, and the door can rack, jump the track, or land at an angle. Never loosen a bottom bracket either. It anchors the cable under full lift load even with the door on the floor.
Cost and the repair itself
Cables get replaced as a pair, since both wore the same hours. A pair runs an estimated $145 to $245. If the drum grooves are scored or an end bearing has gone dry, add an estimated $165 to $275 for a drum and bearing. Off-track correction, where the door has jumped, is an estimated $155 to $295. Treat these as guide figures.
Leave the door where it stopped, keep vehicles out from under it, and have the balance and travel limits reset once the new cables are wound on.