Lift cable

One cable runs up each side of the door, attached at the bottom bracket and wound onto a drum on the torsion shaft. The springs turn the shaft, the drums wind the cables, and the cables lift the door.

Cables fray from the inside out where they wind onto the drum, so a cable can be close to failure while looking sound from the ground. They wear in step with the springs, which is why replacing both at once is usually cheaper than two separate visits.

A snapped cable lets one side of the door drop and typically pulls it off the track. The bottom bracket a cable attaches to is under full spring tension and must never be unbolted by a homeowner.

Cables are worth inspecting from the ground twice a year and it takes seconds. With the door closed, look at the bottom two feet of cable on each side for kinks, rust or loose strands standing away from the bundle. Any of those means it should be replaced now rather than after it lets go. If one cable has already snapped, do not run the opener: the door is being lifted unevenly, and that is how a bent track and a jammed door get added to the bill.

Each cable winds onto a grooved drum at its end of the torsion shaft, and the two must be set to equal length. If one cable is even slightly longer, the door lifts unevenly, rides crooked in the tracks and wears the rollers on one side — the usual first symptom is a door that looks visibly out of square when it is halfway up. A cable that has jumped out of its drum groove produces the same picture and needs the tension released before it can be re-seated, which is why a crooked door is a call-out rather than an adjustment you can make from a stepladder. Stop using the opener as soon as you notice it, because every further cycle drags the door further out of square and risks turning a cable job into a track and panel job.

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