The cables that carry the door — and why they fail
Two steel cables run from the bottom corners of the door up to drums on the spring shaft, and every lift and lower runs over them. In humid, salty air the strands corrode from the inside, fray at the bottom bracket, and eventually snap — often right after a spring breaks and dumps the whole load onto them. A door with one dead cable hangs crooked in the opening, jams against the track, and can drop suddenly, so it should not be operated at all.

