Extension Springs on Mount Prospect's Older Single Doors

An extension spring is under tension along its whole length, and it hangs above the horizontal track. In an attached garage that means it hangs directly over the route between the car and the door into the house. When one parts, the loose end goes somewhere, at speed.

A containment cable threaded through the centre of the spring and anchored at both ends turns that into a spring that thrashes and stops. Garages built here in the fifties and sixties frequently never got one, because it was not standard practice at the time and nobody has been under the door with a torch since. Where they are missing, they go in with the new springs as part of the job.

The lift cable on an extension door runs from the bottom bracket, over a pulley at the front of the horizontal track, back along the spring and onto an anchor at the rear. Those pulleys wear. A sleeve bearing that has gone dry stops turning, and once the pulley is static the cable saws across it and starts shedding strands. A new cable on a seized pulley lasts weeks.

The rear anchor loads into a perforated hanger lagged up into the ceiling joists. On a split-level with a room above the garage, that hanger is fixed into the floor structure of whatever is upstairs. A hanger working loose is worth finding before it becomes the reason the spring came adrift, so it gets a hand on it every time we are up there.