The bang, and what just happened
A garage door spring snapping sounds like a gunshot from inside the garage. It is loud enough that people in the house get up to look, and it is followed by a door that will not lift — by hand or by motor — because the spring was the only reason the door was ever light enough to move. A sectional door weighs somewhere between eighty and a hundred and fifty kilograms. The springs carry all of it. When one goes, the motor is suddenly being asked to lift a weight it was never designed for, and it either strains and stops or strips its gear trying.
There are two kinds. Torsion springs sit on a steel shaft above the door, wound tight, and unwind as the door lifts. Extension springs run along the tracks on either side and stretch as the door closes. Torsion springs are on most sectional doors in Cape Town; extension springs are on older doors and many tip-ups. Both fail the same way — metal fatigue after somewhere around ten thousand cycles, which on a family door opening six times a day is about five years — and both are replaced the same way, by someone with the right winding bars and the experience to use them.
Why this is the one job to leave alone
Every other repair on this site is something a competent person could, in principle, attempt themselves and merely do badly. A spring is different. A torsion spring under tension stores enough energy to lift a hundred kilograms a couple of metres, and if that energy is released the wrong way — a bar slipping out of the winding cone, a set screw loosened before the tension is off — it comes out as a steel bar moving faster than a hand can get out of its way. The injuries are broken fingers, broken wrists, and worse. This is not caution for its own sake; it is the one garage door job that genuinely hurts people who try it.
The safe procedure is unremarkable once you know it. The door is fully closed and clamped so it cannot move. The old spring is unwound a quarter turn at a time with two bars, never one. The new spring is matched to the door by weight and height, wound to the correct number of turns, and the door is then balanced — lifted by hand to check it stays put at any height — before the motor is reconnected. A door that has just had its spring replaced and is not balanced afterwards will eat its new motor within the year, so the balance check is the job, not an extra.
One spring or both
Doors with two torsion springs — most double doors, and some heavier singles — should have both replaced when one goes. The two were fitted together, have done the same number of cycles, and are the same age; the surviving one is within weeks of the same failure, and replacing it alone means paying for a second callout for a job that could have been done in the same hour. That is not upselling. It is the same reason a mechanic replaces brake pads in pairs.
Single-spring doors get one spring. Extension-spring doors get both springs replaced as a pair for the same reason, and get safety cables threaded through them at the same time if they do not already have them — an extension spring that snaps without a safety cable becomes a projectile, and a surprising number of older Cape Town doors are running without them.
The spring that has not snapped yet
Springs give notice. A door that has become heavier over a few months, that drifts down when the motor is disengaged, or that the motor now strains to lift, has lost its wind — the spring has fatigued and stretched without breaking. It is still doing part of the job, and the motor is doing the rest, which is why the motor is the thing that fails first on a door with a tired spring.
Rewinding a spring that has not broken is possible and is sometimes the right call on a newer spring. On a spring past a few years old it is a false economy: the fatigue that let it lose its wind will let it snap, and the rewind buys months. Where a door is heavy but the spring is intact, the honest quote is usually a replacement, and the honest explanation is that the motor repair you called about is a symptom of this, not a separate fault.
What is on the van, and how long it takes
Torsion springs are stocked in the common wire gauges and lengths that cover most Cape Town doors, along with the cones, cables and bearings that are replaced at the same time as a matter of course — a spring change that reuses ten-year-old cables and dry bearings is half a job. Most spring replacements are finished in about an hour, including the balance check and the motor reconnection. Where a door needs an unusual spring — a very heavy timber door, a custom-height opening — the measurements are taken on the day, the door is secured, and the spring is fitted on the return.
A snapped spring is treated as an emergency when the door is stuck open, or shut with a car inside, because in the first case the house is exposed and in the second someone cannot get to work. Those go to the front of the queue at any hour through the emergency garage door repair line, at the same rate as a weekday afternoon. Where a door has come off its track in the same failure — common, because a door with one snapped spring lifts crookedly — the cable and track repair is done in the same visit.