Extension springs stretch above each horizontal track and hold the most energy when the door is closed, and a safety cable is the one part that keeps a broken spring where it is. If yours have none, we fit them with extension spring replacement or on their own, and a door whose springs and pulleys are also worn is worth pricing for conversion to torsion.
Our torsion versus extension guide compares the two spring systems. This page stays with the cable: what the industry says about it, how to spot one, what goes wrong without it, and the pulleys that wear around it.
What a safety cable does, in the industry’s words
A safety cable contains a broken extension spring: DASMA’s glossary defines a containment cable as one threaded through an extension spring to retain the spring if it breaks.
DASMA’s safety tips give the reason plainly. With the door down, extension springs are under high tension, a breaking spring can injure someone, and a cable through the spring, secured at each end to the wall or ceiling, keeps the broken spring contained. Wikipedia’s garage door article adds that the cable also limits the hazard when a pulley or lift cable fails under tension.
Door makers say the same in their own literature. Clopay’s commercial installation manual says an extension spring door must never be operated without a properly installed containment cable, and its homeowner buying guide describes cables running through the center of each spring, anchored to the wall or ceiling.
The standard behind it
The industry standard for counterbalance hardware on home sectional doors, ANSI/DASMA 103, says a counterbalance spring shall be restrained on the inside or the outside.
Its test for an extension spring restraint is blunt. Three samples are cycled at the spring’s maximum design load for one and a half times its rated cycles. Then each spring is stretched until it is destroyed, and the device has to hold the spring, its end loops and the pulleys all three times.
Torsion springs need no such cable. DASMA’s inspection checklist notes that a spring mounted on a shaft is contained by the shaft itself.
How to tell from the floor whether your door has them
With the door closed, a safety cable shows as a thin steel line running straight through the middle of each spring, from a support behind the spring to a bracket near the front of the track.
DASMA’s checklist for homeowners and inspectors asks whether the counterbalance springs and their attachment parts are restrained by a cable or a shaft. Five steps answer it without touching anything.
- Close the door and leave it closed. DASMA’s check is made with the door fully down, which is also when the springs are stretched hardest, so look from the doorway or a side wall rather than from under the track.
- Find the spring above each horizontal track. It runs front to back, hooked to a hanger or framing at the back end, with a pulley in a fork at the front end.
- Look down the middle of the coils. A cable visible inside the spring from end to end is a safety cable. A spring with daylight through its center has none.
- Follow the cable to both anchors. At the back it loops over the support behind the spring, and at the front it bolts to a bracket near the front of the track. It should be fairly tight, though a little slack is fine.
- Photograph both sides. Use your phone’s zoom from where you stand, and include a shot of each pulley.
One fault worth spotting is a cable that leaves the spring through the coils instead of running out of its end. A spring supplier warns that a cable routed that way pinches and wears early, and can damage the spring and the pulley.
What happens when a spring breaks without one
Without a safety cable, a breaking extension spring releases its stored stretch with nothing to stop it, so the broken coil, its hook and sometimes the pulley can fly across the garage.
That stretch peaks with the door closed and a car parked beneath the tracks. A spring supplier describes broken extension springs as tending to explode everywhere, and its standing advice is to stay out of their path whenever the door is closed or moving.
After a break, the door is out of balance and heavy on the broken side. Leave the opener off, do not lift the door by hand, and keep everyone clear of it; DASMA’s checklist says a door with a broken spring should not be operated until the spring is replaced.
Extension springs are not only an old house part. Kelso and Longview have the oldest housing in our area, with median build years in the 1960s, and a light door of that age may well still hang on side springs.
Clopay also says its retail single-car doors 10 feet wide and under generally ship with extension springs, so a store-bought single in a newer Ridgefield or Battle Ground subdivision can carry them too.
Pulleys and sheaves: the parts that wear around the spring
An extension spring door runs its lift cables over four pulleys, two on each side, and those pulleys wear out alongside the springs.
DASMA’s glossary calls them sheaves, metal or plastic pulleys that guide the cables in a counterbalance system. It also names the parts around them: the sheave fork that joins a pulley to the spring, the S-hook, and the back hang that carries the end of the horizontal track.
| Part | Where it sits | What wear looks like from the floor |
|---|---|---|
| Spring pulley | In a fork on the front end of each spring | Wobbles, squeals, or scrapes the track angle as the door moves |
| Front pulley | On a bracket near the front of the horizontal track | A body split where its rivets let go, or a cable riding out of its groove |
| Sheave fork and S-hook | Joining the pulley to the spring, and the spring’s back end to its anchor | A hook bent open, or bright rub marks where metal meets metal |
| Lift cable | Over both pulleys, from a clip on the track to the bottom bracket | Frayed strands where a seized pulley dragged it |
| Safety cable | Through each spring, anchored behind it and at the front bracket | Missing, slack, or routed out through the coils |
A spring supplier names worn pulleys as one major cause of failure on these doors: the ball bearings break down and the pulley scrapes the track angle, or its rivets fail and it splits. The signs it lists are a door that opens partway and stops, closes partway and reverses, binds or scrapes, and sometimes a frayed cable or a dangling spring.
Because the four pulleys share the same miles, that supplier recommends replacing them as a set, and we do the same once one has failed. A dragging pulley also chews the lift cable riding over it, which is why our lift cable guide and this one point at each other.
Safety cable as the stopgap, conversion as the fix
A safety cable makes a broken extension spring far less dangerous, but it does nothing to keep the spring from breaking, so it is the stopgap when the rest of the side-spring hardware is tired.
Fitting cables makes sense when the springs are sound and the door is staying: on a lighter door with good pulleys, cables through a healthy pair close the gap in the system. When the springs are near the end, the pulleys are worn and the cables are missing, the money goes further on a torsion conversion, which removes the springs, pulleys and both kinds of side cable at once.
Torsion hardware is also the starting point for a wall-mount opener, which turns the shaft itself, though the door maker’s provisions for keeping the cables taut still apply. Our conversion page explains the headroom and header checks that come first.
Whichever way you go, the springs are let down before anything is unhooked. Side springs lose their stretch when the door is raised and clamped in its track; nobody unhooks one under load, and the bottom brackets keep their bolts until the cables hang slack. That work, like winding any spring, belongs to a trained technician.