Garage door cables almost never fail without notice. Weeks or months before one lets go, it starts shedding wire strands — a few fine metal whiskers that catch a rag, a rust-coloured smear on the drum, a faint clicking as the door rises. Most people never look, because the cables sit at the far left and right of the opening where nothing else usually needs attention.

Then one morning the door comes down crooked, one side drops faster than the other, and the panel wedges in the opening. At that point the cable is the visible casualty, but it is rarely the cause.

What the cables are actually doing

On a torsion-spring door, the springs sit on a shaft above the opening. At each end of that shaft is a grooved drum. A steel cable runs from the bottom bracket of the door, straight up the side, and wraps into the grooves of the drum. When the spring unwinds, the drums turn and the cable lifts the door. The cable carries the full weight of the door in tension.

That matters for two reasons. First, the cable is a lifting component, not a guide — so a frayed cable is a load-bearing part that is partway to failing. Second, because the two cables share the load evenly, one failing cable immediately dumps the whole weight of the door onto the other side, which is why the door racks and jams rather than simply dropping.

Why cables fray

Water at the bottom bracket

The single most common cause in a Canadian garage is moisture sitting where the cable loops into the bottom bracket. Snow melts off a car, the water runs to the low corner of the slab, and the cable’s lowest few inches spend the winter wet. Rust forms inside the strands where nobody can see it, the wire loses flexibility, and the strands start breaking one at a time as they bend around the drum.

A drum that is off-centre or loose

If a drum has slipped on the shaft, or one of its set screws has worked loose, the cable stops feeding cleanly into the groove. It rides up onto the flange, doubles over itself, or rubs the drum edge. The wear this produces is localised — you will see a chewed section a few inches long rather than general fuzziness — and new cable installed without fixing the drum wears out the same way.

Unequal spring tension

Springs that have drifted out of balance make one drum do more work than the other. The overloaded cable stretches, the door runs slightly out of level, and the low corner starts to catch the track. This is where cable work and spring repair stop being separate jobs — replacing one without checking the other is how a door comes back for a second visit.

The door hitting something

Closing onto a bike, a bin or a snowbank slackens the cable for a moment. Slack cable jumps out of the drum groove, and when tension returns it is pinched or kinked. Anyone who has reversed into a partly closed door has probably shortened the life of both cables.

Reading the damage

You can learn a lot in sixty seconds with the door fully closed, which is when the cables are under the least tension.

• Fuzzy along its whole length: age and corrosion. Both cables are near the end of their life, not just the one you noticed.
• Chewed in one short section: a drum or pulley problem. The cable is a symptom.
• Kinked or flattened: the cable came off the drum at some point. Expect it to happen again unless the reason is found.
• Rust only at the very bottom: standing water. Worth fixing the drainage, not just the cable.
• One cable slack while the other is tight: stop. The door is already unbalanced.

Why this is not a DIY job

To change a cable you have to unload the springs, and a wound torsion spring holds enough energy to break bones. The cable itself is cheap; the winding cones and the shaft are what make the job specialist work. This is the part of garage door cable repair where the honest advice is to keep the door closed and leave it alone until a technician is on site.

What happens if you keep using it

People do, because the door still mostly works. Three things follow, in order.

The remaining cable takes more load and begins fraying faster. The door runs out of level, so the rollers bind in the tracks and the top section starts to twist. And the opener — which was never designed to lift the door’s weight, only to overcome its friction — starts straining against a door that is no longer balanced. That is how a snapped cable turns into a stripped gear or a burnt-out motor, and why the opener is often the second thing to fail.

The safety-reverse logic makes this worse, not better. When a door binds, the opener reads the extra resistance as an obstruction, reverses, and tries again. Each cycle adds load. A door that reverses partway down is telling you something mechanical is wrong, not that the opener needs adjusting.

Preventing the next one

Cables are wear parts, but their life depends mostly on water and alignment. Keep the bottom corners of the slab dry and clear of snow so the cable ends are not standing in meltwater. Do not spray oil into the drums; it collects grit. Look at both cables twice a year with the door closed, running a gloved hand along them — snags are easier to feel than to see.

And when one cable is replaced, replace both. They have done the same work for the same number of years, and the cost difference is small compared to a second call-out a few months later.

FAQ

How long should garage door cables last?

It depends far more on moisture and alignment than on age or cycle count. Cables in a dry garage with true drums often outlast the springs; cables sitting in winter meltwater can go in a few seasons.

My door closes but one side lands first — is that the cable?

Often yes, a stretched or slipping cable on the low side. It can also be a drum that has moved. Either way the door is unbalanced and the tracks are taking load they should not.

Can I use the opener until it is repaired?

No. Disconnect the opener with the emergency release and leave the door closed. Cycling a door with a failing cable is how the panels get damaged.

Does a snapped cable mean the springs are also done?

Not necessarily, but they are checked at the same time. A cable that broke because of uneven spring tension will break again if the springs are left as they are.