Cables are cheap parts doing a critical job. They carry the entire weight of the door on a torsion setup, and on an extension-spring door they carry the spring tension as well. They do not stretch — they fray, and a frayed cable eventually lets go without warning. Treating a frayed cable as “monitor it” is the expensive decision.
How lifting cables fail
The visible fraying usually happens at a specific point, and it tells you something about the cause.
- At the drum. A grooved, worn, or mis-sized drum cuts into the cable at the same spot every cycle. Replacing the cable without replacing the drum means the new one gets cut too.
- At the bottom bracket. The cable flexes against the sharp edge of the bracket every cycle, and the crimp or ferrule at the pin wears. This is also where corrosion collects on a door that sits in damp air.
- Over the drum on torsion doors. The portion running up to the drum takes the highest sustained load and will show the fatigue first.
- Uniformly along the length. Less common, and points to a rating or balance problem rather than wear at a single point — a door running out of balance overstresses the cables.
Also worth checking while we are there: the bottom bracket pin, the drum retaining screw, and whether the drums turn freely. A seized drum puts a permanent twist into the cable.
Why a snapped cable is urgent
There is also a subtler risk. Once one cable snaps on a torsion door, the remaining cable and the centre bearing plate take the full load, and the door usually sits crooked. If the door is left like that, the second cable can follow. The safe sequence is to support or secure the door, replace the cables as a set, and re-balance the whole assembly.
If the door is open and you can see a cable hanging loose, do not run the opener. Close it by hand only if you are certain the door is not on an extension spring with a released cable; if there is any doubt, call first.
Cables and springs are usually replaced together
On an extension-spring door the cables and springs are one system. The spring pulls the cable, and the cable pulls the door. Replacing a cable and leaving the original springs means the new cable carries the same old load, often on springs that are near the end of their life anyway.
On a torsion door the cables run to the drums and the springs are separate, so a cable can fail on its own. Even then, if the springs are of similar age, replacing them at the same visit is the sensible call — one lift, one visit, one mobilisation, and a door whose whole balance path is new.
Whichever layout you have, the parts are a matched set: the cable must be rated for the door weight, and the length must suit the drum. Cables are inexpensive; the point is not to economise on the part that is holding the door up.
What gets inspected during a cable repair
- Cable rating and length against the door weight and drum diameter.
- Drums for grooves, cracks, and a free-running bearing. A damaged drum is replaced, not dressed up.
- Bottom brackets for the pin, the crimp, and the flatness of the plate. A bent bracket will cut a new cable.
- Centre bearing plate on torsion doors, since it carries the load when the cables do not.
- Cable drums and the torsion tube for wind-up and straightness.
- Springs for remaining life, because a cable job is the natural moment to notice a tired spring.
- Track and rollers, so the door is actually running straight after the repair.
Related services & problems
These come up often alongside the work described above.