Lifting Cable

A lifting cable is a multi-strand galvanized steel wire rope, typically 1/8 inch (about 3 mm) in diameter, that serves as the mechanical link between the spring system and the door. One cable runs on each side of the door. The bottom end loops around a pin or clamps onto the bottom bracket at the lowest corner of the door. The cable then runs vertically up the inside of the vertical track and wraps onto the grooved cable drum mounted on the torsion shaft. As the spring releases energy and turns the shaft, the drum rotates and winds the cable onto its grooves, lifting the door.

The cable must be pre-tensioned and seated correctly in the drum groove before the spring is wound. If the cable slips off the drum during operation, the door loses lift on that side and can drop suddenly, which risks injury and door damage.

Construction and sizing:

Most residential lifting cables are made from 7x19 or 7x7 galvanized aircraft-type wire rope, giving them both flexibility and strength. The standard breaking strength for a 1/8-inch 7x19 cable is roughly 2,000 pounds, far more than any residential door requires. The working load per cable in normal use is about 10-15% of that breaking strength.

At the bottom, the cable ends in a small loop secured by a crimped metal ferrule (a cable ferrule) or a swaged fitting. This loop drops over the pin on the bottom bracket. At the drum end, a cable stop fitting prevents the cable from pulling through the drum slot.

Signs of cable wear:

Cables fray from the outside inward as individual strands break. A frayed cable shows visible broken strands, kinking, or a rusty appearance. For example, a cable that has been in service for 10 years on a high-use door may show fraying near the drum where repeated winding cycles cause the most flex stress. Garage door professionals recommend replacing cables at the same time as springs because a broken spring can shock-load the cable and accelerate fraying.

On extension-spring systems, the cable geometry is different: the cable runs from the bottom bracket, up to a sheave (pulley) at the back of the horizontal track, then forward to an anchor at the front. The extension spring's contraction pulls the sheave and the cable along with it to lift the door.