Snapped Garage Door Cable Repair and Replacement

Where garage door cables actually fail

The lift cables are 3mm to 5mm galvanised steel wire running from the bottom bracket of the door up to a grooved drum on the spring shaft. They take the full weight of the door. Two places wear: the bottom, where water sits in the bracket and rusts the strands, and the drum, where a misaligned wrap saws the cable against itself.

Failure is progressive rather than sudden. Strands break one at a time and stick out as sharp fish-hooks, then the remaining wire lets go under load. Because only one side goes, that corner drops and the door immediately racks in the tracks.

Coastal suburbs and homes where the floor slopes water back into the garage see cables fail years earlier than average. If you hose your garage out, look at the bottom 300mm of both cables twice a year.

Drum alignment is half the job

Replacing a cable without correcting the drums simply repeats the failure. Both drums must sit at the same position along the shaft, both cables need identical tension with the door down, and each wrap has to seat in its groove without crossing over itself.

On site that means clamping the door, releasing spring tension in a controlled way, resetting both drums against the shaft collars, running the new cables and then re-tensioning. We confirm the door lifts square by measuring the side gaps at three heights.

If the cable jumped the drum because the door closed onto an obstruction, we look for that too. A bin, a step or a raised floor edge under one corner is a common cause and easily missed.

Garage door lift cable replacement, and why it is always a pair

Garage door cable replacement is done as a matched pair. The surviving one has done the same number of cycles in the same conditions and is usually part-worn, and mixing an old cable with a new one gives you uneven stretch and a crooked door within weeks.

While the drums are off we inspect the shaft, the end bearings and the bottom brackets. Corroded bottom brackets are common on doors that get washed down, and a bracket letting go under load is worse than a cable failing.

Most cable jobs take 45 to 90 minutes, including resetting the opener limits, which will always be out once the door sits square again. We finish by cycling the door by hand with the motor released, checking it stays put at half height, then running it twice under power to confirm both cables stay seated in their grooves.

• Both cables replaced, never just the broken one
• Drums reset against the shaft collars and tensioned evenly
• Bottom brackets and end bearings inspected for corrosion