Cable Drums: Why One Side of Your Door Lifts Higher

If your door closes with one corner touching down first, or hangs visibly crooked when it's partway up, the cause is almost always at the cable drums.

What a cable drum does

On a torsion spring system, a grooved drum sits at each end of the torsion shaft above the door. The lifting cable runs from the bottom bracket of the door up to its drum and winds into the grooves as the spring turns the shaft.

The two drums have to spool their cables at the same rate for the door to stay level. If one side takes up more cable than the other, that corner rises faster and the door goes out of square.

What goes wrong

A cable comes off the drum. The most common failure. If the door is lowered onto an obstruction, or the door lands hard, the cable can go slack and jump out of the grooves. When the door is raised again, that cable no longer spools properly and the door lifts crooked.

Uneven cable tension. If the cables weren't set to the same tension at installation, or one has stretched, the door will run out of level.

A worn or damaged drum. Grooves wear, or a drum gets damaged in a cable failure. A damaged drum won't spool cleanly regardless of how the cable is set.

A loose set screw. Drums are locked to the shaft by set screws. If one loosens, that drum slips relative to the shaft and the door goes out of level, sometimes progressively over days.

A broken cable. One side loses all lift, that corner drops, and the door twists in the tracks — often bending track and damaging the section.

The symptoms

• One corner touches the floor before the other
• The door hangs visibly crooked when partway up
• A gap under one side of the closed door
• A cable hanging loose or slack when the door is closed
• The door binding in the track on one side
• A sudden bang followed by the door dropping on one side

Why this is not a homeowner repair

The drums, the cables and the bottom brackets are all part of a system under full spring tension. Loosening a drum set screw with the spring wound releases that tension violently. Working on the bottom bracket does the same.

Re-spooling a cable correctly also requires unwinding the springs, setting both cables to matched tension, re-winding, and then verifying the door runs level through its full travel. That's the actual work, and it needs winding bars and the knowledge to use them.

This is the category of garage door repair where injuries happen, and we tell people plainly: leave it.

What to do right now if the door is crooked

Stop using the opener. Running a crooked door through a cycle is how track gets bent and sections get damaged, turning a cable job into a much bigger one.

If the door is up and you need the car out, that's fine — get the car out and leave the door where it is. If the door is down, leave it down.

Then call. This is a same-day repair for us and it gets more expensive the longer the door runs damaged.

What gets checked and replaced

When we're in there for a cable or drum problem, we look at:

• Both cables — if one failed, the other is the same age and usually replaced at the same time
• Both drums for wear and damage
• The springs, since a spring problem is often what caused the cable to go slack
• Bearings at the shaft ends
• The bottom brackets
• Track and sections for damage caused while the door was running crooked

Doing all of that in one visit is far cheaper than piecemeal.

Preventing it

• Never lower the door onto anything, and keep the safety reversal working
• Have cables inspected annually — fraying is visible well before a failure
• Address a door that's started running unevenly rather than living with it
• Replace cables when springs are replaced; they're inexpensive and it's the same visit

We handle cables, drums and spring systems across Greeneville, Chuckey, Mosheim and Greene County, usually same day. Call (423) 262-3147.