Why are my garage door cables loose when the door is fully open?

Some cable slack at full open is normal and expected. When your door rises, the spring releases tension and the cable wraps tightly around the drum, leaving a short loop of slack near the bottom of the door. What is NOT normal is one side looser than the other, a cable that sags off the drum, or a cable pooling on the floor. Those patterns signal a real problem that can make the door unsafe to operate.

Why cables go slack at the fully open position

When your garage door is closed, the torsion spring above the door is fully wound and under high tension. That tension is transferred through the cables, which run from the bottom corners of the door up and around the drums on the torsion bar. As the door rises, the spring unwinds and releases tension progressively. By the time the door is fully open, most of the spring energy has been used and the cables are carrying very little load.

The result is that a fully open door will normally show a small amount of slack cable near the drums or hanging slightly loose near the lower sections. The cable should still be seated in the drum groove and should not sag dramatically or touch the floor. Think of it like a rope used to lift a heavy box: when the box is at the top, the rope goes loose. A small amount of that is normal. A pile of rope on the floor is not.

The drum is designed with a tapered groove so the cable wraps in organized, tight coils as the door rises. When everything is working correctly, that groove holds the cable in place even when there is little tension on it.

One-sided slack: the warning sign that matters most

Symmetric slack at full open is not a reason to call a technician. Asymmetric slack is. If one cable hangs noticeably lower, sags to the side, or shows more looseness than the other, the door is lifting unevenly. That asymmetry points to a specific problem on one side of the system.

The two most common causes of one-sided slack are:

• Unequal spring tension: If one torsion spring has lost more tension than the other over time, or if a single-spring system has stretched unevenly, one cable is doing more work than the other. The side with less spring support shows more slack at the top because the drum on that side is not receiving enough force to pull the cable tight.
• Drum wound differently on each side: If the cable drum on one side is wound with fewer or more coils than the other, the cable lengths do not match. One side runs out of cable before the other, causing visible asymmetry at the top.

Track misalignment is a third cause. If one track is not plumb or is slightly bent, the door drags on one side during the lift, which means the cable on that side handles more load than the geometry intends. The result is uneven drum wear and uneven slack at full open.

Warning signs, root causes, and what the repair involves

Some slack is normal, but these four conditions require you to stop operating the door right away and call a technician:

1. The cable is visibly off the drum. A cable that has jumped the drum groove will coil randomly and the door operates with no cable guidance on that side.
2. The door tilts to one side when opening or closing. This is the door showing you the load is unbalanced.
3. A loud bang preceded the slack. A bang followed by new slack almost always means a spring broke. Stop immediately.
4. Strands of the cable are fraying or broken. The cable is failing and can snap under load.

Operating a door with any of these signs risks a sudden drop of a 150 to 400 lb door. That is an injury risk and a vehicle damage risk. Disconnect the opener and do not use the door manually until a technician inspects it.

Root cause	How to spot it	Repair type
Worn cable in drum groove	Cable visibly seated crooked or bunching	Cable replacement, drum inspection
Imbalanced torsion spring	One side slack, door tilts in tracks	Spring adjustment or replacement
Drum wound differently	Cable lengths differ, asymmetric slack	Drum rewinding, cable re-seating
Track misalignment	Door drags on one side during travel	Track adjustment
Frayed or stretched cable	Visible strand breaks, slack at top	Cable replacement

The repair required depends on what is actually causing the slack. A technician will balance test the door (disconnect the opener and lift manually to mid-height), inspect both drums for even cable coiling, and check the spring for equal tension on both sides. In many cases, a cable that slipped its groove can be re-seated in under an hour. If a spring is the underlying cause, that repair is done at the same visit.

It is also worth knowing that cables wear at the points of greatest bending stress: near the bottom bracket where the cable attaches to the door, and where the cable wraps around the drum. If you inspect the cable and see fraying, rust staining, or kinking at either of those two points, replacement is the right call even if the cable has not yet come off. Waiting until full failure means replacing the cable in an emergency rather than on a planned service visit.

Why you should not adjust cable tension yourself

Cables are connected directly to the torsion spring system. That spring stores hundreds of foot-pounds of energy. Adjusting the drum set-screws or attempting to rewind cable while the spring is still loaded is one of the more dangerous DIY garage door tasks. Even experienced people have been injured when a winding bar or tool slips while under spring load. The standard approach is:

• The door is fully opened to release spring tension.
• Locking pliers are clamped on the track below the lowest roller to hold the door up.
• The opener is unplugged.
• Only then is the drum or cable adjusted.

This is not a task for improvised tools or a single person. A technician does this with the correct winding bars and knows how to assess whether the cable, drum, and spring all need attention or just one component does.

What a technician checks in Denver and the Front Range

Colorado's temperature swings from below-zero winters to hot, dry summers are rough on cables. Road salt tracked in during winter accelerates corrosion on the steel strands. G Brothers technicians check cable condition at every tune-up because fraying often starts near the drum or at the bottom bracket, where the cable bends most sharply, and a frayed cable can look normal from ten feet away.

If your door's cables look loose or uneven at the top, or if you notice the door tilting or jerking during travel, a service call is the right next step. G Brothers offers same-day service across the Denver metro and Front Range, and free estimates on cable and spring repairs. The inspection will tell you whether a simple cable re-seating is all that is needed or whether a spring adjustment is also due.