How do I adjust garage door cable tension?

Cable tension controls how evenly a garage door lifts and how much work the opener motor does. When tension is off, one side of the door carries more load than the other. The door tilts in the tracks, the opener strains, and the cables wear unevenly. The adjustment method depends entirely on which spring system your door uses. For torsion springs, cable tension and spring wind are locked together, making this a professional repair. For extension springs, there is a limited DIY path if you take the right steps first.

How cable tension actually works

The cables on a garage door do not create tension by themselves. They transmit tension from the springs to the door. When the door is closed, the springs are wound or stretched tight, and that stored energy runs through the cables to hold the door's weight. When the door opens, the spring energy unwinds, and the cable unspools from the drum as the door rises.

On a torsion spring system, the cable wraps around a drum mounted on the same shaft as the torsion spring. The drum position and the spring wind work together. If you loosen the drum to add or remove cable, you change the spring's effective torque output at the same time. You cannot cleanly adjust one without accounting for the other. This is why torsion cable tension adjustment is not a safe DIY task for most homeowners.

On an extension spring system, the spring runs along the side tracks and connects to the cable via a pulley. Cable length at the bottom bracket can be adjusted somewhat independently of the spring stretch, which is what makes limited DIY adjustment possible here. Even then, the springs must be fully relaxed before you touch anything, because an extension spring under load can snap the cable and strike with significant force.

The DIY-safe adjustment path for extension spring systems

If your door has extension springs (long springs running parallel to the horizontal tracks on each side), here is the procedure that keeps you on the safe side:

1. Open the door fully. This relaxes the extension springs. Verify they are limp before proceeding.
2. Clamp a pair of locking pliers (Vise-Grips) onto each vertical track just below the lowest roller. This locks the door in the open position so it cannot fall.
3. Unplug the opener.
4. Locate the cable anchor at the bottom corner bracket. The cable passes through a slot or hooks into an eyebolt there. Some systems allow you to move the cable to an alternate hole in the bracket, which shortens or lengthens the effective cable run.
5. Reconnect, remove clamps, and test balance: disconnect the opener trolley, lower the door manually to about 3-4 feet, and let go. The door should stay put within a few inches. If it falls, the cable is too slack. If it rises, the cable is too tight.

Do not attempt this with the door closed or the springs under load. The moment the springs are stretched, the stored energy makes any cable adjustment dangerous.

Why torsion spring cable tension is a professional job

Most residential doors built since the 1990s use torsion springs. If your door has a single horizontal metal rod (the torsion bar) running above the door with a coiled spring on it, you have a torsion system.

Adjusting cable tension on a torsion system requires loosening the drum set screws and moving the cable position. But the drum sits on a shaft that is already loaded with wound spring tension. The moment you loosen the set screw, the shaft can rotate under that stored energy. A torsion spring for a standard two-car door holds roughly 100-200 foot-pounds of torque. If the shaft rotates while your hands are near the drum or winding cones, the result can be severe: broken fingers, a cable whip, or the door dropping suddenly.

Professionals use a specific sequence: release some spring tension first by unwinding a quarter-turn with properly fitted winding bars, then adjust the drum, then rewind the spring to restore balance. Doing this without winding bars or with improvised tools (screwdrivers, rods) is the most common cause of serious garage door injuries.

Spring type	Cable adjustment	Who should do it
Torsion (coil over door)	Requires spring rewind	Professional only
Extension (runs along tracks)	Limited bracket adjustment possible	DIY if springs are relaxed

How to tell if cable tension is actually the problem

Before attempting any adjustment, confirm that cable tension is what is wrong. Several related problems look similar:

One side hangs lower than the other. This is the classic cable tension imbalance sign. But also check whether a cable has actually slipped off the drum groove, which requires the cable to be reseated rather than just tensioned.

Opener strains or the door feels heavy. More often this is a spring problem than a cable problem. The cable transmits spring force; if the spring has lost tension or broken, no cable adjustment will fix the door's heavy feel.

Door tilts in the tracks. Binding in the tracks themselves can mimic this symptom. Clean the tracks and check for bent sections before assuming the cables are at fault.

Loose cable when the door is fully open. A small amount of cable slack at full open is normal. The cable unspools from the drum as the door rises. The cable should never sag off the drum or pool on the floor, but a few inches of drape in the cable at the top of travel is expected. If the cable is hanging completely slack or has come off the drum on one side, that is a different problem from tension adjustment: the cable needs to be reseated in its drum groove, which is a professional repair on a torsion system.

Cable on only one side seems too tight or too loose compared to the other. Asymmetric tension is the most common real-world cable complaint. It almost always points to a spring that has lost tension on one side or a drum that wound differently during a previous adjustment. Trying to equalize the cables by pulling one tighter without addressing the spring imbalance will not hold: the root cause is the spring, not the cable itself. A tech will check both cable positions and both spring tensions at the same time.

When to call a professional

Call a garage door technician for any cable adjustment on a torsion spring system, for any cable that has come off the drum, for frayed or broken cables, and for any situation where the door is tilting, binding, or falling during operation. Do not try to run the opener to force the door if cables are visibly slack or asymmetric. A broken cable is a same-day repair: the door is unsafe to use until it is fixed, and attempting to drive through the doorway with a broken cable risks the door dropping on a vehicle. G Brothers serves Denver and the Front Range with same-day cable and spring service and free estimates. We carry cables and drums for all major door brands and can diagnose cable tension problems alongside any related spring issues in a single visit.