A torsion spring door hangs from two lift cables, one at each bottom corner, and those two cables carry the springs’ pull down to the door. When one frays, slips off its drum or snaps, the repair is a new pair on our garage door cable replacement page; this guide explains the cable itself.
Cable, drum and bottom bracket each carry spring tension, so looking and photographing from the floor is the homeowner’s part, and touching, loosening or rewinding any of it is ours.
What a garage door lift cable is made of
A lift cable is galvanized steel wire rope, which DASMA’s glossary calls aircraft-type cable: several strands of galvanized wire braided together into one line.
Suppliers write the usual garage door construction as 7x19, meaning seven strands with 19 fine wires in each, and one parts listing also carries a 7x7 cable with seven wires to a strand. Galvanizing coats the wire in zinc against rust, which earns its keep where Pearson Field logs measurable rain on 19 or 20 days a month from November through January.
Lift cable sizes and the drums that take them
Assembled cables sold for 7 and 8 foot residential doors come in 3/32 inch and 1/8 inch, and heavier doors on larger drums step up to 5/32, 3/16 and 1/4 inch cable.
| Cable | Break strength in one supplier’s listing | Where it is used | Drums rated for it in one maker’s catalog |
|---|---|---|---|
| 3/32 in., 7x19 | 1,000 lb | Assembled cables for 7 foot torsion doors | Standard lift drums that take up to 1/8 inch |
| 1/8 in., 7x7 | 1,700 lb | Listed for torsion and extension spring doors | The same 1/8 inch drums |
| 1/8 in., 7x19 | 2,000 lb | Assembled cables for 7 and 8 foot doors | D300-112, D300-144 and D400-96 standard lift drums |
| 5/32 in., 7x19 | 2,800 lb | Taller or heavier residential doors | D400-123 and D400-144, for doors to about 10 and 12 feet, and the D400-54 high lift drum |
| 3/16 in., 7x19 | 4,200 lb | Heavy doors on 5 1/4 inch drums | D525-216, for doors to about 19 feet, plus two high lift drums |
| 1/4 in., 7x19 | 7,000 lb | Commercial heights and weights | D800-384 and the largest high lift and vertical lift drums |
Those figures are the loads at which new cable breaks, not loads it should carry every day, and no supplier we read publishes a working load or a chart matching cable size to door weight. What the drum catalog does show is the pattern: heavier doors ride on larger drums, and larger drums accept heavier cable.
So a replacement pair is matched to the drums already on the shaft and to the cable that came off, never picked from a size printed on a box.
How long a garage door lift cable should be
A lift cable is cut longer than the door is tall, because it has to reach from the bottom bracket up to the drum and still leave wraps on the drum when the door is closed.
One supplier’s assembled cables run 8 feet 6 inches for a 7 foot door and 9 feet 6 inches for an 8 foot door, about 18 inches more than the door’s height. Its custom lengths go out to 18 feet 6 inches for taller openings.
A drum maker’s catalog states the rule behind those numbers. Measure from the cable’s attachment point on the door to the center line of the shaft, then add an allowance from its table, about 8 inches on most of its 4 inch drums. The same catalog requires at least half a turn of inactive wrap on every drum, for safety.
A cable cut too short leaves less than that safety wrap on the drum with the door down, even when it looks long enough. On a high lift door the cable runs longer again, and our high lift guide covers where it should meet the drum.
The fittings at each end of the cable
A lift cable ends in a loop at the bottom and a swaged stop at the top, and each end has its own job.
At the bottom bracket
The bottom end is formed into a loop, held by a ferrule or a two-hole sleeve crushed onto the cable. That loop drops over a pin on the bottom bracket, which DASMA’s glossary describes as a clevis pin secured with a cotter pin.
The bracket can sit two ways. On an inside hook-up the cable runs up between the door and the vertical track, and on an outside hook-up it runs outside the tracks, which changes the bracket and the cable path a replacement needs.
At the drum
The top end carries a cable stop, a swaged fitting that DASMA says keeps the cable from slipping through a slot in the drum. The stop seats in that slot, and on some drums a set screw also clamps the cable to fix its working length.
On extension spring doors
Doors on side springs use lift cable differently. It runs over a pulley on the spring, then over a second pulley at the front of the track and down to the door’s lower corner, and its fixed end hooks to a three-hole clip that sets its length. The cable threaded through the middle of each spring is a separate part, covered in our extension spring safety cable guide.
How a lift cable wraps the drum
As the door rises, each drum turns with the shaft and winds its cable into the grooves, one wrap beside the last, so both bottom corners climb at the same rate.
On standard lift track the drum is flat across its grooves, so the cable pulls with the same leverage from the floor to the top. High lift and vertical lift drums change their radius along the way, which is how they keep a raised or upright door balanced.
The number cast after the dash on a standard drum tracks door height in inches, so one maker’s D400-96 suits doors to about 8 feet and its D400-144 doors to about 12. Other foundries cast other names on the same size, so we read the drum before ordering.
Wayne Dalton’s spring instructions say cable tension must be equal on both sides before the springs are fully wound, and Clopay’s tell installers to keep the cable in the drum grooves. When one side wraps loose, skips a groove or stacks a wrap on another, that corner lags and the door rises out of square.
DASMA also notes that an opener’s entrapment protection, the photo eyes and auto-reverse, does nothing to keep a lift cable seated on its drum.
Putting a wandering cable back in its grooves means taking the spring tension off first. Winding or unwinding a torsion spring, whether it sits open on the shaft or sealed in a tube, is work for a trained technician with proper bars or the system’s own winder, never a homeowner’s fix.
Why the bottom bracket is the end to leave alone
The bottom bracket holds the cable against the full pull of the springs, so it is under load whenever the springs are wound, even with the door closed and still.
DASMA’s safety tips say these brackets are under extreme tension, that nobody but a trained door systems technician should adjust or loosen them, and that many makers now fit tamper resistant hardware so a novice cannot loosen them. Clopay’s commercial manual warns that a loosened corner bracket can spring out with dangerous force.
The industry standard that covers these parts, ANSI/DASMA 103, gives door makers three ways to protect them. Fasteners can be built so they cannot come out by accident while tension remains, made to need special knowledge or a special tool, or painted red with warning labels at the bottom corners.
A red bolt or a warning decal at a corner is that message in hardware. Leave it, and any red bolts on the center bearing plate, alone while the springs are wound.
Four ways a lift cable fails, and what each looks like
Lift cables fail by fraying, rusting, coming off the drum or wrapping unevenly, and each failure leaves a sign you can see from the floor.
- Fraying at the bottom bracket. Broken wires bristle from the cable near the loop, or the cable looks thin and fuzzy just above the bracket. DASMA’s safety tips warn that a frayed or worn cable is in danger of breaking and should be replaced only by a trained technician.
- Rust in a damp garage. The strands turn orange or brown, often with a rust stain on the bracket beneath. DASMA notes that rain getting past the bottom edge of a sectional door is common, and the corners are where it sits; Battle Ground’s NOAA normal runs nearly 15 inches a year wetter than Pearson Field’s in Vancouver.
- Off the drum. The cable hangs in loose loops beside the track or has spilled over the drum’s edge, and the door sits crooked. Slack causes it: a door closing onto ice or a bin, a roller binding on one side, or a spring that broke and shifted the load at once.
- Uneven wrap. No cable is broken, but the door lifts one side ahead of the other, shudders at the same point each trip, or closes with a gap under one corner. A cable is riding loose in its grooves, or a drum has slipped on the shaft.
Any of the four can arrive with a broken spring. If you heard a bang and the door now feels like dead weight, leave the opener unplugged and keep your hands off the door; with its counterbalance gone, the door’s whole weight is free to drop.
Our cable hanging loose page covers what to do while you wait, and a photo of the drum and the bottom corner tells us which of the four it is.