Each garage door part belongs to one of four systems: counterbalance (springs, drums and cables), track (rollers and hinges), opener (rail, trolley and photo eyes), and the sections and seals outside. Knowing the names speeds every repair conversation: “the cable came off the left drum” beats “something up top snapped.”
Each group below links to the service that fixes it. One warning first: the counterbalance parts store spring energy, and only a trained technician should loosen, adjust or replace them.
Counterbalance: the parts that carry the weight
The counterbalance system is the springs, shaft, drums and cables that hold the door’s weight, leaving the opener a steering job.
Torsion spring. A heavy coiled spring mounted on the shaft over the opening, wound so it turns the shaft as the door rises; doors carry one or two. Why it matters: a broken one opens a gap of a couple of inches between coils, and DASMA’s advice for two-spring doors is to replace the pair even if only one broke. See spring replacement.
Extension spring. A long spring that stretches beside each horizontal track on older or lighter doors and pulls the door up as it contracts. Why it matters: it behaves differently from a torsion spring, as our torsion versus extension springs guide explains.
Safety cable. A slim steel cable passing through the coils of every extension spring, secured to the wall or ceiling at each end. Why it matters: when a spring breaks, the cable keeps its pieces from whipping across the garage, and DASMA wants a door without them inspected.
Torsion tube. The steel shaft, usually a hollow tube, that spans the width of the door and carries the springs and drums. Why it matters: a bent or drifting tube winds the two cables unevenly, and the door starts to rise crooked.
Winding cone. The fitting at each end of a torsion spring. The fixed cone bolts to the center bearing plate; the outer cone has sockets for winding bars and set screws that grip the tube. Why it matters: those set screws hold the spring’s entire wound tension.
Winding bars. Solid steel rods, sized to the cone’s sockets, that a technician uses to add or remove spring tension in small turns. Why it matters: a screwdriver or makeshift bar can slip out of the cone under load and strike hard.
Center bearing plate. The bracket on the wall above the middle of the door that anchors the fixed end of each torsion spring and supports the tube on a bearing. Matching end bearing plates hold each end of the tube. Why it matters: it needs solid framing behind it, because the springs pull on it constantly.
Cable drum. A grooved spool fixed to each end of the torsion tube. Why it matters: the lift cable winds into those grooves, and a drum that slips on the tube or a cable that jumps a groove leaves one side lower. See cable and drum repair.
Lift cable. The braided steel cable from each bottom corner of the door up to a drum, or over pulleys on an extension-spring door. Why it matters: broken strands are a warning, and a cable that lets go drops its side of the door, as described on cable hanging loose.
Bottom bracket. The bracket at each lower corner where the lift cable attaches and the lowest roller rides. Why it matters: it sits under full spring tension, so it must stay bolted while the springs are wound, however rusty it looks.
Track and rollers: the parts that guide the door
The track system steers the door from vertical to horizontal and back, guiding it but carrying none of its weight.
Vertical track. The upright steel channel on either side of the doorway, fastened to the jambs with brackets. Why it matters: its bottom end sits near the wet slab, where rust and bumper strikes do their damage first.
Horizontal track. The channel that curves away from the vertical track and runs back under the ceiling, held up by a rear hanger. Why it matters: a sagging hanger or a kinked curve is where many off-track doors begin. See track repair and off-track door repair.
Roller. A steel or nylon wheel that rides inside the track. Why it matters: worn steel rollers develop flat spots and grow loud, while sealed-bearing nylon rollers stay quieter.
Roller stem. The shaft of the roller, which slides into a hinge or bracket on the edge of the door. Why it matters: a bent stem makes its roller bind or skip, often after the door is hit or forced.
Hinge. The steel hinge joining two sections; hinges at the ends of the door also hold a roller stem. Why it matters: a cracked hinge or stripped screws let a section sag out of line. See roller and hinge replacement.
Hinge number. The number stamped on an end hinge. DASMA’s terminology sheet explains that end hinges are graduated and numbered for correct placement, so the closed door sits flush against the jambs. Why it matters: the wrong number can leave the door rubbing the trim or sealing poorly.
Opener: the parts that move the door
The opener moves an already balanced door along its rail, reversing when it meets an obstruction; it is not built to lift a door the springs have stopped carrying.
Rail. The long beam between the motor unit and the wall above the door, carrying the chain, belt or screw. Why it matters: its length has to suit the door height, and a bent rail makes the trolley bind.
Trolley. The carriage that slides along the rail and connects to the door arm; Linear’s manual calls it the traveler instead. Why it matters: it holds the release mechanism, and a cracked trolley can let the motor run while the door sits still.
Emergency release cord. The red pull handle on the trolley that frees the door from the opener. Why it matters: federal rules require it, and everyone who uses the garage should know where it is before the power fails.
J-arm. The curved half of the door arm, linking the trolley to the bracket on the top section. Why it matters: it and its bracket take the strain, and can bend, when the opener drives into something.
Operator reinforcement bracket. The steel bracket fastened to the top section where the door arm attaches. Why it matters: it spreads the opener’s pull so the top section does not bow or crack. See opener installation.
Drive gear and sprocket. In many chain and belt openers, the motor turns a drive gear, and a sprocket on the same assembly moves the chain or belt. Why it matters: a worn gear lets the motor hum or run without moving the door, a fixable opener repair.
Logic board. The circuit board in the motor unit that reads the controls and sensors and runs the motor, often carrying the radio receiver and learn button too. Why it matters: when every remote quits but the wall button keeps working, the receiver on this board is a suspect.
Photo eyes. The pair of sensors mounted low on both door jambs that aim an invisible beam across the doorway. Why it matters: a blocked or misaligned pair stops normal closing, and DASMA’s guide puts them no higher than 6 inches off the floor. See safety sensor repair.
Sections and seals: the parts you see from outside
The door itself is a stack of hinged sections, edged with seals that keep rain, wind and leaves out of the garage.
Section. One full-width horizontal piece of a sectional door, which DASMA defines as two or more such pieces hinged together. Why it matters: a damaged section can sometimes be replaced alone, as long as a match is still made. See panel and section replacement.
Strut. A horizontal steel stiffener bolted across a section. Why it matters: DASMA’s terminology sheet says it cuts sagging while the door hangs open overhead and raises how much wind the door can take.
Bottom seal. The rubber or vinyl strip along the bottom edge that meets the floor. Why it matters: once it flattens or splits, rain, leaves and mice find their way under the door.
Retainer. The aluminum or steel channel on the bottom edge that holds the bottom seal. Why it matters: seals come in several profiles, so a bent or corroded retainer may need replacing along with the seal. See weather seal and threshold.
Perimeter seal. The flexible strip along the jambs and header, usually a vinyl stop whose soft flap seals against the door face. Why it matters: gaps there let wind-driven rain in along the sides.
Threshold. A rubber strip glued to the slab under the door for the bottom seal to close against. Why it matters: it helps where the driveway slopes toward the garage or the slab has settled.
Quick reference: symptom to part name
A bang points to a spring, a low side to a cable or drum, and a humming motor to the drive gear.
| What you notice | Part to suspect | Where to read more |
|---|---|---|
| A bang, then a door too heavy to lift | Torsion or extension spring | Spring replacement |
| One side low, a cable slack at the corner | Lift cable, cable drum | Cable and drum repair |
| A roller loose from the track, the door crooked | Track, rollers | Off-track door repair |
| A squeal or rumble at the joints | Rollers, hinges | Roller and hinge replacement |
| The motor hums or runs but the door stays put | Drive gear, trolley | Opener repair |
| The door starts down, then reverses | Photo eyes | Safety sensor repair |
| Daylight or water under the door | Bottom seal, retainer, threshold | Weather seal and threshold |
| The top section bent where the opener arm pulls | Reinforcement bracket, strut | Panel and section replacement |
Other names for the same parts
Manuals and parts counters often say torsion shaft, traveler or door arm where this guide says torsion tube, trolley or J-arm.
- Torsion tube: torsion shaft, shaft
- Winding cone: winding plug
- Winding bars: winding rods
- Center bearing plate: center bracket, center bearing bracket
- Safety cable: containment cable
- Trolley: traveler
- J-arm: door arm, curved arm
- Photo eyes: photoelectric sensors, photo beams
- Perimeter seal: stop molding, jamb seal
- Logic board: control board, circuit board
Rollers, seals and cables wear a little every season, and a seasonal maintenance checklist catches most of it while the fix is small.