Garage Door Anatomy, Door Types, and Pre-Job Inspection
Before touching any hardware, a technician must read the door as a balanced mechanical system. A sectional door has four to five hinged panels riding on rollers inside vertical and horizontal tracks, counterbalanced by a spring system. The spring offsets the door's weight (typically 130-350 lbs) so the opener or a person only moves a few pounds. Identify the two spring types: torsion springs mount on a shaft above the header and wind/unwind; extension springs run parallel to the horizontal tracks and stretch. Know the core parts: panels, hinges, end and center bearing plates, the torsion tube/shaft, drums, lift cables, rollers, vertical and horizontal track, and the bottom bracket (which holds cable under full spring tension and must never be loosened with the door under load). Run a standard pre-job inspection: with the door closed, look for frayed cables, gapped or rusted spring coils, cracked hinges, loose lag bolts, and bent track. Perform a balance test by disconnecting the opener and lifting the door halfway by hand. A balanced door stays put; a door that slams down or rises has a spring problem. Check that rollers move freely and the door isn't binding. Measure headroom, backroom, and side room to confirm hardware fits. Photograph existing conditions and note the spring's wire size, inside diameter, and length, plus door height and weight, because every replacement part is sized to those figures. This inspection drives the entire repair plan and the quote.