How to know your garage door needs spring replacement
The unmistakable signs are a 2 to 4 inch gap in the torsion spring coil above the door, a door that opens 6 to 12 inches and stops, an opener that strains and immediately reverses, or one side of the door hanging visibly lower than the other. You may also see the lift cables hanging loose off the drums.
If your door slams down hard the moment you release it manually, your spring is past its rated life and ready to fail. Don't wait for the bang—replace before it strands you.