Garage doors use heavy duty steel springs to counterbalance the weight of the door and make it easier to open and close. Garage doors typically weigh hundreds of pounds and even a small single door can weigh 100 pounds or more.
Without the assistance of springs, it would be very difficult for most people to open the garage door and garage door openers would need much heavier duty motors and gears. With the assistance of properly adjusted springs, a garage door seems almost weightless and is easily opened by hand or by a modest garage door opener.
The two most common types of garage door springs are extension springs and torsion springs. Extension springs are installed parallel to the door tracks and are connected to the door through a system of cables and pulleys. As the door closes, tension is placed on the spring and it extends, bearing most of the weight of the door. The spring contracts as the door opens.
Torsion springs are mounted over the top of the door parallel to the door itself. Unlike extension springs, torsion springs work by coiling and uncoiling as the door opens and closes.
A garage door spring is good for thousands of cycles of opening and closing the door, but the steel in the spring fatigues over time and all garage door springs eventually break. A garage door spring is most likely to break when the door is closed or closing because that is when the greatest amount of tension is put on it. You will hear a loud banging noise when the spring breaks.
Contact a garage door repair service to replace a broken garage door spring. These springs are under a lot of tension and can cause serious injury or even death if they are mishandled. Expect to replace both springs at the same time. If one spring breaks, the other is not far behind and your door will open best with two springs of approximately equal age and strength.
