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How to adjust a garage door spring
Recognize side-mounted extension springs.
There are two kinds of springs your garage door might use: side-mounted extension springs or torsion springs. Before you can adjust the spring on your garage door, you must determine what kind of springs your door has.
Side-mounted springs are easier to adjust, while torsion springs are more dangerous to meddle with, so you would be better off calling a professional if you have these. Side-mounted extension springs run above and parallel to the door track, and they'll have an attached pulley and cable.