There are two main types of garage door springs. One is the torsion spring and the other is the side-mounted one. I only discuss the adjustment of the torsional type here, as they are the ones that are most commonly used.

Torsion springs are components that bear the whole weight of a garage door. They are fitted in manually operated, as well as electrically operated doors. The whole garage door apparatus is very economically and smartly designed. The torsion springs and all the related apparatus are situated at the top of a garage door. The torsion shaft, powered by the spring, lifts drums, that easily winds cables connected with the doors, at the bottom. This enables the opening and closing of the garage door. There is a lot of tension, buckled inside the spring apparatus, which makes the job a bit dangerous, if instructions are not followed carefully.

Overview of Adjustment Procedure
Now, let me provide you with an overview of spring adjustment. There are some tools, that you'll need, to get the job done. They are:
  • 7/16 Inch Wrench
  • Two 18-inch long Tension Rods (½ inch in diameter)
  • Ladder
Wear safety glasses during execution of the adjustment procedure.

First thing that you should do, is observe the torsion spring and the connected apparatus carefully. Locate a reddish color cone, around the spring. It should be placed on the left hand side of the torsion spring, and placed away from the garage door's center. Take note of the notches and screws that hold the torsion spring in place.

Next, get hold of one of the tension rods and push it into the first notch. This will achieve the objective of holding the cone. It is absolutely necessary that the tension rod is very firmly inside the first notch and it holds the cone tightly. This procedure is a safety measure that prevents the torsion spring from snapping and hitting you in the face, when you loosen screws.

Next, get hold of that 7/16 inch wrench and slowly loosen the two set screws. While doing this, make sure that the tension rod is placed in the notch firmly or else, the spring will snap.

Next, you must place another tension rod inside another notch, on the same cone. Holding the rods, move the cone towards the right side, to tighten or move it, and towards left to loosen it. This is the adjustment part. Once you are done with the adjusting and satisfied with it, remove any one of the rods and let the other one be placed into position. Next, you can tighten the set screws back again, as this will ensure that the new adjustments you make, are retained. Once the screws are totally tightened, the job is done and you can safely remove the other rod too.

Make sure that you make adjustments on both the torsion springs, as unequal settings will hamper the working of the garage door. It is a good idea to have a helper, who can pass the tools to you, while working. Don't go for actually adjusting the springs, until you exactly understand what you are doing.