'Adjusting Extension Springs' can be done in two ways. One is by moving the hook that holds the cable to another hole to decrease or increase the tension. The other is by loosening the clamp on the cable and adjusting the length of the cable.
What is the door doing? Is there a gap along the floor when it is closed. Too much tension on the springs. Is the gap on one side only. The springs are not balanced and the side where the gap occurs needs to be adjusted.
Garage doors are heavy and can be dangerous of they are not controlled. A garage door that is not attached to the springs can fall and cause injury. See below to make sure the door is secured before you work on it.
Brace Door Before Adjusting Extension Springs
To be able to adjust the springs, the door must be in a position that release the tension on the springs. For extension springs this is in the up position. To keep the door from falling, it must be clamped to hold it in place.
Raise the door and release the garage door opener. Push the door up as far as you can to release the tension on the springs. Use two pair of vice grips or two C clamps to clamp the track below the roller. You don't want the door coming down while you are working on it. Try tugging on the door to make sure the clamps are tight.
To lower the tension on the spring you want to move the hook one hole away from the door frame, toward the inside of the garage. This will reduce the length of the spring when it is stretched. By doing this you will lower the tension on the spring when the door is down.
This should allow the door to close and not leave a gap. Try adjusting it one hole at a time until it closes properly. Is the gap gone? No, keep trying one hole at a time. Yes, your attempt at adjusting garage door springs has been successful. Good job!
For a door that seems hard to lift the opposite would be true. Moving the hook one hole toward the door frame or toward the outside will increase the tension. Again go one hole at a time and try it. Increasing the tension may cause the door not to close all the way.
If you find that one hole is too much, you will have to adjust the cable. Go to Step Two. Adjust it back if this happens and look into getting a garage door opener to do the lifting. See that? Adjusting garage door springs may be as simple as moving the hook from one hole to another.
Did you run out of holes? Or do you need a finer adjustment than the holes are allowing for? Your cable will have a clip with a knot on it or a clamp where the cable attaches to the hook. Loosen the knot or the clamp to adjust the cable. Make the cable longer to reduce the tension and shorter to increase it.
The cable is looped, so if you increase the length about the distance between two holes on the angle, it will yield an adjustment of about half of what moving it from one hole to another would. Is the door working properly now? Yes, then you are done adjusting garage door springs. Go to the next repair on your list.
Extension springs are not that hard to adjust. You mostly have them on smaller doors that are easier to handle. You can see from the above, that there are a couple of ways to adjust them. To get your garage door in tip top shape, you may need to adjust the track and lubricate it. See the articles 'Adjusting Garage Door Track', 'Oiling Garage Door Hinges' and 'Lubricating Garage Door Rollers' for more information.