If your garage door slips down below the header after you have opened it, you garage door springs need to be adjusted. There are two different types of spring systems for garage doors. Torsion springs are mounted directly above the door and need to be wound with special tools. Adjustments to these types of spring should only be done by a professional. Extension springs stretch along the top track on each side. These types of springs can be adjusted by the homeowner.
Raise the garage door up to its fully open position. Secure the garage door in this position by clamping vice grips on the vertical track directly below the bottom panel.
Locate the cable clip that is attached to an s-hook toward the front of the horizontal track. Disconnect the s-hook from the track.
Untie the cable from the cable clip, but do not remove it from the clip. Pull forward on the cable until the spring just begins to resist using one hand. Slide the clip down the cable with the other hand until the front of the clip is about one inch from the last adjusting hole on the track. Hold it there while slowly releasing the tension.
Tie the cable securely to the cable clip and insert the s-hook back into it. Grab the cable again with one hand and pull until you can insert the s-hook back into an adjustment hole on the track.
Repeat the previous steps for the opposite side of the door. The goal is to have the same amount of tension on each side of the door.
Hold the garage door and remove the vise grips from the track after the spring tension has been adjusted. Release your hold on the door and see if it stays up all the way. Slowly close your door about halfway and release it. Ideally, the door should slowly float up from this point.
Close the door completely and release it. The door should stay closed. If it doesn't, make further adjustments. If adjustments cannot fix the issue then replacement springs may be necessary.