Overhead garage doors because they usually span a distance of eight to sixteen feet sometimes sag, especially when they are regularly left open for long periods of time.
Most modern garage doors have two special parallel metal bracing rods that are mounted at the top and bottom of the door on the inside. They reduce sagging, but don't always entirely prevent it.
Each brace consists of three mounting brackets and a steel rod that's threaded at both ends. A door kit contains six brackets and two rods. The end brackets for the rods two for each rod are mounted at each corner of the door, and the remaining two brackets are mounted on center between each pair of end brackets, one at top center and one at bottom center.
Once all six brackets are bolted in place, the long flexible rods are fed through their respective end brackets, and the center of each rod rests in a slot in its own center bracket. Nuts are placed on the ends of the rods and are tightened. (Flat and lock washers should also be used). Since the middle bracket is longer than the end brackets, pressure is exerted at the middle of the door as tension is increased at the ends of each rod. The tension increases as the nuts are tightened. Thus, the rod can transform a curved door into a straight one.
If you view the garage door from either the top or bottom edge with the bracket in place you will notice that the frame of the door and the rod and the brackets create two long narrow triangular shapes. A triangle is one of the strongest structural configurations known to man.
If you have brackets on your garage door and the door is sagging, all you need to do is tighten the nuts at the ends of both rods to straighten the door.
If your sagging door has no rods, rods should be installed and adjusted.
This is definitely a do-it-yourself project. You'll need a bracket kit, a drill, a measuring tape, a hammer and nail set or a nail, a pencil and a small wrench.
First, with the overhead-door closed, from the inside, align the brackets and mark, and drill the holes all the way through the door. When you are drilling through wood, follow this procedure for best results:
After the holes are pencil-marked and before drilling begins, use a nail set or a nail to make a pilot hole. Drill until the bit barely begins to penetrate the opposite surface, then immediately stop drilling.
Go to the other side of the door and finish the holes. Following this procedure will result in sharp, clean holes. Not doing so might tear the surface when the bit comes through.
Use carriage bolts to mount the brackets. The carriage bolt head looks like a rivet from the outside and gives a neat, clean appearance. Remember, use bolts not screws. As years go by, there is the chance screws would come loose.
Over-tightening the tension rod will cause the door to bulge in the opposite direction. If this happens, simply release the tension on the rod by loosening the nuts at the ends of the rods.
This is a $30 job that eventually could save you from replacing your garage door.