Lift the garage door slowly until it is in the half-open position. If you have a door with stretch springs, have a friend help you lift the door.
Lock the jaws of a pair of vise grips onto the vertical track, with the handles over the top of the bottom roller to prevent the door from raising any higher. If you have a stretch spring door, attach the vise grips below the bottom roller to prevent the door from closing. Repeat for both sides of the door.
Set up your stepladder under the rear end of one of the horizontal tracks. Move the track toward the side of the garage door so that there is a 1/2-inch space between the side of the door and inside of the track.
Find the two joists in the ceiling closest to the end of the horizontal track. Measure between the two joists with a tape measure. Cut a piece of pre-punch angle to the measurement. Attach the pre-punch angle onto the joists with wood lags and a socket on your impact wrench or drill. The angle on the joists should be as close to the end of the track as possible.
Place a torpedo level on the top of the horizontal track. Lift the track and hold it steady when it is level. Measure from the angle on the ceiling to the hole on the back of the track. Cut a piece of angle iron to the measurement.
Position the second piece of angle iron against the outside of the track with one end against the angle iron on the ceiling. The second piece of angle iron should be straight from the ceiling to the track. Insert a bolt through the holes of the two pieces of angle where they join and thread a nut onto the bolt.
Insert a bolt through the hole in the horizontal track and into the second piece of angle iron. Secure the bolt with a nut. Do not tighten the bolts at this time.
Measure from the end of the track to the end of the ceiling angle iron opposite the second piece. This measurement is at an angle to provide a sturdy support. Cut a third piece of angle to the measurement.
Secure one end of the third piece of angle to a hole on the second piece close to the track with a bolt and nut. Secure the other end to the ceiling angle with a bolt and nut. Tighten all nits and bolts with a wrench. Repeat for the opposite side of the door.