Use a screwdriver to fasten the door panel roller brackets onto both sides of the garage door. If you are installing a multiple panel door, place the bottom panel in the threshold area, which is the flooring surface. Attach the hinges, handle and rollers to the bottom panel with a screwdriver or wrench if applicable. Add the hinges, handle and rollers to complete the installation of all of the door panels.
Place the side roller track on the right side and fit it over the rollers. Put a 3/4-inch spacer block between the track and the door to space out the track. Use a hammer to tack 1-inch nails in place temporarily so you can install the lag screws. Drill lag screws into the jamb to attach the track permanently. Repeat this process on the left side of the garage door.
Use a screwdriver to attach the bolts for the top, horizontal track piece to the side track. Use a level to check that the track is straight. Use an open-end wrench to install lag screws to attach the rear track bracket to the nearest roof truss member.
Lift up the garage door 4 feet with the help of a few friends. Use a pair of locking pliers to clamp down the door and hold it in place. Measure the gap between the door panel and the top track. The gap should be 3/4-inch. Adjust the horizontal track for any variance, if needed, so the gap is 3/4-inch.
Connect the side mount extension springs to the rear bracket of the garage door with the open-end wrench. Attach the front brackets that support the pulleys and cables for the side mount springs.
Attach the cable anchor to the roller bracket at the bottom of the garage door panel on the right. Feed the cable anchor through the pulleys attached to the spring on the right side and fasten the cable to the front bracket. Leave 2 to 4 inches of slack in the cable. Run the safety cable through the side mount springs and attach it to the front and rear brackets. Repeat for the left side of the garage door.
Examine the top roller hinges to check that they are straight. Adjust them if needed. Tighten the hinges on the left and right sides to secure the door to the frame.
Test the door's operation. If it is not closing properly, adjust the tension on the extension spring. To reduce tension, move the cable closer to the spring. To increase tension, move the cable away from the spring.
Install exterior doorstops once you are satisfied with the tension on the side-mounted extension springs for the garage door.