Step 1

Disconnect any door opener and position the door half open (you may need a stepladder). It should be level and stay put, and you should be able to raise or lower it from this position with very little coaxing.

Step 2

To adjust the spring tension, open the door fully to relieve all spring tension and clamp a wood block, locking pliers or a similar stop onto the tracks just below the bottom rollers to hold it open.

Step 3

Disconnect the lifting cable from the brace near the bend in the track and move it to a hole closer to or farther from the door to increase or decrease tension. Cables either hook to or tie to a fitting on their end; that fitting in turn hooks into holes in the bracket.

Step 4

Remove the stops, retest and readjust as necessary. Once the door remains level, you must make any further adjustments equally on both sides.

Step 5

If the lifting cable is hooked to the hole closest to the door and still needs more tension, shorten the cable. Disconnect the cable or loosen it enough so you can feed more cable through the fitting. With the cable shortened and securely reattached to the fitting, hook it on the bracket and adjust the tension.

Step 6

If you have shortened the cable to the point where more shortening would create tension with the door in the open position, the springs are worn and need replacing. Springs are rated according to the number of pounds they can properly support, so you need to weigh your door in this case.

Step 1

Raise the door to relieve all tension and block the door open as described in "Test and adjust the tension". If you haven't already done so, move your car out of the garage.

Step 2

Disconnect the safety-cable springs from the track support at the rear of the garage. The cable is usually bolted, so you'll use a wrench to disconnect it; the springs may be attached to a hook or equipped with brackets bolted to the track support.

Step 3

With one person on each side, raise the door a bit to remove the stop blocks and lower it to the floor. Garage doors can weigh hundreds of pounds, so work with a helper. Lift the door and insert a bathroom scale under the center of the door, then lower the door onto the scale.

Step 4

If the door's weight exceeds the capacity of your scale, place the scale inside the door and rest a 2-by-4 on the scale and on a block of wood outside the door. Lower the door onto the 2-by-4 and double the weight measurement to determine the required spring capacity.

Step 1

If you have not already done so, support the door in its open position, remove the safety cable and spring from the rear track support, and disconnect the lifting cable from the bracket as described in "Weigh the door," above.

Step 2

Disassemble and remove the front bracket and clevis-pulley assembly and the rear brackets from the old spring. Reattach them to the new spring.

Step 3

Feed the safety cable through the spring and reattach it to the rear track support with a nut and bolt. Feed the lifting cable through the clevis pulley, reattach it to the fitting, hook it onto the bracket and adjust the tension.