On a one-piece door the extension springs are a little different and designed specifically for one piece flip up doors. They are becoming less available to the general public.

big hinge levers

The 2 big hinge levers on the left and right hand side of your door are attached to extension springs that stretch out when door is in the closed position. And when the door is opened the strength of the stretched out spring balances the weight of the door

When you open your door, you do not have to use any extra effort. The only hardware on a one piece door is the hinge levers and the springs on either side of door. One piece doors that have low headroom will use a set of horizontal track with a roller on either side of the top of the door. This allows the door to roll straight back without the door making an arc when it operates.

Common extension springs

The most common extension springs for a one piece doors are made by Holmes Co. They have an orange tag on them and the spring size is stamped on this tag. The most common size is 728C. The seven is the coil wire size and the 28 is the length of the spring. Most of the time an average size wood one piece 2 car garage door will have 4 of these springs -two on each side.

If you are going to attempt to change these springs yourself then there are a few things you need to know. Door has to be all the way open and supported with a 2×4 to hold open door while you make spring change. If a hinge has come apart from the wall than do not go near it or try to operate the door. This can cause serious injury.