Compact counterbalancing system for sectional doors

A counterbalancing mechanism for a door movable between a closed position proximate a door frame and an open position displaced therefrom comprising, a pair of drum means for reeving lengths of cable thereabout which are affixed to the door, each of said drum means having a non-circular bore, a pair of shaft means each freely rotatably mounting one of said drum means thereon, a pair of bracket means mounted in spaced relation on the door frame, each of said bracket means supporting one of said pair of shaft means, drive tube means having a non-circular cross section extending between said pair of drum means and engaging said bore of each of said drum means for rotating said drum means with said drive tube means while permitting axial movement of said drive tube means relative to said drum means, coil spring means positioned interiorly of said drive tube means, spring perch means in said drive tube means having a non-circular cross section inner engaging said non-circular cross section of said drive tube means for applying rotational forces to said drive tube means while permitting relative axial movement, said coil spring means having one end thereof non-rotatably affixed to said spring perch means and the other end non-rotatably affixed to said shaft means, and means normally restraining said shaft means against rotation and effecting rotation of said shaft means to selectively adjust the torsional forces in said coil spring means.