Posted June 21st, 2016 at 11:37 am by Dan Musick
There are two types of operators, trolley and drawbar.
On trolley type operators the drawbar arm pushes and pulls the top of the door to open and close it. On jackshaft operators the operator turns the torsion shaft to open and close the door. On this type of operator the cables normally loosen momentarily until the weight of the door pulls on the cables. Sometimes, however, the cables come off the drums when closing the door from the open position.
The best solution to prevent this problem is to pitch the horizontal tracks at least an inch for every foot of track length. This allows the weight of the door to push down into the opening, thereby keeping the cables on the drums tight as the door closes.
When pitching the tracks is neither possible nor feasible, a second solution is to install pusher springs in the backs of the tracks to push the door down from the open position. This has been a helpful solution for many of the residential Liftmaster Model 8500 Openers that turn the torsion shaft to operate the door.
A third option is to install a larger drive sprocket on the end of the torsion shaft. This will reduce the turning speed of the torsion shaft rotation possibly eliminating the possibility of the cables coming loose.
A fourth solution is to install cable keepers. These will pull a few inches of loose cable away from each drum.
A fifth solution from the early years in the trade was to install 12″ of screen door spring, hooking one end to the bottom cable loop. We would stretch the top eight or more inches and secure it to the cable. The spring would pull the slack in the cables to prevent them from coming off the drums.