Unmatched or mismatched spring pair: You may find that you have a pair of springs that are different sizes. This mismatch may be a normal application, since the total torque on the torsion shaft is simply the sum of the torque contribution of each spring (indeed, very large doors can be lifted with 4 or more springs along the torsion shaft). The sum of the torque rates determine the lift; and dividing the torque among multiple springs does not change this. Some repair shops even apply mismatched pairs deliberately, since a few stock sizes of springs can be combined to fit a wider range of door weights than only matched pairs. For example, a technician may carry springs in increments of 20 lbs of lift, and when using pairs this allows a 20 lb increment in possible choices instead of 40 lb increments. Or, one spring from a pair may have broken and been replaced with a spring of equal torque rate but different size than the original.
Not only was the upward-lifting garage door and the electric garage door opener invented by Overhead Door Corporation’s founder C.G Johnson in the 1920s, but we also have a tradition in excellence for garage door repair, service and maintenance. Even with the most reliable products problems can arise and when they do it’s important to know who to contact to fix these issues while providing solutions to prevent future complications.
You might be thinking: Aha! Why don't we lift the door, clamp it in place, and install the springs while they are thus safely unwound, rather than deal with all that accumulation of hazardous torque? The answer: At the top-of-travel, the unwound springs are not fully relaxed; they are still clamped to the torsion shaft with a significant stretch along the shaft axis, plus about a half-turn to keep the door snug at the top. This extra length amounts to the stacking of extra turns that accumulate from winding, also termed "spring growth" in the business. In my case this is about 7 turns of 0.2253 wire, or about 2 inches. Stretching the spring that much and clamping it with a half-turn or so of twist is not feasible.
Customers who have purchased this garage door opener for their homes have been mostly satisfied with the performance of it. Many have raved about how quiet it actually is—one said instead of hearing the metal squeak and clank like with their last one, only the sound of the “wooden door being jostled around as it is pulled up and down” is all you hear with this one. Customers were also happy with the features including the automatic closer when you forget to shut it after you go inside. Some had had issues with the manual being hard to understand while installing it themselves. But most were happy with the overall performance.
Thus it is humanly impossible to dodge a falling door. If the spring happens to break when the door is moving up or down somewhere in the middle of travel, as is more likely, then you'll have even less time. Hence it is not prudent to stand or walk beneath a moving garage door. Of course people often do, and the only reason this does not frequently kill people is that springs typically break at the bottom of travel, where they are stressed the most.
Depending on the design, you can know in advance how many turns are going to have to be unwound. Lifting a 7-foot door by winding a cable on a 4-inch diameter (about 1 foot circumference) drum requires about 7 turns, plus one extra turn to maintain cable tension at the top-of-travel. Maintaining tension at the top-of-travel is critical; without it the cable will jump off the drum, requiring a serious repair.
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Cable fail-safe redundancy: Based on the proper setting of the drums on the torsion shaft, the two lift cables divide the lifting force equally to keep the door level as it rises. This not only levels the door, but also provides a fail-safe mechanism. If one of the cables should fail, such as from breaking or losing its end attachment, the other cable will then carry the full weight of the door. This will pull the door up on one side with twice the normal force, while the other side falls from its now unsupported weight, tending to make the door bind in its tracks and jam. Although not foolproof, this is a safety feature of the design which keeps the door from falling catastrophically if a cable were to fail while the door was traveling. The jammed condition also prevents a lowered door from opening with the hazard of a single broken cable, further minimizing the chances of both cables failing. Since if one cable fails the other must sustain the full weight of the door, the cables and attachments are rated many times the normal working load of half the door weight. A proper safety inspection of the door should include a critical look at the cables and their attachments.
Beware of improprer prior installations: Sometimes the existing door installation is not correct, and the old springs should not be used as a specification for replacements. For example, the old springs might have been replaced with incorrect sizes because the last repairman didn't have the right one on his truck. If your door has never worked quite right, something like this might be the cause. To correct this, you must use the weight of the door to specify the spring, either from a spring rate manual giving spring torque constants, or from the formulas below.

With over 300 independently moving parts, your garage door is a deceptively complex piece of equipment. To help prevent malfunctions and break-downs, it is a good idea to occasionally perform a garage door tune-up to keep all of these parts in good working order. A regular tune-up service by a Sears professional can prevent unexpected door problems and prolong the life of your existing equipment.

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