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Update

I was able to screw the roller fixture back into place, however, the right side now rides high:

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Many thanks to Trevor's helpful response. Given isherwood's feedback I will attempt a more specific follow-up question: Should the right-side gap be corrected \ closed by tightening the tension on the left or reducing tension on the right? Any explanation of why is appreciated.

ORIGINAL POST

In an attempt to replace the (bottom) roller of the garage door, I did not notice that it was tied to a cable and now it is difficult (if not seemingly impossible) to restore because of the cable length seems short. The reason for replacing the roller is that was exposed to saltwater flooding and it may be the causing the door to stop after moving 2 inches (from either the open or closed position).

Is there a good explanation and video that can explain the purpose and mechanism so that I can safely restore the garage door back to working order? If I can learn how the mechanism works from a good-simple youTube video or URL, then I can troubleshoot the other umpteen garage doors in the community. Thank you for an lessons-learned and pitfalls to avoid.

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There should be a cable on both sides of the door that go up to pulleys on a long rod mounted above the door. In the centre of the rod will be a large coil spring that is affixed at one end to the wall.

As the door is brought down the rod rotates and winds up that spring. The spring acts as a counterweight for the door so it only takes a few pounds to lift the door rather than lifting the entire door weight.

When the door is fully open the spring should be relaxed. When open, each pulley can be untightened separately and turned by hand, or with a lever to adjust the tension on the wires.

DO NOT ATTEMPT that with the door down. There is a lot of energy stored in that spring.

Getting the tension the same on both sides is important to ensure the door travels true and mates with the floor evenly.

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The springs can kill you

Garage door springs are quite dangerous and can kill you (them, or the force of gravity which they counterbalance).

Raising the door to the top eases the spring tension, but does not eliminate it. That preload is important for balance. It's also hard to adjust the sides equally with the door at the top. What I do instead is lower the door to the bottom, then correctly use winding rods/bars to windup the spring a little further, barely slacking the cables, then use another bar to pin it there. Research how to use them properly online. There is nothing magic about winding bars, they are just steel rod, but use the correct size for the receptacles on your spring casting!

Don't slack the cables too much or they will fall off the pulleys and you'll have a real mess.

Tram (one side higher than the other)

There is a pulley-spool on each side of the door. The cables winding onto those pulley-spools lift the door from each side at once. They must be in sync or your door will tram. They are kept in sync by a shaft which runs between them. They are not kept in sync by spring tension, and changing spring tension will not correct a tram problem. In fact, the spring(s) act on the one shaft, so changing spring tension will affect both pulleys equally.

Usually, tram means that one pulley or the other has slipped on the shaft. It can also be caused by a stretched cable (replace both cables; the cable is dangerous and cables need to be matched).

In your case, however, the tram issue is because you reassembled it incorrectly. I would wind the tension off the spring(s) so the cables go slack, then go through everything with a fine-tooth comb until you find it. You should not mess with any of the set-screws on any of the springs or pulleys.

Cables don't randomly shorten. They do however get snagged or attached wrong. If the cable is damaged, replace both cables with ones of the correct length. You can buy cables of pre-made length, or you can make your own cables; but in that case you must be very careful to get the crimps correct; if the cables fail, the door will drop. If you didn't do one crimp very well, and the full weight of the door falls onto the other crimp, most likely it'll fail.

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