The important, and also the most damaging part of the overhead door will be the garage door spring - (or springs based on the design), which supports the whole weight of the door panels (sometimes over 400 lbs) and helps you to lift / lower the whole door meeting.
I have personally installed 3 overhead garage doors using 2 different types of springs, and you do have to trust me on this - garage door springs are under huge pressure and also you can get seriously injured or murdered when doing this type of work. If you decide to take your opportunities -
Even when you have a buddy or a professional performing this to you, read it and check all after the installer finishes the job. The garage overhead doors have no safety wheels (at least that I haven't heard about any), that would keep it from falling down if the supporting spring neglects. I have discovered some US patents for such devices, but apparently not one of these were ever implemented into a real garage door.
You may also have an older, one piece door that swings outward as it goes up and overhead. This particular design will have springs mounted on either faces of the doorway opening - in about your waist height, secured to a lever mount system that extends the springs to the ceiling at the door closing. It's a classic and incredibly perilous process, not fabricated. When you have such a method in the garage, then I would highly recommend replacing it.
Garage door torsion springs - out you will find either single or double spring layouts. The spring will usually break while beneath the maximum stress that's as soon as the overhead garage door closes / journeys down, also it is already fully shut. If you are shutting it manually and it happens during this surgery, don't attempt to block it from beating down, let it move ... well, unless your foot is the point where the door will hit!
Garage door extension springs - you may have either one or two on every side of your overhead garage door A critical issue with these springs is to have a safety cable installed inside of each single spring and fastened properly, so when the door opens and closes, the spring can freely slide onto this cable! When the garage door spring snaps with no cable indoors, broken endings may severely hurt anyone standing in their range.
The cables should be always included with all the overhead garage door components (supposing that they came armed with extension springs), but A LOT of people either forget to put in them, or do not read instructions and maybe assume that they are not required.
Unlike the torsion spring, which does not really demonstrate any visual wear until it breaks, extension spring wear is far less difficult to place, since they simply change measurements: the coils are over-stretched (best visible when the garage door is available). If you see such a behaviour on your own garage door springs - it is time to get a replacement.
And for both types of the garage door springs - the pressure should be evenly adjusted (on a two spring method) so the overhead door travels properly in its paths - to examine it, halt the door slightly over the garage floor (1" or 2) and ensure that its bottom / top border are perfectly flat. Measuring the gap across the bottom might not be the very best approach to confirm that, since the garage floors are often out of level.
Putting a flat somewhere in the center section of the garage door high edge would give you the very best readout (recall that the door shouldn't be closed entirely!) . Once the springs are correctly adjusted, you need to be able to lift and block the garage door in any given height, and it ought to stay at the level with no help ( garage door opener arm disconnected).