Thursday, January 24, 2013

Repairing a garage door

When I came home last night, and tried to open the garage door, it got halfway up and jammed, at a small angle.  Experience suggested this was a broken spring.  It was.

There are two coil springs on each side of each of the two garage doors.  Gravity pulls the garage door down, and expands the springs as it does.  The springs then help pull the door back up when it is opened. 


These original springs were installed when the house was built (1986).  They tend to break at the ends, and looking at the breaks, the steel they are made from is cast steel.  Repairing them is just replacing the springs.


One problem is what size of spring to get.  I went to Home Depot and found the garage door opener section.  They had springs from 70 pounds to 160 pounds.  This should be a measure of how much the door weighs.  You want a spring which roughly pulls back with a little less than the force of gravity pulling the door down, so that a little work will bring it up (spring plus work exceeds the pull of gravity) and a little work will bring it down (gravity plus work exceeds the pull of the spring).  If the pull of the spring is exactly equal to the pull of gravity, the amount of work needed to open or close the door is minimal.

Not knowing the weight of the door, I picked 140 pound springs.  I think at one point I tried to weigh the door, but that's not easy.

The box from Home Depot comes with two springs, plus safety cables.  The safety cable runs down thru the length of the spring, so that if it breaks, most of it is held, more or less, in place.  The spring almost always breaks when it is extended, and will then shot back towards the anchored end with a lot of force.  Plus the broken piece can go shooting off too.

It took half a day to replace the two springs, plus two trips to Home Depot.  In addition to the springs (first trip), I needed two Steel S-Hooks (2 inch size) to attach the end of the spring to the garage door support -- a piece of slotted angle iron, one for each door.

The box comes with two springs, so I replaced both of the old springs on this door at the same time, and installed the new safety cables.  Then I lubricated all the moving parts and tightened all the bolts.

The springs on the other garage door were replaced earlier.  Now we have new springs on both doors.