When you can’t get in or out of your garage because of a broken spring or other technical difficulty, it’s best to know a little about options before opening your wallet.

“THAWONNNNNNNNNNNNNNG!!!!�

It sounded like one of the neighborhood skateboarders slamming headfirst into a steel trash can.

But it wasn’t. The reverberating noise turned out to be one of the tightly wound tension springs on our overhead garage door rapidly unwinding after snapping in half.

My husband and I put two and two together later, when the garage door refused to open.

Next morning, we were much wiser in the ways of overhead sectional garage doors. We also were almost $550 poorer after paying a company with a really big ad in the yellow pages to come out and fix it.

The most important thing we learned is that when garage-door disaster strikes, you really should shop around. We might have gotten bids as low as $300 for the same work had we not been in such a rush to repair.

There are pricey differences in material--though springs have limited lives so it often doesn’t pay to buy the most expensive ones out there. And, we learned, there is nothing you can do to avoid a broken spring if you are one of the tens of thousands of homeowners with overhead sectional doors that slide up a set of steel tracks and tuck in under the garage ceiling.

And when they go, you can’t visit the local home-improvement warehouse and buy new springs.

We’ve owned two other homes, but they had the old-fashioned swing-up doors with springs that can be bought and installed by a reasonably handy homeowner.

They don’t sell them for overhead doors, though. It’s a matter of safety, according to people who make a living fixing springs.

“Those springs are wound with a couple hundred pounds of tension, and if you don’t have the right tools and the proper training you can do a lot of damage to yourself,� said Greg Brittain, president of All American Door Inc., a Fullerton sales and repair company.

Brittain said he was taken aback by the price we paid to have our door repaired but didn’t disagree with anything our repair guy said.

And after learning that we’d paid for galvanized springs with a 15-year warranty, he allowed that we probably weren’t overcharged, though we might well have bought way more than we needed.

When we examined our garage door to find out why it wasn’t opening, we quickly spotted the culprit--both springs were snapped in half and hanging loosely coiled around the torsion bar mounted above the door opening and traversing its width.

(A standard double garage door, 16 feet wide by 7 feet tall, takes two springs, one on each side of the center-line of the door. A single door takes a single spring.)

The springs are made of different qualities and diameters of steel, which determines how much weight they can lift and how many cycles (one opening and closing is a cycle) they will run through before snapping like a piece of uncooked spaghetti.

They also come in regular and galvanized steel--the galvanized product being less likely to rust. Brittain said that galvanized is worth the extra cost if you live on the ocean, where salt corrodes everything metal, but probably won’t make much difference in a spring’s life span out of the immediate coastal belt, as we are.

The typical tract home uses pretty inexpensive springs--every job goes to the low bidder in the mass-production housing market. They typically last about 10,000 cycles, Brittain said. That’s up and down an average of five times a day for six years.

Even an experienced technician can only guess at the condition of a set of springs unless they are brand new or one is broken. “No way can you just look at a spring and tell that it’s worn out,� Brittain said.

But there are other warning signs. Cracked or loose hinges, loose tracks or a door that sags when in the open position are all telling you that some maintenance is needed, Hanson said.

The repair company we called said springs cost $70 to $140 each and they wouldn’t be able to tell which we needed over the phone. As it turned out, we needed the expensive ones. We also needed new bearing plates at $69.95 a set. And because the metal lip on the inside of one of the door panels had started tearing, we needed a 16-foot galvanized steel strut that runs across the width of the door and stiffens it to eliminate sagging and flexing that would worsen the tear.

That strut is where we probably really overpaid--the bill was $108, installed, and the installation took all of five minutes. Brittain said he sells struts for under $30.

There was also a flat $55 service fee. That included an overall inspection and lubrication of all moving parts.

Though both of our springs were broken, it is highly unlikely they snapped at the same time. That almost never happens, Hanson said. A single spring can continue raising the door for a while but will eventually break when the stress of raising the door unassisted finally gets to it.

So if one spring has gone, expect the other to go shortly. And never replace only one spring--the difference in tension will throw the door out of balance and could damage the opener.

Finally, make sure that the opener is properly adjusted to automatically reverse if it hits an obstruction (like a child or a pet) on its downward travel. The usual test is to place a 2-inch-thick piece of lumber on the floor and close the door on it. If the door stops and backs up as soon as it touches the wood, all is good., If not, the reversing adjustment needs to be fine-tuned.

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Times staff writer John O’Dell contributed to this report.

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How to Keep It Rolling

Here are a few preventive steps to keep an overhead garage door working well.