Replacing a "torsion spring" is dangerous.
In my opinion it's not a do-it-yourself job.
There are two kinds of garage door springs -- torsion springs and extension springs. Torsion springs are the kind wound-up on a rod above the garage door opening. There are a pair of them--one on each side of the center of the door. When one breaks the other often follows, so save the cost of another service call, and have both replaced when one breaks. People have been maimed and some killed tightening or releasing these springs. Hire a professional.
If you are hell bent on replacing one yourself rent a spring tensioning tool--probably have to find one at a garage door company. They look something like long handled bolt cutters but, the business end it a ratchet to hold the bar as you tension the spring. USING INDIVIDUAL CRANKING BARS IS DANGEROUS. Skydiving is safer.
Here is a chap who uses ridicule and sarcasm to say you're a woussie if you're afraid to do this job yourself, equating the danger to cleaning your gutters or fixing your car. Keep in mind the many reports of people being maimed doing this as you read his quite thorough instructions, then decide if you want to spend 4-6 hours to earn about $70 this way.
The other kind of springs -- the kind that run along the upper, right and left door tracks, and extend/stretch to do their job, called extension springs -- are not as difficult or risky a home repair. However, some safety measures are in order. Remember, when these springs are extended (door down) they are stretched to potentially deadly force--they may be lifting a 400 pound door.
Here's the best how-to description I've been able to find on the net.
From: Doorman (firstname.lastname@example.org)
1.0 With the help of a friend, lift the door (it will be very heavy) to the fully open position, and place a pair of locking pliers (ViseGrips) on the door track directly under the bottom most roller which runs in the track. (Broken spring side of door).
2.0 Remove what's left of the broken spring. Check the sheaves [pulleys] and replace them if there is significant wear in the bearings, and or if the sides of the sheaves are worn were the cables rub.
3.0 Take the broken spring to your local overhead door dealer and purchase two new springs, identical in length, diameter, and [gauge/wire size] as the broken sample. It's a good idea to pick up new lift cables as well, particularly if you notice any sign of kink or fraying. Remember to check those sheaves and replace if worn.
4.0 Don't disturb the unbroken spring yet as you will need to see how the cable is woven through the sheaves as you replace the broken side. Install the new spring, cable etc. ensuring that the spring is stretched no more than about 1" (door fully open). You may have to adjust this later.
5.0 Move the locking pliers over to the other side of the door and replace the old unbroken spring, cable, etc. in the same manner.
6.0 ENSURE THAT NOBODY IS STANDING NEAR THE SPRINGS. Remove the locking pliers and carefully lower the door with an eye on all that you have replaced. As the door nears the fully closed position, the sheaves located in the end of the spring, must not touch the other fixed sheave, and they might if you stretched the spring out too far when you installed it. Observe the anchor points of the spring to ensure there is no danger of them pulling free from their moorings.
7.0 If the door is heavy to lift and providing there is adequate space between the fixed sheave and the spring sheave, open the door, reposition the locking pliers, and stretch the spring out another 1" or 2". DO NOT EXCEED THE AVAILABLE DISTANCE BETWEEN THE TWO SHEAVES THAT YOU OBSERVED WHEN THE DOOR WAS FULLY CLOSED.
8.0 Finally, make sure that there is safety cable installed, which runs through the springs, and anchored past the further most travel points of the springs. This is important to help retain the springs if they should ever break. I have seen these types of springs when unrestrained go right out through the roof, or wall on occasion, and I have also heard of cases of serious injury to people standing near a spring that has suddenly broken.
my way of saying step 8 above. Add a safety cable if there isn't one already. A
safety cable is a roughly 3/16" braided steel cable
threaded through the center of the spring (Thinking of the spring as a tube, the cable is threaded
through the tube.) and anchored securely at each end (often to some part of the track support)
and, positioned so it cannot interfere with opening and closing the door. This cable shouldn't be
taut. If the spring breaks this cable will hold the parts, keeping them from shooting into
something or somebody.
Here's some discussion:
Steve Perry writes:
> Subject: Garage
Door Torsion Springs