This guy will answer your questions. You must get the right springs. There is usually a splotch of color on one end that identifies each spring tension. I don't remember if he refers to this or not.

http://www.truetex.com/garage.htm

Hi there. I just had to chime in as my garage tension spring just broke two weeks ago. If you have basic fix-it skills and are capable of simple assembly, this project will be a breeze. BTW, Home depot does sell these springs, they're usually around $10, and you can also find on their website. First, look at the end of your broken spring, there'll be a spray of paint, probably green or yellow. Then, go to the store and get the spring with the corresponding color. AFter that, se-up your step ladder and re-attach the new spring, using the still-good spring on the other side of the garage door as a reference. The total repair time was 15 minutes.

brendog you are talking about a completely different spring and FYI you should always replace both springs, even the type you are referring to. A torsion spring does not stretch, it twists.

Yea, I think so too that brendog is talking about those regular tension spring for fixed garage door not the "torsion" spring that is typically used for sectional garage door. Two facts. $10 is way too cheap for the torsion spring, and 15-min is way too fast to correctly set up the torsion spring as far as I've researched. I finally adjusted mine (has only one torsion spring for 2-car door). The torque of the spring when fully wound up is deadly high - so be VERY careful if you are going to do it by yourself. I heard the total duty cycle is about 7 years long, assuming you open/close twice a day. No retail stores that I know sell those spring to public. But I found some web-stores would sell to you at about $25 to $40 a piece, depending on the size (length and the coil "wire" diameter). I called some pros found in yellow pages and those are all way over-priced, wanting me to charge $150 at minimum just for labor. It took me about an hour to set up the totally relaxed torsion spring.

Replacing or adjusting TORSION spring seems very intimidating when doing for the first time. But with proper knowledge and tools, it can be done safely and relatively quickly. You need a special tool but you don't need to buy from stores. The special tool you need is a pair of 36" or 48" 1/2" dia. round bars to hold/rotate the clamp at the end of the torsion spring. And you would need a pair of locking vise grip to hold the tube while tightening the set screws on the clamp after winding up the spring (the number of roation/winding of the spring is critical - 8 turns on mine).
All the installation/adjustment is done with the door closed. Don't try to lift up the door with relaxed spring(s) by yourself for any reason. It is dangerously HEAVY.

Don't be taken by scammers who put ads on yellow pages and Penny Savers saying they are the garage door speicialists.

luvr29 if you have a door that weighs 400lbs that has extension springs, you need to have a professional come out and change out those springs. You don't need new cables if they are not freyed and the last thing you want to do if you are unsure of your anchor points, as you refer to them, is close you your door and check them with the spring fully loaded like that.

I have no idea what you are talking about with this tool that looks like a bolt cutter to remove torsion springs. Individual bars are used they are called winding bars, the clamp you and referring to is called a winding cone and the only reason the vice grips are on the torsion bar is to hold the cables in place until you get tension on the springs.

There are various types of torsion spring systems out there. Some doors only have one spring, others two and they are not always mounted in the center. Some are mounted on the left and right side. You don't always wind up on the spring, sometimes you wind down. Amount of turns depends on drum diameter. For the doors today most of them require as many turns as the door height plus a quarter to a half of a turn, others require only 5-6 turns (1" 19/32nd in particular).

Springs are to be taken very seriously no matter what kind they are. They are all dangerous even if you know what your doing. If you want to learn how to do them, I would recommend watching a professional a couple times and have him or her supervise while you attempt to change them.

here is a short and clear explanation:

http://mhandbook.com/garage-door-torsion-springs/

Here is a link that might be useful: garage door spring cost and replacement