Extension springs have four characteristics: length, inside diameter, wire size, and type of end. Even though springs have these properties, manufacturers generally do not make their extension springs based on the dimensions you may find on your door. Every manufacturer has its own design for making springs.
Therefore, every extension spring is most importantly characterized by its weight. Most residential springs are manufactured in 10 lb increments. Extension springs for heavier commercial and industrial overhead doors are generally made in increments of 20 lbs.
The pulley system in the extension spring design generates this ratio. When the garage door opens 2' off the ground, the cable that attaches to the bottom fixture will also raise by 2'. This cable wraps around the stationary pulley and then travels to the second pulley. The cable wraps around this pulley and then secures to the track with an S-hook and a cable clip.
The second pulley is attached to the extension spring with the help of a pulley fork. When 2' of cable travels over this pulley, 1' of cable is added to the distance from the S-hook to the pulley. To keep the cable taught, the extension spring will also contract by a distance of 1'. Therefore, the range of the extension spring's stretch is 1/2 of the door height.
It is important that you replace your old extension springs with new springs that will properly match your door weight. This will allow your garage door to stay on the floor when it is closed and stay open when you open the door. Broken pulleys and cables frequently accompany broken extension springs, so you may have a slightly bigger project on your hands that you anticipate.
There are three important measurements that you will need to make to order the proper springs for your garage door. These are the total door weight, the door height, and the spring length.
Shake the door and each of the rollers. If one spring is broken, the weight you read off the scale will be 1/2 the door weight. If both springs are broken, the scale will read the door weight. For more information, see the first five steps of our Extension Spring Replacement tutorial.
If you have multiple springs on each side of your door, slide the scale under the side of the door with fewer functioning springs. Multiply this weight by the number of total springs on the door, and divide this number by the number of broken springs. If you have the same number of broken springs on both sides of the door, weigh the door in the middle, multiply the weight by the number of total springs, and divide by the number of broken springs. These calculations will give you the total door weight.
The door height also helps to determine which springs you need. For example, the extension springs made for 14' high doors are intended to stretch twice as far as the springs made for 7' high doors. As a result, the un-stretched length of an extension spring generally increases as the door height increases.
Another measurement you will need to make is the un-stretched spring length, not including the ends. Extension springs tend to stretch over time so you will need to compress the coils when measuring the length. You may need to insert a shaft in the middle of the spring to keep it straight while compressing the coils. Some springs are ruptured so badly you may need to measure and count coils to calculate the length.
While the door industry has standardized on spring lengths, there are multiple spring lengths for some of the more common door heights.
If you decide to purchase an extension spring with a shorter un-stretched length than your old spring, you will need to adjust your cables. There will need to be 2" of additional length for every inch that your new spring is shorter than the old spring. If your cables are not adjustable or are too short, you will either need to replace the cables or order a longer spring. If you need a spring with dimensions not listed in our parts catalog, we can order a custom spring. These generally cost about 50% more than our standard springs, so it is probably better to change the cables instead.
If your new spring is longer than your old spring, you will need to adjust the cables to shorten the pull. Sometimes this requires mounting the S-hook on the new springs closer to the garage door.
Open looped ends are extremely easy to change. You will not need to open the eye-bolt, and you will not need to disassemble the pulley. One disadvantage, though, is that the whole spring relies on open wire at the end. If this is the only part of your spring that is broken, you may be able to save a few dollars and some time if you put a clip on the end of the spring.
Double looped ends are more sturdy than open loops, as there are two coils of the spring that connect to the eye-bolt and the pulley. One disadvantage, though, is that they take longer to replace.
Clipped ends are even more durable than double loops. The spring clips put less stress on the spring ends to help lengthen the life of the spring. The clipped ends come standard on extension springs of each door weight starting at around 200 lbs. The disadvantage, though, is that they can be more difficult to replace.
We recommend that you replace all of the extension springs on your door. As the springs fatigue, they get looser and do not provide as much lift. If you only replace one of two springs, the door may open unevenly and cause problems.
If you have multiple springs on each side of the door, you should still replace all of your springs. Only replacing one will cause your new spring to do more work than the rest of your springs. As a result, your new spring will not last as long before it breaks.
Extension spring cables wear out very often with the springs. If you examine your cables right now, you may not see any problems. Many times, though, the cable is frayed or worn in the cable clip, and the cables need to be replaced. This is something to consider when looking to purchase new extension springs.
We suggest that you replace both cables. Even though one may not be worn out, it will save you the trouble in the future. The prices for the cables for other door heights are determined by the length of cable needed.
Safety cables are very important to have on extension spring doors. You typically will not need to replace these cables, but if you do not have them, you should consider purchasing them. The cables run through the length of the spring and contain the pieces of the spring when it breaks. These protect people from injury or death, and they protect cars and other valuable items from being damaged when the spring breaks.
All of the extension springs in our parts catalog are listed with the door height and weight and the spring's stretch. The form in the following section will guide you directly to the extension springs your need for your garage door. The following steps can be performed to find your extension springs through our parts catalog.
Select the proper door height.
The spring stretch is written as a number like 25X42. The "25" refers to the un-stretched spring length. The "42" is another indicator that this is for a 7' high door. Unless you intend to purchase a spring with a different length than your current spring, the first number of the stretch should match your spring's un-stretched length.
The weight indicates your door weight, given that you have one spring on each side of the door.
Let's look at a few examples. Let's say you have an 8' high door that weighs 210 lbs, and your spring is 27" long. If you have one spring on each side of your door, you will want to purchase two 210-lb extension springs for an 8' high door with a stretch of 27X48". While each spring will be lifting 210 lbs, the pulley system makes each spring lift 1/2 the door weight.
Let's say that you have a 10' high door that weighs 500 lbs, and you have two springs on each side of your door. The combined system of two springs on each side must lift 500 lbs because of the pulley system. Therefore, you will need two 250-lb extension springs for each side of your door, totaling four 250-lb extension springs for a 10' high door.
Fill out the form below to find the extension springs in our parts catalog that match your door. If you need any additional hardware including pulleys, pulley forks, cables and S-hoooks, see our extension spring hardware page.
Be sure that you replace all of the springs on your garage door. Replacing only one spring often causes an imbalance as the old spring has typically lost some tension. If just the loop on the end of your spring broke, consider purchasing just an extension spring clip on our extension spring hardware page. Installing the clip on the last two coils or so of the spring may allow the homeowner to continue using an old spring longer before needing to replace the springs.
Because of the variation of manufacuturers and the loss of tension in extension springs over time, your new extension springs will likely look different then you old springs. This is normal, and assuming that your new springs are for the same door height and have the same pull as your old ones, they will be fully compatable.
If you want us to check your calculations, you can also send us your door weight, the number of springs that were holding the door, the total number of springs on the door, and any door information (manufacturer, model number, etc.) that you can find.