Place scale under the garage door on the side of the door with the broken extension spring.
How to change a garage door extension spring.
At the far end of the door rail remove the spring end from its mounting pin.
The following steps will walk you through how to replace an extension garage door spring.
This video will show you how to replace the extension springs on your garage door.
Do not use a digital scale as they often will not respond to the door weight changing as rollers no longer stick to the track.
Open the garage door to remove all spring tension and clamp it in place.
The new spring s diameter length and wire size or gauge must be the same as your old spring.
Purchase new garage door extension springs.
The easiest way to do this is to take the broken spring to a local garage door dealer or home improvement center so they can help you find an exact match.
If both springs are old you should replace them both at the same time.
Disengage the broken extension spring one end at a time.