If both springs are the same length the garage door should be level across the floor.
How to install double garage door extension springs.
Many manufacturers have cut costs by using a single spring on a double wide 16 steel garage door.
Tie the extension spring to the roller track then detach the cable from the bottom bracket with a pair of pliers.
If the extension springs are not the same length open the garage door and change the location of one of the s hooks so that when you close the door both springs are the same length.
Extension springs the other kind of garage door springs are torsion springs run alongside the upper garage door tracks the ones that run parallel to the ceiling and stretch or extend out and back to help lift the garage door.
Garage door springs offset the weight of the door and allow it to open and close with ease.
Be sure the door is open and supported when doing this.
Other problems frequently ensue when a single spring is used on a double car garage door.
Release the tension on side mounted extension springs by lifting the door and locking it in place on each side with a pair of locking pliers.