Lifting a with a broken garage door spring is dangerous. However if you need to be prepared to lift at least 100 lbs. The garage door is heaviest at the bottom, and as it continues up onto the horizontal tracks it lightens up. Be sure to have someone with you incase of an accident. If you have a garage door opener, get the person with you to press the button simultaneously as you’re lifting, this way it will help lift 20-40lbs with you. When you get the door to the top position make sure you have it locked in place; prop it with a piece of wood, a ladder, vice grip, or if you have a garage door opener it will keep it in place for you
Typically you can find 2 torsion springs on double car garage doors. In some cases, garage door openers can lift a door with a broken spring, but you are putting unnecessary strain on your garage door motor and the door itself. If you need to use it, help the motor lift the garage door simultaneously.