We do not have a garage door opener, but always open it by hand. Last week one side fell out of the track and I had to slacken the spring to fix it. The door is centred and is not rubbing against one side... so I'm assuming it is just the spring. Now that I put the spring back the door is very heavy, how do I adjust the spring to make it easier to open or close.

There are 2 different styles. With either one, you need to be careful and not let anything get away, or you could get hurt. Use your head, think twice before loosening anything, and you will be OK.

I am most familiar with the ones that have torsion springs directly over the door that you can't see unless the door is closed. To adjust one of them, close the door. There are wheels at the end of the springs that have 4 holes in them. You need 2 rods that fit the holes. If you don't have anything else, go to a hardware store and buy a 36'' steel rod the right diameter and cut it in 2. They should only be a buck or 2. Maybe round the edges a little to make it easier to insert in the holes. Insert a rod into a hole that will not let the shaft turn very far before hitting the ceiling or wall. Then loosen the pulley at the end next to the track. It has locking screws. Then use the first rod to tighten the spring a quarter turn. Insert the second rod, remove the first, and give it another quarter turn. Repeat until the spring is tight enough. If you need a break, you can always let the rod press against the ceiling or wall. I can't say how tight is tight enough. For the door to work right, both springs must be about equal. Otherwise, the door will be pulled crooked. I had to work on my door several times, but it has worked fine now for a number of years. I may have forgotten a important detail. Study the door carefully before you start, and do not hesitate to ask me to clarify any thing I said.

Some of them have tension springs, cables, and pulleys running the length of the overhead track. I have never worked on one of those. Maybe raise the door and prop it up. If you can pull the spring back and readjust the cable, maybe that will work. If you can't pull it back enough, perhaps a come along would help. Maybe you need help from somebody that has worked on that style.

Spend the 120 bucks and save yourself! Dangerous work.