Garage door

My garage door opener keeps going out of sync going down. Sometimes the door stops short of closed and other times it goes down but then goes right back up again?

Have adjusted numerous times, even shorting the arm connected to the door by one hole (inch) as the door mostly bumps and goes back up. Sometimes the door stops short; about one inch up off the floor. What do I do next? This is a Craftsman garage door opener model #139.53910 that worked great for three years.

It sounds like the Travel Limit Switch is not functioning properly.

Looking at the parts illustrations in your Owner's Manual or at the Sears PartsDirect site, such as shown in the images below, might help you determine what is happening. The Limit Switch Assembly is item 14 in the images and also is shown in more detail in the box on the lower left of the first image and in the second image.

The contacts in the Limit Switch are small strips of metal and they can bend over time, or get snagged or caught, and even a small change in their position can dramatically effect where the door stops. In fact, two of the contacts connect to the same screws used to adjust door travel limits and the other contacts moves with the door, so any change to where the contacts meet each other is supposed to change where the door stops.

Problems with the switch contacts typically cause one of two things to happen. The contacts touch too soon and the door Logic/Control Board thinks the door is already closed so it stops the door too early. Or, the contacts never touch at all and the board keeps trying to lower the door until the safety systems sense too much force being used (since the door is pressing into the floor) and reverse the door back open. Sometimes a poor connection with the wires going to the Limit Switch can do a similar thing.

Another possibility could be excess wear in the Worn Gear Assembly, item 3 in the images. Wear there can allow the drive gear on the Limit Switch to slip or skip a gear on the worm gear. That gear keeps the center Limit Switch contacts moving in-time with the door so, again, that would change the position the door stops at. If the Limit Switch Assembly is not securely in place it could also cause that gear to skip.

If it is still not clear what is causing the issue at that point feel free to submit another question here with any updates and we will do our best to help further.

Or, you might want to consider having a professional inspect the opener since it might be related to the control board or one of the other major components and may be difficult to diagnose or repair. You can call 1-800-4MY-HOME (800-469-4663) to see what options there are in your area for professional inspection and repair.