I just had the same exact problem as kurtzj. I installed a new gear on the drive shaft and after that, the motor would only run a few seconds in either direction. I found an old post from sage66 that described the problem and actually contained a few photos that really helped. There is a small green led on the motor housing control panel that was blinking 5 times constantly. Apparently, this is an error code that says the door sensors are not aligned, or the rpm sensor is bad. The rpm sensor is a small circuit board with 4 wires next to the limit switches. There is a round black cap on the end of the drive shaft that has slots on the side, called the interruptor cap. This spins with the motor and the slots pass through the rpm sensor, which has an infrared sensor that it passes between. If the drive shaft has play that allows it to slide forward, the motor will shut down after a few seconds when the interruptor cap jumps out from between the sensors. What you need to do is take off the interruptor cap, and loosen the 2 allen screws that secure the thick brass ring and lock it to the shaft. Move it away from the motor enough to get a screwdriver blade between it and the washer behind it. Lock it down there and use a screwdriver to pull the shaft forward away from the motor all the way out. Loosen the 2 screws again and slide the locking ring all the way back to the washer without moving the shaft. Tighten the 2 screws and put the interruptor cap back on. This prevents it from jumping out from between the rpm sensor. After i did this, it worked fine. I hope this helps someone else, because I never would have figured that out without help from sage66. The internet is great! Good luck!

I have a Craftsman GDO that suddently developed the following problem. When closing the door with a remote the door will only travel a few inches and then stop (as if it struck an object) and reverse direction. I have to repeatedly press and repress the remote to coax the door all the way closed. When I shut the door with the wired button it will close all the way only if I keep the button depressed until closed. I have NO problem opening the door. I have adjusted the tracking force and distance switches and unplugged and replugged the unit to no avail. Thanks for your help. Ron Licata Weathersfield, CT

I have changed this part many times. If you are able to make the change, then is likely worth it,(if you are going to pay Sears to do it, then don't do it. You will pay more than it is worth) You can get them reasonable on ebay. It is the top metal gear, and has a large white gear connected on the bottom. I don't recall the part number, as I recycle them from removed units,(I beleive the part number is listed in the post above) It is mechanical surgery, if your okay about that. Remove the door opener power head from the ceiling and put it on a table to do this one. You may want to take a picture of the internals before you start removing things to get at the part to change. Dan

Things have changed for the better in the last 20 years and I would opt for a new opener.