Why does my garage door opener only move a foot?
I replaced the drive gear on my garage door opener. The motor runs but the trolley only moves a foot. This is a Craftsman garage door opener model number 139.53976SRT. I have used this unit for years. Recently I had a company replace both of the garage door springs. The opener worked fine for a month, and then the unit failed I opened the motor cover, and the drive gear is flayed with plastic shavings on the bottom of the cover. I have replaced the drive gear/sprocket. I observed the drive and the worm gear operating as expected, but the trolley is at a position with the door about 2 feet off the ground. The trolley runs the door back and forth about 1 foot. I have checked the safety sensors, they appear fine, I tried adjusting the down and up limits and the force. Nothing has changed the amount of the trolley travel. The door seems to be free of any snags. The door operates smoothly with the manual released. I have also tried adjusting the tension on the chain which did not make a difference
Jimmy k
Expert
Remove the chain and cable assembly so that you may freely move the trolley. Place the trolley in the position that it was before you installed the drive gear/sprocket, once the trolley is in the former position, replace the chain and cable assembly. This should allow you to be able to open and close the door normally.
""Finally, when you the trolley and the chain operating properly, don’t forget to return your tension adjustment to the normal setting."" There is a lot of force behind even a small garage opener motor and it can be a serious safety concern if the setting are incorrect.Agarr
Newbie
Check to see that you correctly replaced the plastic cup on the end of the motor shaft. You had to remove it to replace the gear on the motor shaft. It runs the rpm sensor and the unit will not work without it.
Jkals
Newbie
Thank you agarr: That was exactly the right answer. That part got covered up by rags on my workbench when I was cleaning up all the old grease and gear dust/fragments. When I read your post I immediately remembered that I had forgotten to reinstall that cap.
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