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My Sears Garage Door Opener Model 139.53960srt is having a problem where the chain comes off of the sprocket when reversing during an emergency opening.

The chain on my garage door opener comes off of the sprocket when the door suddenly reverses during an emergency opening (e.g., when there is an obstruction). This has happened several times lately. Inspection of the sprocket shows that it is tilted slightly out of horizontal, and it appears that this is contributing to the chain coming off when it turns. Is this the cause and how can I fix. When I re-installed the last time, I made sure that tension was correct, so I do not suspect this to be the problem. Please help. Many thanks.

Garage Door Openers , Garage Organization & Shelving
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3 Answers from these members:
Korinna Sierra
I see Don informed you that the Gear and Sprocket assembly will need to be replaced to correct the issue you are having. I provided you with some information below to help you with this repair. If you do not fell comfortable repairing this issue yourself, service can be scheduled at the following link:

Sears Home Services

Unplug the garage door opener from the power. Loosen the chain at the trolley and remove it from the sprocket on the opener.

Remove the outer cover from the motor unit of the opener.

Remove the 3 screws that hold the sprocket and gear assembly to the top of the motor unit and lift the assembly out the top.

Remove the clip and the gear that drives the limit switch. Note the position of the door and of the limit switch. be sure they are in the same approximate positions when you reassemble.

Remove the screws that hold the motor to the motor unit housing and remove the motor unit. Mark the wires as you remove them so you can put them back as they were.

Drive the roll pin out of the motor shaft and slide the worm gear off the shaft.

I hope this helps.
by Korinna Sierra
October 20th, 2011
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