Question about Sears Craftsman LiftMaster Chamberlain Garage Door Opener Wireless Keypad Model 976LM Security+

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Model 139.536006 I have a 1988 model and had the same problem as pk5353 after replacing the sprocket assembly/worm drive. It would spin a few seconds and shut off while the limit assembly was no where near the contacts for the upper and lower limits. (I disconnected the chain to remove stress and left the back off so I could watch the limit assembly move back and forth.) My sprocket assembly kit cam with the collar with the two allen screws but I did not install it since my original model did not have it (like pk5353). I replaced the black cap and it appears secure but the motor keeps shutting on and off. Should I try putting the collar on? Any other speculation?

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SOURCE: 25 yr+ old Sears opener runs past lower limit

Update: I remembered that I had a problem with the door reversing too much a while back. It was chattering in the tracks and I could not fix it with lubrication and changing spring tension. So I dialed up the down reversing force. This contributed to the jam-up I had when the lower limit was ignored. If I had a lighter force, it may have at least reversed.

After futzing with it I left it alone for several hours. The motor would hum every few minutes. I was considering cutting power to it overnight. I pressed the remote one more time and the motor ran normally to a limit and stopped. I tested it a few times then reconnected the chain and door. Seems fine now. I suspect an intermitten logic board problem. I'll try lightening up the down force and using it for a while.

Posted on Jan 07, 2009

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