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

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Installed new worm gear, but now i cant get the door down

I installed a new worm gear, and now the chain moves. According to the instructions I need to get the trolley to the closed position before I hook the door up. Even after adjusting the distance and force I cannot get the trolley to move to the closed position, it only moves about a foot down the rail, no matter how I adjust the distance or force. Thanks for your help.

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  • quincyw Jan 09, 2009

    I think I hook it up but wil double check. Thanks.

  • quincyw Jan 09, 2009

    I checked the wire harness and it is connected.

  • Anonymous Jan 12, 2009

    I checked the shaft and its seems to stay perfectly straight when rotatating. What if I take the chain off the sprocket and manully slide the trolley down. Also when I press the opener the trolley starts down (closing) shouldnt it start sliding to open?



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Check to see if the 4 wire harness is hooked up from the limit assy.

Posted on Jan 09, 2009

  • Joseph Chapman
    Joseph Chapman Jan 10, 2009

    Check the movement of the motor shaft. (not the turning of the shaft) The movement back and forth should not be move than 1/32 of an inch



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I have a craftsman garage door opener 1999. it goes two feet and then back down. I can open door with one hand. all gears are new as i rebuilt it (Twice).

Your "timing" is off. Disconnect the door from the trolley and tie down the door latch assembly so it does not engage the trolley. Then using the up down button on opener open or stop the trolley at the closest position you can to the motor assembly. Then open the door to the position it would be when open and note where the latch is at that point. Then loosen the drive and move the trolley to the position noted in former step.- then tighten the chain.
Now hook up the door latch to the relocated trolley and play with the up/down adjustments till you get it right.

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Check the track rollers. Lube if dry.
Check the trolley, lube as needed.
Check the long lead screw the trolley follows, lube as needed with lube for that type of opener. If it is in the motor housing, is it time for a new opener?

I had an opener that drifted in adjustment, that would go beyond the closed position a little causing the rail to bow upwards a little once closed, putting strain on the gearing shaft bearings and wore them out. I was able to order a package with the pinion gear, drive gear and sprocket and bushings, including the pulley for the opposing end in one kit.

-Disengage the trolley from the belt, chain or lead screw.
-Unplug the power before opening any opener covers and servicing anything inside the unit.
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Adjust your open and close positions on your door opener. Only adjust one at a time. Once you make an adjustment try to open and close. If it gets worse, go the other direction. If it does not change anything, then go to the other adjustment and repeat the process.

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Is the trolley jammed against the bolt just in front of the motor? If so, loosen the chain until the tension is off the trolley and then run the motor until the door is closed. Now locate the up limit on the side of the motor unit and turn this control 2 full turns in the opposite direction of the arrow printed on the cover. Tighten the chain.

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1 Answer

My 20 yr. old Craftsman 1/2HP chain drive GDO (139.18590) will click and hum for a second but the door doesn't move when I press a remote or wall console. The door moves freely manually and I checked the...

If your door is stuck in the open position the trolley is most likely jammed against the bolt just in front of the motor unit. You should be able to loosen the chain enough that it releases the pressure on the trolley and then close the door. While the door is closed, locate the 'up limit' control which is on the side of the motor unit. Turn this control 2 full turns in the opposite direction of the arrow printed on the cover and then tighten the chain.

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1 Answer

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Some of your comments look like they're missing but from what I can see you had to put chain back on and now the door doesn't close all the way.take the cover off and look at the limit switch,this the travel adjustment. The switch for the close side is making contact too soon so it shuts off early.You need to adjust contacts so its further away. Depending on where the trolley was when you reattached the chain, you might not be able to adjust it back enough.But try it first. If you still come up short you will have to take the chain back off and move the trolley back to where the door would be closed and reattach chain. now open position will probably need adjustment leave door unhooked and just let trolley move in case it over shoots the mark either way.

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1 Answer

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Unplug the unit and remove the cover, usually eight screws, if you see a lot of white dust in the cover check the nylon drive/worm gear, they will need to be replaced.

Apr 10, 2009 | Sears Craftsman LiftMaster Chamberlain...

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From your description it sounds like you forgot to plug in the RPM sensor.

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1 Answer

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check the end shaft platic cap is installed and runs freely between the rpm sensors.. that might be ur problem..

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