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

2 Answers

Stuck garage door - Sears Craftsman 1/2 HP GDO, Model 139.18876

I just installed a new gear & sprocket assembly (Part# 41C4220A) along with the worm gear and all associated parts (bearings, etc.) since the old drive gear was totally chewed up. I didn’t know until afterward that they sell just the part that I needed; instead I bought the whole assembly and assumed I had to change it all. The problem I'm having is that when I run the opener, the sprocket will make a clockwise cycle but will immediately do a counter-clockwise cycle in the same distance. I've done it without the chain and with the chain attached and it's the exact same thing either way. That is what happened initially before I changed the gear & sprocket assembly; the door just opened 3/4 of the way and then wouldn't move at all (because of the chewed up drive gear). Now with the chain attached to the sprocket, the door moves a few inches up and then back down to where it started from, making the overall movement zero. The sensors are aligned and nothing is obstructing them because the lights don't blink when this happens and when I deliberately step into the sensor, the lights do blink. I tried adjusting the force and amount of travel but nothing happens. Nothing else is broken or stripped anywhere throughout. All wires were fine & plugged back into their proper spots. After the repair, the door is moving whereas it wasn’t before; it's stuck in the same position that it broke in. Since it happens with or without the door, it can’t be anything to do with the door or rails. I even tried running it without the light switch assembly and RPM sensor plugged in and it’s the same thing. Any help/suggestions would be greatly appreciated. Thanks.

Posted by on

  • andylanders1 Feb 14, 2009

    I have the very same problem.

    Did you try this? Did it work?



2 Answers

  • Level 1:

    An expert who has achieved level 1.

  • Contributor
  • 1 Answer

I HAD the same problem. I just solved it.

Here's what's wrong...

There is a black plastic "notched" wheel that attaches to the very end of the motor shaft and operates the RPM sensor. I found that when I reassembled my unit I did not get this wheel far enough onto the shaft and therefore it wasn't fitting far enough into the RPM sensor.

I had to take the motor back off, loosen the Allen screws on the shaft collar and push the collar further onto the shaft. There should be very little back and forth "play" in the shaft. This makes the RPM wheel fit further onto the shaft where it should and makes the motor work like it should.

Posted on Feb 15, 2009

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 5 achievements.


    An expert whose answer got voted for 20 times.


    An expert who has answered 20 questions.

  • Expert
  • 118 Answers

You have to sync the limit switch with the trolly. Take the small white piece off the bottom of the gear and sprocket assembly. Rotate the center screw on the limit switch until it is all the way up. Put the chain back on the sprocket with the trolley in the up position. Put the small white piece on the bottom of the gear and sprocket assembly. Operate the opener with the trolley dissconnected from the door. You will have to adjust the limit screws on the side of the opener accordingly.

Posted on Feb 14, 2009


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya Repairman can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repair professionals here in the US.
click here to Talk to a Repairman (only for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

With my door closed, i push door button to open and the chain and opener continues inthe closing mode. any help?

Shop for sears craftsman liftmaste... on Google

Garage Door Opener Gear...
Sears Parts D... Liftmaster 41C4220A Ge...
Preferred Do... Chamberlain/l... Sprocket, Gea...
eBay Direct Replacement f...
Moving Up G... Liftmaster 41c4220a gea...
North Shore... Search Results

    Liftmaster Gear And Sprocket Kit 41c4220a Chamberlain ...

    Searsmore info. + -. Chamberlain LiftMaster 41C4220A Gear & Sprocket Assembly Kit. $31.40 ... Chamberlain Sears Craftsman Liftmaster 41A2817 Gear Kit. $27.65 ...

Jan 10, 2016 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

Sears Garage door opener #41A3625, chain sprocket hanging on the bar. I went to open the door this morning it was frozen and it didnt open. i went out to see why and i saw the chain hanginging, and the...

It sounds like the shaft for the sprocket and drive gear has broken or been sheared off. The part number for this assembly is 41C4220A and is available from Sears parts or any good local door opener company. It comes with instructions if you want to do it yourself.

Jan 03, 2012 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

The chain came off my Craftsman 53920 garage door opener. How can I fix this problem?

When a chain comes off it is an indication of another problem. The bearing on the sprocket shaft is bad and lets the sprocket lean forward and the chain pops off. The part number you need is 41C4220A Gear and Sprocket Assembly. The chain can be loosened by the nuts on the trolley.

Sep 11, 2010 | Sears Craftsman LiftMaster Chamberlain...

2 Answers

The sprocket snaped as garagedoor was comming down how to repair it

The sprocket and gear assembly is available at any good door service company. The part number is 41C4220A and comes with instructions.

Mar 18, 2010 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

Craftsman Garage Door Opener Model# 13953919 not working.

Yes replace the entire assembly. The part number is 41C4220A Sprocket and Gear Assembly and is available at Sears or any good door opener service company. It comes with instructions.

Jun 05, 2009 | Sears Craftsman LiftMaster Chamberlain...

1 Answer

The chain has come off the sprocket.

The gear/sprocket assembly needs to be replaced with part # 41C4220A. The top bushing is worn out that is why the chain fell off.

Dec 31, 2008 | Sears Craftsman LiftMaster Chamberlain...

2 Answers

Craftsman GDO Will not close

readjust the sensor controls on the side of the unit

Dec 28, 2007 | Sears Craftsman LiftMaster Chamberlain...

Not finding what you are looking for?
Sears Craftsman LiftMaster Chamberlain Garage Door Opener Wireless Keypad Model 976LM Security+ Logo

1,768 people viewed this question

Ask a Question

Usually answered in minutes!

Top Sears Building Materials Experts

Glenn Mayer
Glenn Mayer

Level 2 Expert

91 Answers


Level 3 Expert

4345 Answers

Cindy Wells

Level 3 Expert

5269 Answers

Are you a Sears Building Material Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides