Replacing a Garage Door Opener Chain Drive Module

I have two garage doors with chain type garage door openers. This part has broken once on each door. The first door had the main spring break and the weight of the door caused the sprocket to brake off. The second door had the sprocket just brake off. My garage door openers are Chamberlain Liftmaster Professional 1/2 HP, but I think there are other brand garage door openers that share the same design. You will know if your chain drive sprocket has broken off if your door opener makes noise but the door stays closed, if the chain is slack and hanging down, and if you find the broken off sprocket on top of the opener or on the floor.

Step 1: Safety

SEVERE INJURY OR DEATH is mentioned three times in the instructions that came with the replacement part. If you are not comfortable with your abilities, you should have a professional garage door technician repair your garage door opener. On the other hand, if you are confident in your abilities and are willing to risk SEVERE INJURY OR DEATH, then by all means proceed ahead.

Before working on the garage door opener, make sure you isolate the electrical energy by tripping the breaker or, unplugging the garage door power cord.

Make sure the garage door main spring is in good shape and adjusted properly.

Step 2: Tools

The tools I used were a 1/4" nut driver, a Philips screwdriver, a slotted screwdriver, a ratchet with a 5/16" socket, a 1/2" wrench, and a step ladder. I also wore safety glasses.

Step 3: Supplies

I got a kit from Amazon for $19.56. It included the chain drive module and some extra parts that I did not need to replace like a drive screw and some bushings.

Step 4: Remove the Opener Cover

There are three Phillips screws holding on the garage door opener back cover. The top two only need to be loosened, when you take out the bottom screw, the cover will slide down. You can just let the cover hang by the wires plugged into it. This should give you room to replace the chain drive module.

Step 5: Take Out the Screws

There are three screws holding the chain drive module to the body of the opener. They have 5/16" hex heads.

Step 6: Remove the Bottom Gear

The chain drive module has a gear on the bottom that has to be removed both to take out the old module and before installing the new module. The small gear is held on by a plastic pin that goes thru the shaft. This plastic pin has two tabs that you have to pull gently to the side to allow the pin to slide out. Once this pin is out, the gear slides off the shaft.

Step 7: Install the New Module

After you take the small gear off the bottom of the shaft, you can install the new module. To make it easier to reinstall the small gear and it's retaining pin, orient the hole for the pin in the shaft so that you can see it.

Step 8: Reinstall the Small Gear

Reinstall the small gear on the shaft by placing it on the shaft and inserting the retaining clip.

Step 9: Reinstall the Screws

Reinstall the three screws that hold the module to the body of the opener.

Step 10: Put the Cover Back in Place

Slide the cover back on the top two screws and then tighten the bottom screw and then the top two screws.

Step 11: Loosen the Chain on the Trolley

To have some slack in the chain, to be able to put it back on the sprocket, you will need to loosen the nut on the end of the bolt, at the end of the chain, that attaches it to the trolley.

Step 12: Place the Chain on the Sprocket

Put the chain on the new sprocket. Some garage door openers are different, but I made sure that mine was in the door lowered position and the trolley was attached to the door in the down position.