How to Fix a Garage Door Chain Drive Sprocket


There are two sprockets on a garage door. One sits above the motor unit and the other is connected to the trolley. Both work in conjunction to pull the chain which moves the garage door up and down. If the chain is unable to move through the sprockets properly, it is twisted, misaligned or needs to be replaced. The sprockets themselves aren't motorized and don't become twisted or misaligned, but either could have loose nuts.

Things You'll Need

  • Ladder
  • Flathead screwdriver
  • Adjustable wrench
  • Close the garage door, and turn on the garage light.

  • Position a step ladder underneath the garage door motor. Unplug the motor from the power outlet located on the garage ceiling.

  • Pry the cover off the sprocket located on top of the motor unit with a flathead screwdriver.

  • Move the stepladder underneath the trolley, which moves the chain back and forth along the track. Loosen the inner and outer nuts securing the trolley to the track and holding the chain with an adjustable wrench. Once the trolley is loose, pull it down and remove the chain.

  • Pull the chain from around the motor unit sprocket.

  • Inspect the chain. If the chain is twisted, straighten it back out. If broken, replace it with the same size chain.

  • Guide the chain back around the motor unit sprocket. Make sure the chain holes line up with the holes in the motor unit sprocket, and all the chain's teeth are facing the side.

  • Rethread the chain around the trolley sprocket. Then retighten the nut that is facing the garage door to reconnect the sprocket to the track. Avoid twisting the chain as you tighten the nut. Retighten the trolley's inner nut once the chain is hanging 1/2-inch above the base of the rail at its midpoint. The sprockets on the trolley and motor will now operate properly.

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