Liftmaster and Sears Craftsman brand openers are manufactured by the Chamberlain Co. They are all pretty much the same as far as functions and internal parts. Craftsman remotes don’t work with Liftmaster openers and vice versa.

When the motor is running and the chain or belt doesn’t move that means that the gear and sprocket has broken or the plastic gear has stripped its teeth. If the chain or belt is intact than its the plastic gear. If the chain or belt is sagging real bad or lying on the floor than the sprocket on top of unit has sheared off. If the gear teeth are stripped than this is caused by excessive weight of the door will strip the gear. This is common with a door that is out of balance or garage door has a broken spring and homeowner doesn’t know because the opener is opening the door. If the sprocket has sheared off than whoever installed the opener made the chain or belt too tight and this puts unnecessary pressure on the sprocket.

professional door technician is needed here…

All of these situations need a gear and sprocket replaced by a professional door technician. When it comes to Liftmaster or Craftsman openers this is the most common malfunction with this unit. It is an easy fix and should cost $200 or less to repair. I usually always have at least one replacement kit on my truck.

Replacing the gear and sprocket kit is not that difficult but there other factors with the opener that need to be considered when you replace them that you should not attempt yourself.