Commonly called a carriage, the trolley on your garage door is what connects the operating arm attached to the door to the overhead rail. It provides the pushing or pulling that raises or lowers the door with the automatic opener. Usually, it’s installed along with the opener, but occasionally becomes worn out or damaged and will need replace by itself. Here’s a brief guide on how to replace your garage door trolley.
Start by disconnecting the motor from the power supply. You’ll either need to unplug it — or if the opener is connected to a power outlet — flip the fuse in the powerbox it corresponds to.
Pull the release cord that connects the garage door to the trolley. Close the door by hand so that the trolley is a the outer end of the rail.
Position a ladder underneath the trolley. Remove the cotter pin connecting the trolley with a pair of pliers. Swivel the arm down so that it is even with the side of the door.
Undo the bolt connecting the the outer end of the rail to the wall bracket. Lift the rail so there is enough room to clear the carriage off the end of the rail.
Fit on the new replacement carriage onto the rail. Be sure the release cord at the underside is at the inner end toward the motor. Disengage the carriage by pulling on the cord, pushing the carriage towards the rail.
Reattach the rail to the wall bracket with the bolt and nut you started with. Swivel the arm back to reattach to the carriage. Replace the cotter pin.