Located at the top of the motor unit, the
gear and sprocket assembly drives the chain that connects to the trolley and moves the
trolley along the rail to raise and lower the garage door. A broken gear and sprocket
assembly won’t move the chain when the motor runs. If your gear and sprocket assembly breaks,
you can replace it using the steps in this video. Wear work gloves to protect your hands.
Now, let’s get started. Unplug the garage door opener. Or, turn off the house circuit
breaker for the garage door opener. Pull the emergency release rope to release the trolley.
Shut the garage door if it’s not already closed. Remove the fastener ring from the straight
door arm connected to the outer trolley. Pull out the clevis pin while supporting the straight
arm to disconnect the garage door from the outer trolley. Lower the straight and curved
arms down and rest them against the garage door. Open the light cover to access the wall
control and safety sensor wires connected to the motor unit. Disconnect the wall control
and safety sensor wires from the motor unit. Close the light cover. Remove the nuts, bolts
and lock washers that secure the motor unit to the ceiling bracket. Support the motor
unit with one hand as you remove the last bolt from the ceiling bracket. Carefully lower
the motor unit and rest it on your work table. Remove the fastener ring from the header bracket
clevis pin. Pull the clevis pin out of the rail and header bracket while supporting the
rail with one hand. Lower the rail and rest it on a rung of the step ladder so the rail
is level with the motor unit on your work table. Using a felt-tip marker, mark a link
of chain to help you reinstall the chain correctly later. Slide the outer trolley away from the
inner trolley. Remove the outer nut and lock washer from the trolley threaded shaft and
pull the threaded shaft out of the trolley. Pull the chain off the motor unit sprocket
and out of the chain spreader. Remove the light covers and light bulbs from the motor
unit. Remove the screws from the chain spreader and pull the chain spreader off the motor
unit. Flip the motor unit over. Remove the screws from all four sides of the motor unit
cover and pull the motor unit cover off. Remove the plastic helical gear retainer and pull
the helical gear off. Remove the gear and sprocket assembly mounting screws. Pull the
gear and sprocket assembly out. The mounting holes in the new assembly aren’t threaded.
Thread the mounting screws into the new gear and sprocket assembly to ease the mounting
process and then remove the screws. Apply grease to the plastic drive gear. Insert the
gear and sprocket assembly into the motor unit and install the mounting screws. Apply
grease to the helical gear. Push the helical gear onto the gear and sprocket assembly shaft
and secure it with the retaining clip. Reinstall the motor unit cover and secure it with the
mounting screws. Flip the motor unit over. Reinstall the light bulbs and light bulb covers.
Reinstall the chain spreader, securing it with the mounting screws. Making sure not
to twist the chain, thread it through the chain spreader and around the motor unit sprocket.
Thread the inner nut up to the top of the trolley threaded shaft and reinstall the inner
lock washer. Insert the trolley threaded shaft into the trolley hole, use channel lock pliers
to apply tension to the chain and cable, and reinstall the outer nut and lock washer. Hand-tighten
the outer nut. Adjust the outer nut to position the trolley threaded shaft so the chain hangs
about 1/4-inch above the base of the rail at its midpoint. Tighten the inner nut against
the trolley to secure the trolley threaded shaft. Reconnect the rail end to the header
bracket using the clevis pin and fastener ring. Carefully set the motor unit on top
of the step ladder. Reinstall the motor unit to the ceiling bracket using the nuts, bolts
and lock washers. Open the light cover to access the wall control and safety sensor
terminals on the motor unit. Reconnect the wall control and safety sensor wires to the
motor unit. Close the light cover. Reconnect the straight door arm to the outer trolley
using the clevis pin and fastener ring. Re-engage the trolley. Plug in the garage door opener.
Or, turn on the house circuit breaker. Run the garage door opener through a complete
travel cycle to check upper and lower travel limits. If the garage door doesn’t close completely,
adjust the down travel and cycle the door open and closed to test the adjustment. Continue
to adjust the down travel until the door closes completely. If the door doesn’t open completely,
adjust the up travel in the same manner.