June 1, 2013

How to replace a chain-drive garage door opener drive and worm gears

By Lyle Weischwill
How to replace a chain-drive garage door opener drive and worm gears

This DIY repair guide explains how to replace the drive and worm gears on a chain-drive garage door opener. The worm gear, which attaches to the motor shaft, meshes with the drive gear to spin the sprocket and drive the chain to open and close the garage door. If the gears break or strip, the door won't move. Replace a broken or damaged worm and drive gear with the manufacturer-approved replacement part.

Use this procedure to replace the drive and worm gears in Craftsman, Chamberlain and LiftMaster chain-drive garage door openers.

Quick links
Tools required
Step ladder
Allen wrench set
Hammer
Punch set
Emery paper
Work table
Socket wrench set
Slot screwdriver
Work gloves
Repair difficulty
Time required
60 minutes or less
Repair difficulty
Time required
60 minutes or less
Replacing the drive and worm gears on a garage door opener

This video explains how to replace the drive and work gears on a garage door opener.

Instructions

  1. 01.

    Disconnect power

    Use a step ladder to access the garage door opener’s power cord and motor unit.

    Unplug the garage door opener.

    Unplug the garage door opener.

  2. 02.

    Take the garage door opener down

    Position a work table near the area under your motor unit to hold the garage door opener during the repair.

    Pull the emergency release rope to release the trolley from the garage door.

    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. Use a helper if necessary.

    Open the light cover to access the wall control and safety sensor wires connected to the motor unit.

    Take a digital photo of the wall control and safety sensor wires connected to the motor unit. You'll refer to the photo later when reconnecting the wires.

    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 down and rest it securely on top of the step ladder.

    Climb down the step ladder, lower the motor unit down and rest it on your work table.

    Move your step ladder by the garage door so you can remove the rail from the header bracket.

    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.

    Tip: To avoid scratching a decorative garage door, remove the nuts, bolts and washers from the curved arm and carefully rest the curved arm against the door when disconnecting the garage door from the outer trolley.
    Tip: You may want to have a helper assist you when taking the garage door opener down.
    Disconnect the door arm from the trolley.

    Disconnect the door arm from the trolley.

  3. 03.

    Remove the chain and cable assembly

    Using a felt-tip marker, mark a link of chain and the sprocket tooth that meshes with it for when you reinstall the chain after replacing the drive and worm gears.

    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.

    Lay the chain out on the garage floor while you complete the repair.

    Disconnect the trolley threaded shaft.

    Disconnect the trolley threaded shaft.

  4. 04.

    Remove the gear and sprocket assembly

    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.

    Remove the screws from the motor unit cover and pull the motor unit cover off.

    Remove the plastic helical gear retainer and pull the helical gear off.

    Release the limit switch locking tabs by squeezing the sides just below the motor bracket near the helical gear.

    Move the limit switch aside and let it hang by its wires.

    Remove the gear and sprocket assembly mounting screws.

    Pull the gear and sprocket assembly out.

    Remove the mounting screws.

    Remove the mounting screws.

  5. 05.

    Remove the motor

    Remove the main bearing from the motor plate. Unplug the RPM sensor wire harness.

    Remove the interrupter cup from the motor shaft.

    Remove the motor mounting nuts from the front of the motor plate.

    Pull the motor out of the motor plate and set it beside the motor unit.

    Pry off the motor shaft bearing retaining clip and pull the motor shaft bearing out of the motor plate.

    Note: On some models, you'll need to loosen the set screws on the set collar and remove the set collar from the motor shaft, then remove the washer cap, spring washer, flat washer and bushing from the motor shaft before removing the mounting nuts from the motor plate and pulling the motor out.

    Remove the mounting screws.

    Remove the mounting screws.

  6. 06.

    Replace the worm gear

    Use a punch and hammer to drive the front roll pin out of the motor shaft.

    Pull the worm gear off the motor shaft and clean the motor shaft using fine grit emery paper.

    Remove the O-ring, C-ring and spacer from the motor shaft.

    Install the new O-ring, C-ring and spacer on the motor shaft.

    Lubricate the worm gear with grease, then slide the new worm gear onto the motor shaft, engaging the rear worm gear notches on the roll pin.

    Reinstall the front roll pin.

    Tip: Some motors have the roll pin behind the worm gear on the shaft so you pull the worm gear straight off.
    Remove the worm gear roll pin.

    Remove the worm gear roll pin.

  7. 07.

    Reinstall the motor

    Install the new motor shaft bearing into the motor plate and reinstall its mounting clip, using socket to push the mounting clip against the motor plate.

    Push the motor into the motor plate and reinstall the motor mounting nuts.

    Reinstall the interrupter cup on the motor shaft.

    Apply grease to lubricate the new main bearing and install it in the motor plate.

    Reconnect the RPM sensor wire harness.

    Note: For motors with a set collar, push the new bushing onto the motor shaft and slide it against the motor plate, engaging the notch on the bushing in the slot on the motor plate. Install the new flat washer, spring washer and washer cap on the motor shaft. Slide the new set collar against the washer cap on the motor shaft. Hold the set collar stationary and push the motor shaft through the set collar from the back of the motor to eliminate shaft play, then tighten the set screws.

    Reinstall the motor.

    Reinstall the motor.

  8. 08.

    Replace the drive gear

    Use a punch and hammer to drive the roll pin out of the drive shaft.

    Pull the drive gear off the drive shaft.

    Slide the new drive gear onto the drive shaft and line up the mounting hole in the drive gear with the hole in the drive shaft.

    Insert the new roll pin through the gear and drive shaft. Drive the roll pin into place using the punch and hammer.

    Lubricate the new drive gear with grease.

    Remove the drive gear roll pin.

    Remove the drive gear roll pin.

  9. 09.

    Reinstall the gear and sprocket assembly

    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 gear and sprocket assembly.

    Reinstall the gear and sprocket assembly.

  10. 10.

    Reinstall the limit switch and motor unit cover

    Position the limit switch on the motor bracket and snap the limit switch into place, engaging the limit switch drive gear with the helical gear.

    Reinstall the motor unit cover and secure it with the mounting screws.

    Reinstall the light bulbs and light bulb covers.

    Reinstall the chain spreader, securing it with the mounting screws.

    Reinstall the limit switch.

    Reinstall the limit switch.

  11. 11.

    Reinstall the chain

    Making sure not to twist the chain, thread it through the chain spreader and around the motor unit sprocket, matching the marked chain link to the marked tooth on the motor sprocket.

    Thread the inner nut up to the top of the trolley threaded shaft and reinstall the inner lock washer on the threaded shaft.

    Insert the trolley threaded shaft into the trolley hole and reinstall the outer nut and lock washer. Hand-tighten the outer nut.

    Tip: Have a helper push the inner trolley toward the threaded trolley shaft to apply more tension to the chain and cable, making it easier to thread the outer nut onto the trolley shaft.
    Reconnect the trolley threaded shaft to the trolley.

    Reconnect the trolley threaded shaft to the trolley.

  12. 12.

    Tighten the chain

    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.

    Tighten the chain.

    Tighten the chain.

  13. 13.

    Reinstall the garage door opener

    Reconnect the rail end to the header bracket using the clevis pin and fastener ring.

    Position your step ladder under the motor unit ceiling bracket and carefully set the motor unit on top of the step ladder.

    Climb the step ladder and 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. Using your digital photo for reference, 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.

    Tip: Reconnect the curved door arm to the straight door arm using the bolts, lock washers and nut if you disconnected the curved arm from the straight arm when freeing the garage door from the outer trolley.
    Reconnect the rail to the header bracket.

    Reconnect the rail to the header bracket.

  14. 14.

    Reconnect electrical power

    Plug in the garage door opener.

  15. 15.

    Adjust the travel limits

    Run the garage door opener through a complete travel cycle to check upper and lower travel limit.

    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.

    Tip: Repeated operation of the garage door opener during travel limit adjustment may cause the motor to overheat and shut off. Wait 15 minutes to allow the motor to cool and then continue adjustments.
    Adjust the travel limits.

    Adjust the travel limits.

Warning: Undertaking repairs or maintenance to appliances or power equipment can be hazardous. Should you choose to undertake repairs or maintenance, you are assuming the risk of injury to your person or property. In an effort to reduce the risk, use the proper tools and safety equipment noted in the applicable guide and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the repair. Some repairs or maintenance, however, should only be performed by a qualified technician.

Symptoms common to all garage door openers

Choose a symptom to see related garage door opener repairs.

Things to do: check garage door travel, tighten brackets and fasteners, test safety sensors, check travel limits and force limits
Main causes: garage door locked, damaged garage door tracks, up-force setting needs adjustment, RPM sensor failure, bad drive motor
Main causes: loose fasteners, broken brackets, need preventive maintenance, worn drive gears, loose or worn belt, loose chain
Main causes: faulty logic control board, bad RPM sensor, broken gears in the drive system, bad drive motor
Main causes: neighbor's remote programmed at the same time as yours, faulty wall control wiring, bad wall control unit
Main causes: garage door opener misaligned, travel limits need adjustment, bad travel limit switches, faulty logic control board
Main causes: safety sensor beams blocked, safety sensors not aligned, downforce setting needs adjustment, damaged garage door tracks
Main causes: radio interference, weak remote batteries, sunlight interference with safety sensor beams, safety sensors need adjustment

Repair guides common to all garage door openers

These step-by-step repair guides will help you safely fix what’s broken on your garage door opener.

June 20, 2016
By Lyle Weischwill
How to replace a garage door opener battery

The garage door won't move during a power outage if the battery is dead. Here’s how to replace it.

Repair difficulty
Time required
 15 minutes or less
How to replace a chain-drive garage door opener gear and sprocket assembly

Learn how to replace the gear and sprocket assembly on your garage door opener if the drive motor runs but the door won't move.

Repair difficulty
Time required
 60 minutes or less
How to replace a chain-drive garage door opener drive and worm gears

If your garage door won’t move, the drive and worm gears could be broken. This guide will help you replace the gears.

Repair difficulty
Time required
 60 minutes or less

Articles and videos common to all garage door openers

Use the advice and tips in these articles and videos to get the most out of your garage door opener.

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How to repair broken or damaged wires video

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