How to Replace the Main Gear in a Garage Door Opener

It's 06:00 am and you are leaving for work. You press the garage door opener wall button and hear a subtle hum from your electric motor but the door failed to move. If your garage doors springs are intact chances are you garage door openers main drive gear has failed. You can easily inspect your drive gears by unPlugging your garage door opener and removing the metal cover. The main drive gear is made of a white plastic that typically is the weak link in the opener. Many things can cause this gear to fail. Some causes of wear are:

How to Replace the Main Gear in a Garage Door Opener

How to Replace the Main Gear in a Garage Door Opener

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How to Replace the Main Gear in a Garage Door Opener

How to Replace the Main Gear in a Garage Door Opener

or out of balance Garage door (Springs broke or in need of adjustMent)
or Chain to tight to
or Old age
or Excessive use or high cycle
or Factory defect or lack of grease at time of manufacture

Replacing the large white gear is acheap, quick and easy do it yourself repAir as long as you have a few simple hand tools and follow the safety precautions. These gears can be purchased online at a variety of levels of components.

Before you get started it is important for you to have a list of the few simple tools needed to accomplish this project:
or Hammer
or Half inch wrench or adjustable wrench or pliers
or 3/8 "Socket or Nut Driver
or 1/4 "Socket or Nut Driver
or 5/16 "Socket or Nut Driver
Standard or Flat Screwdriver
or 5/32 "Punch or similar

~ WARNING ~
To prevent possible SERIOUS INJURY or even DEATH from electrocution, ALWAYS Disconnect the power cord from your garage door from the outlet before proceeding with any inspection or repAir.

Step # 1
Make sureyour garage door opener is unPlugged. This step insures that no one unintentionally attempts to open or close the garage door while you are working on it or you do not accidentally activate the door while servicing it.

Step # 2
Disconnect the door from the outer trolley by manually pulling the disconnect red rope and manually close the garage door.

CAUTION
The Garage door MUST be in the fully closed position during all repairs and inspection.

Assuring that your garage door is closed will reassure that your door will not fall or make any moveMent that would cause injury or startle you. We recomMend that once the door is closed that you clamp the door down using a vise grip or clamp above one of the rollers to prevent the door from being opened from theoutside.

Step # 3
Slacken the chain tension belts or by losing the tension nut on the garage door opener trolley. Typically this is nut and can be adjusted with a .5 "wrench.

Step # 4
Remove the sprocket or belt pulley retainer cap. Usually this has a clip on the back if you press into it will release.

Step # 5
I always recomMend marking the position of the chain or belt to the sprocket prior to removing. This can easily be done with white out, tape or any other means. This step helps assure that your chain or belt gets reinstalled in the correct position and makes for quick and easy reference if needed later. Remove the chain from the sprocket or belt and then slide the inner trolley to the closed position until it engages the outer trolley. Place loosechain/belt on the end of the rail closest to the sprocket. I typically duct tape the chain to prevent it from falling to the floor and getting all twisted and dirty.

Step # 6
It is now time to remove both end covers and the main housing. The end cover are each attached by three or four .25 "head screws that can be removed with a .25" nut driver or socket. Be sure to unPlug the wire to the circuit board.

Step # 7
Remove the retaining clip and the drive gear for the limits. Also at this time remove the limit switch assembly by squeezing the sides just below the bracket by the drive gears. There is no need to disconnect the wires as it is ok to leave this limit assembly hang by the wires. Do not make any adjustments to the limit assembly screws, this willinsure that there is minimal adjustment needed to the limits after you complete your repair and run your garage door opener.

Step # 8
Now its time to remove the RPM sensor, this can be easily done by unPlugging the wire harness and remove the RPM sensor from the securing tabs.

Step # 9
Disconnect the red, blue and white wires from the motor. It is important that you note where these wires go. The same color wires go to the same terminals on the capacitor red/yellow and blue/blue.

Step # 10
Remove the four 5/16 "hex head screw's that hold the motor assembly to the frame of the garage door opener. Be sure to put your hand under the motor before removing the last screw to prevent the motor from falling. Slide the motor assembly off the drive shaft andplace in a safe place. (Not on top of the ladder for obvious reasons).

Step # 11
Remove the three hex head screws holding the sprocket assembly to the main chassis using a 5/16 "nut driver or socket. Now it is time to decide if you want to replace the main gear only or the enTire sprocket or all chain drive models 1984 to present.

Step # 12
Skip this step if you are replacing the enTire gear and sprocket or pulley assembly. If you are going to replace the drive gear support the drive shaft on a block of wood and drive the lower roll pin/Tension pin out with a 5/32 '' punch. See photo example below.

Step # 13
Remove and replace the worm gear. In most cases it is not necessary to replace the worm gear unless it shows signs of wear. If you wish to replace this gearremove the shaft collar with a 1/8 "hex wrench. Please be sure to note the location of each of these components as you disassemble so you can re-install in proper order. When you receive your gear kit, you will find there are parts not used in your model this is because these kits are universal and work with many models of Sears, Craftsman, Wayne Dalton, Liftmaster, Master Mechanic, True Value and other brands of garage doors openers. Only replace the parts that are used on your garage door opener. Remove the 3 nuts that hold the motor to the frame and then remove the worm gear. Install the new worm gear making sure the roll pin is properly seated in the new gear. Re-install other components in reverse order. After you complete this assembly I recommend you lube the worm gear so you donot forget.

Step # 14
Begin reassembly in reverse order. Be sure to thoroughly lube the main drive gear and that grease is on each and every tooth. Attach the gear and sprocket or pulley assembly to the main chassis with the three 5/16 head screws. Install the assembled motor frame to the chassis with the four 5/16 head screws and reattach the red, blue and white wires; now install the limit assembly and the limit drive gear making sure they mesh properly. You can now install the RPM sensor and reconnect wires. Install the metal cover and end panels, be sure to plug in the circuit board and reconnect photo eye and push button wires.

Step # 15
Reconnect the power cord to the opener and cycle the opener until the sprocket completes a full clockwise cycle. The trolleymust be in the fully down position before installing the chain. Now you can remove the tape from the rail and reinstall the chain. The chain and sprocket reference mark should be close to lining up. Tighten the chain so that the chain is .5 "above the base of the rail at midpoint for" T "style rails and .25 for square tube rails. Secure the chain tightening lock nut.

WARNING
Note when adjusting and testing your garage door motor it is important
to make sure no one is in the path of the moving door.

CAUTION
It is important to know when testing your garage door opener it is possible to over cycle the motor
and have the motor temporarily overheat and stop operating.
To prevent this try and not operate the door opener more than 10 cycles
without giving it 5-10 minutes to cool off

Step # 16
Now run the opener and test to see if the door opens to the correct position and closes to the correct position. If you need to make adjustments use the travel adjustments screws to make fine adjustments. I recommend only making slight adjustments .25 turn or less at a time. For reference one full turn of the screw equals approx 2 "of travel on .5 and .25 HP models and 3" on .75 HP models.

How to Replace the Main Gear in a Garage Door Opener