Instructions for replacing your
chain drive garage opener
gear and sprocket assembly
|Parts typically used:|
41C4220A Gear/Sprocket assembly
41A3261-1 Dual Gear/Sprocket assembly
41A5585-1 Gear/Sprocket assembly
41A2817 Gear Kit
SPECIAL CONSIDERATIONS: The Liftmaster, Chamberlain, Craftsmen-Sears garage door opener gear drive replacement kits and/or assemblies come with instructions which may be adequate for some. However we decided to post our own supplemental instructions with much more detail.
IN ADDITION: It might be a wise idea to read these instructions completely before proceeding with your repair.
FINALLY: The instructions provided here were written for Liftmaster, Chamberlain and Craftsmen-Sears 1/2hp chaindrive garage door openers. Some of those principles can also be applied to Liftmaster, Chamberlain and Craftsmen-Sears 1/2hp beltdrive garage door openers.Liftmaster, Chamberlain and Craftsman-Sears also manufactures 3/4hp beltdrive and chaindrive garage door openers which are configured slightly different but the basic principles can still be applied.
Start by un-plugging the garage door opener. Go to the Trolley Assembly. Make sure the Trolley Release Arm is in the Manual Disconnect Position ( Figure Two ). Next loosen the chain. Use a 1/2" box wrench to loosen the Outer Nut counter-clock-wise ( Figure Three ). It may be required to hold the Inner Nut simultaneously in order to break loose the Outer Nut. Turn the Outer Nut counter-clock-wise until the threaded rod is flush with the edge of the Outer Nut. This will provide the required slack to remove the chain from around the sprocket.
Go ahead and hang the loose chain on the very back of the rail, on top of the garage door opener power head ( Figure Four ). Proceed by removing the light lens cover(s). Remove the outside cover with a 1/4" nut driver ( Figure Four ). Liftmaster, Chamberlain or Sears-Craftsman garage door opener covers will all have different appearances and/or configurations. Liftmaster garage door openers that look like the one in ( Figure Four ) will not require removal of the front light lens cover. Note: Be careful not lose the outside cover screws, put them in a safe place.
With full access to the internal components...This is a good time to remove the Limit Switch Assembly ( Figure Five ). The left and right tabs that are attached to the Motor Mount Bracket can easily be pushed in towards each other. The end of the Limit Switch Assembly should drop down. The single front hook of the Limit Switch Assembly should become easily removable. At this point let the complete Limit Switch Assembly hang from the brown, gray and yellow wires ( Figure Five ). Hint: The Limit Switch Assembly can be tied up out of the way. Remove the Limit Switch Retainer-Clip and Limit Drive Gear ( Figure Five ). Remove the Interuptor Cup Assembly ( Figure Five ). Unplug the RPM Sensor wiring harness. Be cautious with the RPM Sensor. Don't pull or tug on the RPM Sensor wires. Do not let the RPM Sensor hit or scrape against anything as you start to lower the Motor-Motor Mount Bracket. Removal and/or lowering of the Motor-Motor Mount Bracket will be explained in the next steps.
The next step provides two alternative methods. Notice there is STEP 4a and STEP 4b. STEP 4a is for those who wish to replace the Drive Gear or the Gear and Sprocket Assembly only. We have never seen the Worm Gear on the Motor Shaft strip or go bad as it's very durable. It becomes a judgement call in regards to replacing the Worm Gear. STEP 4b explains what is required in order to replace the Motor Shaft Worm Gear. To proceed with STEP 4b a few wires will need to be disconnected. This will be explained further on. Removal of the Motor-Motor Mount Bracket will make it easier to perform delicate operations on a work bench or stationary surface. Note: Be careful not to lose the screws during the next steps.
For STEP 4a a bungie cord, wire, twine and a 5/16" nut driver will be needed. First remove the Top Sprocket Cover if so equipped ( Figure Six ). Then proceed by removing the Motor Mount Bracket screws from the bottom ( Figure Six ). Next grab the complete Motor-Motor Mount Bracket and pull it down easy, from the Gear and Sprocket Shaft. A little wiggling, tugging and/or back and forth motion may be required to get it free. Be sure there is slack on the wiring harness. It's not really a good idea to let the Motor-Motor Mount Bracket hang by the wiring harness. Find a bolthole or other orifice on the Motor-Motor Mount Bracket as an attachment point. Use some twine, wire or a bungie cord on that end. Attach the other end to one of the back hang brackets or Motor Chassis ( Figure Six ). Feel free to get creative with securing the Motor-Motor Mount Bracket as this is not an exact science. Once the Motor-Motor Mount Bracket is secured, go ahead and use the 5/16" nut driver to remove the Gear and Sprocket Assembly screws from the bottom. Once all three screws are removed, lift the Gear and Sprocket Assembly from the top. Some models may have a black plastic Chain Spreader on the top of the chassis preventing the Gear and Sprocket Assembly from being removed ( Figure Nine ). If so equipped use a 1/4" nut driver to remove the Chain Spreader from the top of the Main Chassis.
For STEP 4b the RED, WHITE and BLUE wires leading into the Motor will need to be disconnected ( Figure Six ). This will need to be accomplished before removing the Motor-Motor Mount Bracket. One of the RED and BLUE wires will be connected to the Motor Capacitor ( Figure Seven ). The WHITE wire will be connected to the AC Line Terminal Block ( not shown ). Hint: Just follow the white wire coming out of the motor as it will lead to the terminal block. If these aforementioned wires are difficult to remove, use a pair of needle nose pliers to assist in their removal. Be careful not to damage the connectors. It's also important to remember where the wires will be reconnected. Next remove the top Sprocket Cover if so equipped ( Figure Six ). A 5/16" nut driver will be needed. Proceed by removing the Motor-Mount Bracket screws from the bottom ( Figure Six ). Next grab the Motor-Motor Mount Bracket and pull it down easy, from the Gear and Sprocket shaft. A little wiggling, tugging and/or back and forth motion may be required to get it free. Eventually the Motor-Motor Mount Bracket should drop down. Go ahead and set the Motor-Motor Mount Bracket on your work bench or clear work area. With the Motor-Motor Mount Bracket out of the way, go ahead and use the 5/16" nut driver to remove the Gear and Sprocket assembly screws from the bottom. Once all three screws are removed, lift the Gear and Sprocket assembly from the top. Some models may have a black plastic Chain Spreader on the top of the Main Chassis preventing the Gear and Sprocket assembly from being removed ( Figure Nine ). If so equipped use a 1/4" nut driver to remove the Chain Spreader from the top of the Main Chassis. At this point STEP 4a or STEP 4b should be complete. For those that opted for STEP 4a skip STEP 5 and proceed to STEP 6. For those that decided on STEP 4b...Proceed and complete STEP 5 before continuing on to STEP 6.
With the Motor-Motor Mount Bracket on a work bench or work surface, it's time to start the disassembly process. See ( Figure Eight ) for reference during this process. Go ahead and loosen the two 1/8" allen head bolts on the Retaining Collar. The Retaining Collar may side off easy or need to be pryed a little. The allen bolts on the Retaining Collar may have formed serrations on the Motor Shaft making the Retaining Collar difficult to remove. A little prying with a flat tip screw driver or prybar may be required. Once the Retaining Collar is removed, proceed by removing the Washer, Spring Washer and Bearing Washer. Filing down the Motor Shaft just enough to remove the serrations should make it easier to remove the Bushing and Worm Gear. Next remove the three 7/16" Motor Nuts from the Motor Studs. The Bushing should slide off the Motor Shaft at this point. Go ahead and remove the Motor Mount Bracket and Worm gear. The Motor Shaft has a Roll Pin that drives the Worm gear ( Figure Eight ). Some may opt to remove the existing Roll Pin and drive in the new Roll Pin provided in the kit. That choice is entirely up to the repair person. It was mentioned earlier in this write-up that we have never seen a Worm Gear fail, the same goes for the Roll Pin. Before reinstalling the Motor Mount Bracket and new Worn Gear, the Sprocket Shaft Bushing will need to be replaced ( Figure Eight ). A hammer can be used to strike the old Sprocket Shaft Bushing opposite the flange side. A pry bar or flat tip screw driver will help with the extraction by prying on the Bushing flange. When installing the new Sprocket Shaft Bushing a vise, press, hard plastic mallet or hammer with a block of wood can be used. The idea is to get the new Sprocket Shaft Bushing in without marking or scoring it up. Note: The Bushing and the Sprocket Shaft Bushing are different and not to be confused.
Once the new Sprocket Shaft Bushing is installed into the Motor Mount Bracket it's time to reassemble everything. Go ahead and place the new Worm Gear over the Motor Shaft and place the Motor Mount Bracket onto the Motor Studs. Put the Motor Nuts on the Motor Studs but leave the the Motor Nuts loose. Place the Bushing on the Motor Shaft and into the Motor Mount Bracket so the Motor Shaft can be centered onto the Motor Mount Bracket. The Bushing is not press fit and has a keyway that will only fit one way onto the Motor Mount Bracket. Next tighten down the Motor Nuts but be careful not to strip or break anything. There are no torque specs given for any of the fasteners. Now is the time to place the Bearing Washer, Spring Washer, Washer and Retaining Collar over the Motor Shaft and Bushing. Important: The long end of the Motor Shaft needs to be pushed out for maximum extension. Stand the Motor on end or push the Motor Shaft from the backside. Next go ahead and tightend down the 1/8" allen bolts on the Retaining Collar without stripping the allen heads. The Worm Gear and Motor Shaft should spin freely with absolutely no end play. Once the above procedures have been successfully completed in STEP 5, it's time to move on to STEP 6.
With STEP 5 complete it's time to reinstall the major components that were removed. The new Gear/Sprocket assembly will be the first component to be installed ( Figure One ). It will drop in from the top. The three holes on the Gear and Sprocket Assembly will line up with the threaded holes in the Main Chassis ( Figure Six ). The screws saved during the removal of the Gear and Sprocket Assembly will be reused. Use a 5/16" nut driver to attach the Gear and Sprocket Assembly to the Main Chassis. Once attached apply the supplied grease from the kit liberally on the Drive Gear. Apply a little bit of grease on the Sprocket Shaft or Sprocket Shaft Bushing ( Figure Eight ). Remove the Limit Switch Drive and Retainer ( Figure Five ).
Now it's time to reinstall the Motor-Motor Mount Bracket onto the Main Chassis. Lube the Worm Gear with the supplied grease before hand. The Sprocket Shaft will go thru the Sprocket Shaft Bushing on the Motor Mount Bracket. It should slide up smoothly, however it may be required to push-up, rock and twist a little inorder to get the Motor Mount Bracket flush with the underside of the Main Chassis. Be careful not to damage the RPM sensor. There are two holes on each side of the Motor Mount Bracket that need to line up with the threaded holes on the Main Chassis. The screws kept during the removal of the Motor-Motor Mount Bracket will be reused. Use a 5/16" nutdriver to attach the Motor-Motor Mount Bracket to the Chassis. Be sure not to pinch any wires during the process.
Reinstall the Limit Switch Assembly by hooking the single tab into the Main Chassis Slot. Now push the Limit Switch Assembly up so the left and right locking tabs are securely affixed to the intersecting Main Chassis Slots provided. Put a small dap of grease on the Limit Switch Drive Gear. Reinstall the Limit Switch Drive and Retainer onto the Sprocket Shaft. Reconnect the RPM Sensor Plug on the RPM Sensor. Reinstall the Interuptor Cup onto the end of the Motor Shaft. See ( Figure Five ).
This fourth paragraph of STEP 6 is very important. What will be explained here is how to sync the motor in relation to the position of the garage door. In between the redlines ( Figure Ten ) shows the Innerslide and Detachable Trolley connected together. During STEP 1 ( Figure Two. ) it was explained how to pull the Emergency Release Handle, on the Detachable Trolley, putting it into the LOCKOUT POSITION or manual mode. This needs to be done if it hasn't been done already. At this point the garage door opener needs to be plugged back in to it's power outlet. A working remote control will be required. Go ahead and press the remote control button so the motor will run. The Drive Sprocket must turn in the Clockwise direction as illustrated in ( Figure Nine ). The motor must run the Drive Sprocket in Clockwise direction until it stops. Now unplug the garage door opener from it's power outlet. Manually close the garage door. Notice where the Detachable Trolley and garage door push arm are located once the door is closed. Next manually grab the chain where it's tied up or hanging on the back of the rail ( Figure Two ). The chain will need to be pulled and reeled by hand in order get the Innerslide lined up with the Detachable Trolley ( Figure Ten ). This is how to get everything back in sync. If everything is off just a little bit that's ok, it can be fine tuned with the Travel Limit Adjustment Screws later ( Figure Fourteen ). Go ahead and install the Chain by physically placing it over the Drive Sprocket teeth. STEP 7 will explain how to adjust and tighten the chain inaddition to making the open and close travel adjustments.
STEP 1 mentioned turning the Outer Nut counter-clock-wise until the Threaded Rod is flush with the edge of the Outer Nut ( Figure Three ). If STEP 1 is already done there should be enough slack to install the Chain around the sprocket. Some Liftmaster, Chamberlain or Craftsman garage door openers utilize Dual Sprockets as shown in ( Figure Eleven ). The 8-Tooth Sprocket will run at a faster speed of 7 inches per second. The 6-Tooth Sprocket will run at a slower speed of 6 inches per second and also provides a little more torque. For One Piece California style Tilt-up garage doors it is recommended to use the smaller 6-Tooth Sprocket for the extra torque and smoother operation. For heavier Sectional and/or Carraige House garage doors the smaller 6-Tooth Sprocket is the better choice. For most Sectional garage doors the 8-Tooth Sprocket is sufficient. For Liftmaster, Chamberlain or Craftsman garage door openers that are and were equipped with a single Sprocket, they will work just fine as they have for many years. The dual Sprocket design was originally manufactured and sold for the California market because of the One Piece California style Tilt-up garage doors.
The next part of the process here in STEP 7 is to install the Chain Spreader if your garage door opener is equipped with one ( Figure Nine ). There is a slot in the Chain Spreader that fits over the verticle part of the T-Rail ( Figure Nine ). In addition there will be two small threaded holes in the Main Chassis where the Chain Spreader was originally attached. The Chain must be pulled around the Chain Spreader while simultaneously fitting the Chain Spreader onto the Main Chassis. Illustrated in ( Figure Eleven ) it shows a side view of how the Chain fits around the Chain Spreader, in relation to the 6-Tooth Sprocket vs the 8-Tooth Sprocket. A 1/4" Nut Driver will be used to snug down the # 8 x 1" Hex Screws and Washers from the top of the Chain Spreader. Next the Chain will need to be set for proper tension. Turning the Outer Nut clockwise on the Threaded Rod ( Figure Three ) will take the slack out of the Chain. Illustrated towards the right part of ( Figure Ten ) it shows Approximently 1/2". This is the space from the bottom of the Chain to the protruding edge of the T-Rail. The object is to not have the Chain to loose or to tight. The chain shouldn't be dragging on the T-Rail or Detachable Trolley. The chain should be adjusted with a slight amount of slack. If the Chain is slightly on the tight side it may tap up against the verticle part of the T-Rail. Once the desired Chain tension is obtained the Inner Nut and Lock Washer will need to be snugged down ( Figure three ). Two 1/2" open-end/box wrenches will be needed, one to hold the Outer Nut and the other to tightend down the Inner Nut and Lock Washer. A side view of the final product will be similar to ( Figure Ten ). Illustrated in ( Figure Twelve ) is different view of the garage door opener with the Chain installed on the smaller 6-Tooth Sprocket.
At this point everything should be back together with the proper chain tension. The fourth paragraph of STEP 6 explained how to basically sync the motor in relation to the position of the garage door. If those procedures were followed accurately the overall sync should be close. However it is likely that the Up and/or Down Limit Travel will need fine tuning. The illustration in ( Figure Thirteen ) shows the Limit Travel Adjustment Screws and Adjustment Label. The Limit Adjustment settings regulate the points at which the door will stop when moving up or down. Notice the large curved arrows that wrap around the Limit Adjustment Screws. A medium sized flat tip screwdriver is used for making adjustments. One full turn of either Limit Adjustment Screw in either direction equals 2" ( 5 cm ) of Trolley travel.
Before making any adjustments lets see how far the garage door travels up and down. The outside cover can be reinstalled on the garage door opener at this time or left off until all adjustments are complete. With the cover left off the garage door opener will run cooler until all adjustments are complete. However it might be easier to see which Limit Travel Adjustments need to made with the cover installed ( Figure Thirteen ). Make sure the Trolley is in the MANUAL DISCONNECT POSITION or automatic mode as illustrated in ( Figure Two ). Plug the garage door opener power plug into the power outlet. Use a garage door opener remote control button to activate the garage door opener. For sectional garage doors the garage door opener should lift the garage door Trolley approximently two to four inches from the Lens Protection Cover Bolt as illustrated in ( Figure Thirteen ). For One Piece Tilt-Up garage doors see ( Figure Fourteen ). If the garage door opens to far, turn the right Up Limit Adjustment Screw in the direction opposite the arrowhead. If the garage door doesn't open far enough turn the right Up Limit Adjustment Screw in the same direction as the arrowhead. Remember one turn equals 2" ( 5 cm ) of Trolley travel. Now go ahead and press the garage door opener remote control button again to run the garage door opener into the close position. If the garage door touches the ground and reverses, that means the garage door opener is closing the door to far. If that is the case it will be required turn the left Down Limit Adjustment Screw in the direction opposite of the arrowhead. If the garage door doesn't close all the way it will be required turn the left Down Limit Adjustment Screw in the same direction as the arrowhead. Once again one turn equals 2" ( 5 cm ) of Trolley travel. Keep making the adjustments needed until the desired garage door limit travel is obtained.
Note One: Run the garage door opener though a complete travel cycle after each adjustment.
Note Two: Repeated operation of the garage door opener during adjustment procedures may cause the motor to overheat and shut off. Simply wait 15 minutes for the motor to cool down and try again.
After replacing the Gear and Sprocket it's usually not a bad idea to check your Force Adjustments. The Force Adjustment Controls are illustrated in ( Figure Fifteen ). Notice the numbers 1 thru 9 on both Force Adjustment dials. The lower the numbers mean more sensitivity and less power while the higher numbers mean more power and less sensitivity. The idea is make sure the garage door will reverse when interrupted by an obstruction. To test this grab the bottom of the garage door on its way down to see if it reverses fairly easy. If the garage door doesn't reverse, this can be remedied by lowering the number on the left Down dial as illustrated in ( Figure Fifteen ). On the Force Adjustment Controls there is also a right dial for the Up force. To check the Up force find a place on the garage door to pull down as the garage door is travelling in it's Up or opening the cycle. If the garage door doesn't stop fairly easy, set the right Up force dial to a lower number. All force adjustment are made with a small flat tip screwdriver. If the dial numbers are set to low on the Force Adjustment Controls, the garage door may stop prematurely before completing it's Opening or Closing cycle. If this occurs, turning the Force Adjustment Control dials to next highest number should solve the problem. There's a fine line between sensitivty and power. Settings and adjustments may need to be readjusted as the weather changes. Don't forget to reinstall the Sprocket Cover if your garage door opener is/was equipped with one ( Figure Six ).
Note One: When the garage door is opened and closed without garage door opener, it should be balanced and operate smooth without binding.
Note Two: Repeated operation of the garage door opener during adjustment procedures may cause the motor to overheat and shut off. Simply wait 15 minutes for the motor to cool down and try again.
If all eight steps have been successfully completed, congratulations on a job well down. The feeling of self accomplishment is priceless... Saving a few dollars isn't bad either.