Replacing a LiftMaster nylon drive gear --It's actually easier than you'd think!

It’s happened to a lot of us with garage-doors: Early AM, already late for work; you push the switch to open your garage and the motor turns but the gate only barely lifts –or not at all! $#¡+!!!!! Chances are, most likely the white nylon drive gear’s teeth have finally worn off. This usually happens after about 10 years or so, no matter how well-greased the gears were originally.

What do we do now? Call a repair-person and pay them at least $180 (or more likely $250+ (or a lot more “+”!)) to come out and fix the stinkin' thang? !!!HELL NO!!! You can fix this yourself for UNDER $30, AND it’s easy. I did it recently, and… if *this* ol’ High-Tech RedNeck (i.e. *me*) can do it, ANYbody can.

Search for the part on Amazon.com: specifically, part # 41A2817. Prices are around $13-$19. I got mine for around $18 INcluding shipping. All you need is the large (2”) flat white gear, its respective roll-pin, AND (IMPORTANT!) the tube/packet of proprietary silicone grease (but keep the other parts in the unlikely event you’ll need ‘em in years to come). You’ll also need a 5/32” punch (w/ a straight cylindrical “business end” and flat tip; tapered or cone-shaped will not work), a hammer, a 5/16” socket (deep-well; also I needed a short Xtension) & ratchet for the motor mounting screws, and a nut-driver (I forgot the size!) for 6 sheet-metal screws that hold the cover on. Oh yes, and you’ll need an A-frame ladder too (but I used the bed of my Silverado Z-71, har har!).

NOW: HERE’S HOW IT’S DONE (and UNPLUG the damn thang FIRST!!!):

1st, carefully remove the 2 white light-covers; they’ll just be in the way of the 2 end-screws. Remove the cover; it’s attached by 4 screws: 2 on ea. side and the aforementioned 1 on ea. end. You’ll prob’ly notice A LOT of plastic “snow” in the box; carefully blow/brush as much of it out as possible. Go ahead and remove the white plastic trident-shaped set-pin for the limit switch gear (and the gear itself); then remove the entire limit switch assy. itself by squeezing the 4 black plastic tabs inward, and it’s OK to leave it dangling by the wires (saves trying to remember how to reconnect it later!). Also, unplug the RPM sensor's 4-pin polarized connector to get it out of the way.

Next comes a rather tricky part: removing the lower roll-pin that holds the white plastic drive gear in place. You may need to rotate the shaft with Vice-Grips (or electronically by temporarily engaging the remote switch) some to get it into an optimal alignment to drive it out without damaging the other components. Carefully align the 5/32” punch with the roll-pin and hit it w/ the hammer –HARD!!!!! This is very important: You’re much LESS-likely to do any damage this way AND the pin will be out faster. The principle of inertia plays an important roll here; think of it this way: Imagine a flagpole with a heavy brass ball on the top. You’re trying to drive a nail through the pole. Repeated soft taps w/ the hammer may easily cause the flagpole to start swaying and eventually break whereas a few well-aligned sharp HARD blows w/ the hammer will drive the nail to its destination, and the flagpole’s inertia will protect it. Same applies to the garage-gate opener. Obviously, it’s ALSO important to make sure your punch is aligned and set in order to avoid any off-glancing blows that would damage the circuitry close-by! I did it, and it came out relatively easily (some other users on web forums have said they’ve had difficulty removing this pin though). Only problem was: @ 1st I wasn’t paying attention and drove out the TOP pin (WRONG!!! :-PPpPpPpPPppp). No problemo; I just re-set it and then drove out the bottom 1 ;-)

Next step is to remove the motor itself. Use the 5/16” socket to remove the 4 black mounting machine-screws. Hold the motor, especially when removing the final screw, so it won’t bang on your head!! I had to also temporarily loosen the capacitor mounting bracket and slide it a bit to access one of the motor screws. Other users have reported that, for no-longer than it takes to replace the drive gear, it’s perfectly OK to let the motor dangle by its wires (as long as it’s not 100 years old or more, har har! :-P ).

Now, slide off the old gear –or what’s left of it! IMPORTANT: Use ALL of the included grease to lube-up the new gear; this is what helps it “live” as long as it can!! If there’s any grease left over, use it on the motor’s worm-gear (and maybe a dabble on the little limit switch gear also). Install the new gear on the drive shaft and re-attach the motor, making sure the motor’s worm-gear engages with the teeth of the new drive gear. Also, make sure the black plastic indicator cap for the RPM sensor is still in place on the motor shaft and hasn’t become dislodged. After re-mounting the motor, pound the new gear’s lower roll-pin in place w/ the punch & hammer.

Basically by now we’re just reversing the original procedure: re-plug-in the RPM sensor, re-mount the limit switch assy., re-attach the limit switch gear & trident pin, replace covers, &c. Many users reported having to re-calibrate (READ the manuals –it may be a bit tedious but it's easy!) their doors after this “operation”, but I did this almost 3 weeks ago (early March 2011), and SO FAR it’s been working perfectly w/o need of recalibration.

GRATEFUL ACKNOWLEDGEMENTS: I especially thank doorguy06 for clear concise instructions and don2737 for more detailed instructions and excellent macro-photography.

It took me about 2 hrs. to conduct the entire operation. And about 1 hr. of that time was going to Lowe's to get a 5/32" punch. A caveat here: they had several differently-sized punches, but the 1 I wanted was only available as part of a set. Oh well, @ least now I have a set of good punches made by Bosch (the same co. that makes race-car & fighter-jet engine parts --and also made my Tassimo coffee maker, har har har!!).

…and now some final thoughts that entered my brain: Many users (including don2737) recommend buying the gear kit that includes the sprocket since this relieves the need for driving out the roll-pin. However, this requires locking down the door w/ Vice-Grips, de-railing the chain (and taping it into position and marking it w/ WhiteOut on both the chain & sprocket), disengaging the trolleys, removing the entire LiftMaster box from the ceiling and –for me anyway— MUCH more of a pain in the @$$ than just a few well-placed hammer blows. But, that’s just MHO :-) Check out the above links and choose which method will work best for you. The "roll-pin" itself is aptly-named: it's actually a small piece of high-tensile-strength sheet-metal rolled into a thin cylinder and holds itself in place by compression inside a hole machined in the drive shaft. As such, you'll need a punch with a straight cylindrical flat-tipped "business end" (as mentioned near the top) and not a tapered/pointed one because it needs to travel almost all the way through the drive shaft before the pin pops out. Also, since the pin is hollow, a pointed punch would actually expand it even more, making it impossible to drive completely through the hole. A 10d nail filed off bluntly-flat on the tip might work, but the punch is much better.

Best wishes and GOOD LUCK! :-)