Every year about this time we see a sharp increase in the number of drive gear and sprocket failures in garage door openers. We have customers asking "Can I get just the large plastic gear by itself?" Most of these customers have seen "cheap" aftermarket gears on the internet. Many of these gears are made in Venezuela or other aftermarket sources and include just the large gear and not the drive gear on the motor shaft. These will work for awhile but if put any value on your time you should always change both gears at the same time and be sure to lubricate them well.
It is our opinion that on Chamberlain manufactured systems that the complete repair kit (OEM) is much preferred. With the complete kit (the most common is 41C4220A for chain drives except 3/4hp) you get both gears, drive pins, motor and output shaft bearings, drive shaft with sprocket (chain or belt drive) and the lubricant. To save time the output shaft and large gear are preassembled. An experienced technician can usually change the complete kit in under 30 minutes. Be sure to give the garage door a good safety and maintenance check after installing the new parts. If you have not had your garage door serviced by a trained professional within the last couple of years why not take this opportunity to have the job done by a professional.
If you decide to change just the drive and motor gears be aware the the upper bushing on the output shaft many times fails soon after the plastic gears. If you see black shavings on the top of the large plastic gear then the upper busing is going bad. The only way to get this bushing is to replace using the complete repair kit so why not just do it right the first time and save the trouble of having to do the job again just to "save" a few bucks. If you don't then you will pay more and have to do the job twice.
The overwhelming majority of the residential garage door openers manufactured in the past 20 years have been manufactured by Chamberlain based in Elmhurst, IL. Chamberlain manufacturers garage door openers under the following names: Chamberlain, Liftmaster, Sears, Craftsman, Raynor, Craft Master, and previously John Greene (residential only). With the exception of units with a dc motor all of the residential garage door openers use nylon (aka plastic) drive gears and sprockets. The most popular part numbers are 41C4220A, 41A2817, 41A4885-2, 41A4885-5, 41C4770, 41A5658.
Garage Door Corporation is a Liftmaster (Chamberlain) Factory Authorized Dealer and uses only OEM parts and only recommends the complete repair kits. If you are in the Chicago, IL and suburban areas please contact us through our website at www.gdcorp.com for professional local service by trained technicians.