Gear replacement on Garage Door Liftmaster 1255R

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  #1  
Old 02-10-10, 08:19 AM
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Gear replacement on Garage Door Liftmaster 1255R

Hi,

My the "main" gear on my garage door has gone bad. I have read on this site several instructions on how to replace the gear and to be honest i am a little confused. Some say remove motor some say not to ......since i have not done such a thing i was wondering if someone had comprehensive instructions/pictures on how to do this job. I like to tinker/fix things but i would NOT say that i am good at it.
 
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Old 02-10-10, 09:29 AM
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I just replaced the drive gear on a sears craftsman garage door opener. I believe liftmaster makes them for sears, and they are essentially the same. I did not remove the motor. Heres what I did.

Close the garage door.

Unplug the unit so it has no power.

Remove the plastic sprocket cover on top of the unit.

Loosen the chain by loosening the bolt. Loosen it enough so that you can slip the chain off the sprocket

Remove the chain from the sprocket. Use a clamp on the rail to hold the chain from falling to the floor.

At the bottom of the sprocket assembly is a small plastic gear held in place by a plastic clip. The clip has 3 prongs, one that goes thru the center of the shaft and 2 that go around the outside of the shaft. Pull the clip straigt out, and remove the gear by pulling it downward.

The sprocket assembly is held in place by 3 cap screws that screw upward from the inside. Remove them. Space is limited and its a little time comsuming. A 1/4" rachet gets at one of the screws and a rachet with a long extension can get the other two.

After removing the screws, remove the sprocket assemby be pulling out from the top. Hopefully, you have enough room above to do this. I did. If not, you may have to drop the opener and rest it on top of a ladder.

The drive gear is held in place with 2 pins that go thru the center of the assembly. You only need to remove the lower one if you are just replacing the drive gear. You'll need to inspect the washers and other hardware at the top of the sprocket assembly to see if they need replacing as well. My did. If thats the case, youll need to remove both pins. You can knock the pins out with a punch. Its a pain in the a$$ to get them out, so take your time. My replacement parts came with new pins, but I reused the old ones.

Once you have the pins out, the plastic drive gear should slide down the shaft with a little persuasion. Replace the gear with the new one, lining up the pin holes in the new drive gear. Replace the pins. I used a hammer and small bolt to do this. There may be a better tool.

Apply the entire packet of grease to the new gear. Dont skimp, you want all the teeth on the gear to be totally coated.

Reverse steps above to reinstall the sprocket assembly etc. Hopefully you dont wind up with any spare parts.

Sorry, no pictures.
 
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Old 02-10-10, 02:55 PM
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Need help lifting out sprocket from Liftmaster garage door

To HeresJohnny or anyone else,

Johnny, your instructions are wonderful. I've done all that and more to remove the entire sprocket and replace with new one.
Problem is sprocket will not slide through the motor housing.
I've loosened everything but can't get it to budge.
Any advice?
Liftmaster Model 1250- 1/3HP

Also purchased just the plastic wheel. Trying to remove only the old wheel. Can't get the metal washers, etc off directly under the wheel, to begin to remove the bottom pin.
Yes, I've removed the retainer clip and drive gear.

Any advice with this? Pry apart with flathead and WD40? Worried the lubricant will make gripping round pieces impossible.

My goal is to replace the entire sprocket, not just the gear wheel. Worm gear is fine.
Waiting to use our garage again.
 

Last edited by Missy47; 02-10-10 at 03:12 PM.
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Old 02-11-10, 05:56 AM
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Missy

I suspect your opener is different than mine. I'm a tilesetter who happened to fix his garage door opener. Perhaps someone else with a lot more knowlegde can step in and help you.
 
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Old 02-11-10, 05:42 PM
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How long an extension did you need to use? The reason i ask is i dont have an extension but i can borrow one and i just need to know how long of one i will need.

Thanks.
 
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Old 02-13-10, 08:44 AM
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Liftmaster door won't budge after replacing sprocket and worm gear

Replaced the sprocket and worm gear correctly, noting all points from previous threads.
All good to go.
Door operated and raised. Thats it.
Now just hums clicking forward and reverse. The chain isn't moving. Light blinking 5 times.

Only thing I can notice different is the Chain trolley is closer to motor than should be; guess it got moved while reattaching. It almost touches a nut from the opener assembly. Is this the problem?

Should I remove the chain and rotate it until its in a better position?
About to scream.
 
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Old 02-15-10, 08:31 AM
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I just did this yesterday on my Liftmaster 1255R 1/2 HP opener. I bought the kit with the entire drive shaft already assembled. My large plastic sprocket was shredded. This kit has the output shaft with the large white sprocket already on it and the metal one that pokes out the top and drives the chain. It also contains the worm drive gear that goes on the motor output shaft and new bearings and spacers. It cost me $28 from EBAY. I installed all the new stuff and had to remove the motor to replace the work gear. Anyway, once I installed everything I did this to help with door travel adjustment:

- Have the door closed and make sure the trolley is locked to the door. This is how it would be if the door broke in the closed position. If not, close the door and slide the trolley all the way toward the door until it locks to the door. If you have the chain off the sprocket on the opener this is easy to do just be careful with the loose chain.

- With the chain still off the metal sprocket on the opener, plug in the opener and run it until the sprocket completes a clockwise cycle. Just watch the metal sprocket turn until goes clockwise and stops. This is how would act to close the door. If it spins counter clockwise and stops just push the button to run it again and it will turn clockwise and stop.

- Now connect the chain and tighten it.

- This gets you close to a decent travel adjustment. Now run the opener and make final adjustments with the 2 travel adjustment screws in the side of the opener.

In my case I had to reduce up travel because it was hitting the stop bolt that is about 6 inches from the opener. I also had to increase down travel a inch or so because it didn't completely close. Each turn of the travel adjustment screw results in 2 inches of door travel. This is for 1/4 HP and 1/2 HP openers. For a 3/4 HP opener it makes a 3 inch change.

These instructions came with the gear kit.

If this doesn't do it for you make sure you have the black cup installed on the end of the motor shaft and that the RPM sensor is installed and the wire connected to it. Also make sure the motor shaft is pushed all the way towards the rear of the opener. Hope this helps.
 
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Old 03-28-10, 07:04 PM
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printed instructions, photos, etc. to replace gear

I made a webpage that includes the instructions that come with the gear kit, how to re-set the door travel limits, lots of pictures, links to suppliers of the gear kits.
http://************/gearfix

 
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Old 03-28-10, 07:09 PM
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Link to page with the instructions

Hmm, must be some rule against posting the url. Try this

liftmaster_repair gear replacement


 
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