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Liftmaster garage door only opens and shuts a few inches after gear replacement

Liftmaster garage door only opens and shuts a few inches after gear replacement

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  #1  
Old 01-12-13, 08:25 AM
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Liftmaster garage door only opens and shuts a few inches after gear replacement

I just changed out the gears with a replacement kit from Amazon. Kit shown below.

After I replaced the hears I hung the garage door opener. Now I'm having and issue where the garage only opens a couple inches and then closes a couple of inches and stops. . The safety sensors are hooked up and the light doesn't blink so I don't think that's the problem. The issue happens if my chain is connected or not so that should eliminate issues with unbalanced doors etc. I posed a video of how the gears are reacting when I hit the button.

Any clue what might be going wrong?

http://www.youtube.com/watch?v=69HiJtohmYA
 
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  #2  
Old 01-12-13, 11:59 AM
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Just to review a few basics, have you disconnected the door from the drive and opened and closed it by hand? It should work smoothly and balance about half closed.

Have you adjusted the force and limit controls and does that make a difference?

If you don't have an owners manual, Liftmaster has them on line.

Your unit model number would help us to help you.
 
  #3  
Old 01-12-13, 01:34 PM
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I got it to work. I turned down the torque controls to 0 and that caused the issue.

It works when I turned them up, but I noticed I have to turn them to 9kg (max setting) to get the garage to open and shut correctly. Isn't doesn't seem write. Any clue what may be causing this?
 
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Old 01-12-13, 02:03 PM
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And the garage does open and close easily by hand and will stay when it's half way up the track.
 
  #5  
Old 01-12-13, 02:24 PM
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You may have a heavy door. In your climate, heavier doors are the norm to keep garages semi warm in winter. That may account for the high setting. If it works, don't fix it.
 
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Old 01-13-13, 11:49 AM
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make sure the black wheel on the end of the motor shaft is tripping the rpm sensor. it has to be seated all the way on the motor shaft. make sure the rpm sensor is plugged in correctly.

http://ecx.images-amazon.com/images/I/41lBzCUtRdL.jpg
 
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Old 01-16-13, 09:59 AM
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rpm sensor

According to your video the rpm sensor does not have the fins of the plastic piece on the drive shaft going between the sensor posts. If the black plastic piece is seated all the way on to the shaft then you may need to re-check the installation of all of the pieces of the worm gear and make sure that all of those are seated correctly. Whenever the trolley only moves about 6 inches and goes in reverse without the lights flashing it is almost always the RPM sensor. Make sure to get those fins going through the two posts and your problem should be solved.
 
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Old 01-16-13, 06:12 PM
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"According to your video the rpm sensor does not have the fins of the plastic piece on the drive shaft going between the sensor posts.

if you look closely it looks like he has a lock collar where it shouldnt be.
 
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Old 01-17-13, 01:09 PM
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I could not get the video to go full screen so it was hard for me to see. But I was able to tell that the rpm sensor was not able to read the rpms.
 
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Old 11-26-13, 02:29 PM
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Did you get it fixed/working

I have the same problem. Changed out the whole worm gear and sprocket. And now the door moves just about 6 inches then reverses. I checked the black cover that looks like the rpm sense thing, and it moves out when the motor engages. Anyone else have that problem? I guess I'm going to have to pull it apart again and put it back together.
 
  #11  
Old 01-28-14, 12:54 PM
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? RPM sensor repair ???

I also just replaced the exact same gears and after proudly reassembling everything efficiently found that the door will only move a few inches.

With the chain disengaged from the door the same thing - the chain moves almost exactly six inches towards the closing position, then reverses.

I've examined everything else I can think of: adjusted the up & down force, made sure the safety systems are in good order, made sure the contacts are in good shape. I've been at a loss, until I read here about the possibility that the rpm sensor may be a problem. Does anyone know what I can do to solve this? I'd sure appreciate some advice.
 
  #12  
Old 01-28-14, 01:04 PM
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sounds like rpm sensor. it's on the end of motor shaft. 4 pin connector.
 
  #13  
Old 01-28-14, 04:25 PM
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RPM Sensor

Yep, that was it. I have two garage doors and looked at the other opener in operation. Apparently I didn't have the shaft bearings on tight enough so that the shaft would move in and out causing the interrupter cup to move outside of the sensor, thus making it unreadable.
 
  #14  
Old 01-30-14, 07:26 AM
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RPM sensor - problems figured out!

Solved the RPM Sensor problem!

I was confused by what could cause so many problems with the RPM sensor just from changing a gear! It seems that it is very easy to bump the spinning cap causing it to not work properly, but when I shoved mine back to where it was supposed to be, I still had the same problem - it seems there's more than one way to screw up this little thing!App

I got to looking around and found that a very small blob of grease from the bearings landed on the sensor (two little rectangular modules that the plastic cap rotates through). Apparently it flipped off the gear when it first spun up. This blocked the light, making the sensor not work. A few minutes of careful clean-up, and the system was working perfectly!
 
  #15  
Old 12-16-14, 02:01 PM
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Same Issue = RPM Sensor

After 14 years, I needed to replace the two internal plastic gears in my Lift Master 1/2 HP. The door worked fine for the next 4 months. However, it started closing 6" to 12" and then reversing. I disconnected the door from the chain and the door moved fine up and down. I checked and cleaned all the safety sensors, played with the limited controls/screws and turned the pressure settings to full. I was stumped....until I got to this thread. Thank you "do it yourself" for this website and thread. I had no clue about an RPM sensor. While the black coder cap was between the sensor, I found white plastic dust had gathered over the sensor. Once cleaned and assembled, the door is working again. I could not understand why the door worked for 4 months before it developed this issue. Nothing more than the cost of a cleaning wipe for my fix. Thanks everyone for your posts above.
 
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