Garage door problem: I have to repeatedly adjust the travel limits.


I have a Craftsman 1/2 hp screw-drive garage door opener. It was professionally installed in 2003 on a new garage door. Never had a bit of trouble with it (until now).
In the middle of January, my wife said "the garage door isn't closing all the way". Sure enough, it stopped about 3-4 inches short of closing. And, the arm mechanism would bang into the actual drive housing when it was fully opened.
"Ah, simple adjustment" I thought. I grabbed a screwdriver and adjusted the travel limits (lower and upper) and it worked fine. For about two weeks.
I noticed was, again, not closing completely and banging into the drive housing when opened. I adjusted the limits a second time. Looked good to me.
Three days later... I notice it's not closing all the way <grrrrr>...
The problem is happening more frequently. Obviously, my feeble attempts at adjusting the limits work only temporarily.
Could the opening arm be consistently 'skipping' on the screw drive? What else could cause the repeating adjustment problems? Anything I should check before I just call someone to take a look at it?
Thanks!
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Sounds like the gear on the limit assembly is stripping out (odd for a fairly new opener, but not on older ones) & that the assembly needs to be replaced.
Doordoc www.ActionDoor.com

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When it goes out of "alignment" it seems to stop about the same distance from the ground (3-4 inches) each time. The first thing I thought was maybe the arm was slipping along the drive shaft somewhere. I didn't think about the gearing stripping.
Can I just pop the housing off of this model to check this? Or, is it a more invasive procedure to get to these gears?

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CsB wrote:

I would also check to make sure the door is properly balanced and is not binding. Disconnect it from the opener and make sure it will open and close without binding and that it will stay fully closed and fully open without assistance.
--
Joseph Meehan

Dia \'s Muire duit
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I will do this tonight and report back with the results. Thank you.
wrote:

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Check if the door is properly balanced. Disconnect it from the opener, and pull it half-way down. Let go. Does it stay there? If so, it's properly balanced. If not, the springs require adjustment, best done by garage door techs.
My guess is that it is unbalanced & wants to go up, so the opener has to push harder to get it to go down.
Or, do all the rollers roll properly in the track? Maybe some are dragging.
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I'll check this tonight and report back. Thank you.

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Mark the position of your limit screws and see if vibration is causing them to turn on their own.
Well, I guess they wouldn't really be turning "on their own" if vibration was causing them to turn, but you know what I mean. Actually, if they WERE turning on their own that would be pretty scary! <g>
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DerbyDad03 wrote:

Switches are spring loaded. Some times spring breaks.
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I understand. I wondered this, also. The limit screws are fairly stiff and I need to adjust them almost the exact amount of turns each time (2+ turns). I'll look more closely and mark their positions to see if vibrations are causing the trouble.

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http://www.liftmaster.com/pdfdocs/114A3077.pdf Look on page 34 which shows the limit assembly (all the models are the same).
Vibration isn't going to cause them to move that much. As I stated earlier something is stripped or it may be the limit contacts are not snapped onto the threaded screws completely.
Doordoc www.ActionDoor.com

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Another thought, the "rack" part #4 of the rail assembly on page 33 may be stripping & getting out of position on the screw, which would throw the limits off. If it changes suddenly I would suspect this part would be the problem more then the limits. If the limits are moving it would probably be a gradual change.
DoorDoc www.ActionDoor.com

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Thank you for everyone that offered ideas. Here's what I figured out.
My garage door opener is a Craftsman Model 139.53992 – ½ hp screw- drive.
I disengaged the trolley latch from the screw drive and tested the door. It moved freely without binding. It would stay fully closed and opened without assistance. If I opened the door 1/2 way up and let go, it did pull back to the closed position. If I opened the door 2/3 the way up it would balance and stay stationary.
I then disassembled the housing to look at the mechanics. As a future note to others disassembling this opener, to take the housing off you: (1) Open the light lens. (2) Remove bulbs. (3) Remove the two screws holding the cover to the bracket – these are in the upper corners of the bulb area. (4) Pull the cover *forward* (toward the lens) and remove. If you pull it downwards, you’ll brake the tabs on the rear plastic piece (like I did). It just wouldn’t be a home job if I couldn’t use duct tape in the repair. Check that one off. 
I was surprised at how simple the mechanism was. There are two gears on the motor. The first is a gear that engages a belt which then drives the screw. The second is a worm gear that engages the limit switch assembly.
I immediately noticed the gear on the limit switch assembly was barely engaging the worm gear on the motor shaft. I could gently apply pressure to the limit assembly gear and it would “jump” downwards and turn. Neither gear looked to be stripped or worn. However, both gears were dry as a bone.
I also noticed if I applied very gentle pressure to the bottom of the assembly (pushing upwards) the gear would fully engage. I removed the assembly and cut a slim cardboard shim (from a 9v battery package). There are three holes in the main bracket where the limit assembly “clicks” into place. I put the shim in the bottom most hole and inserted the limit assembly back into the bracket. The gear now fully engaged and I could not force it to “jump” down and turn.
I didn’t have any heavy grease, so I grabbed a tube of silicone and lubed up the friction points on the limit assembly and where the assembly engages the worm gear on the drive motor. I hope this wasn’t a mistake. Is regular silicone compound OK to use in a situation like this? The door opened this morning (8+ hours after repair).
I appreciate everyone’s help and advice. Hopefully this will save someone else a repair call in the future. If it ends up this is not the fix, I’ll post an update.
Thanks!
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