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

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Garage door problem: I have to repeatedly adjust the travel limits. CsB 01-31-2007
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Posted by doordoc@prodigy.net on February 1, 2007, 11:00 am


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

> 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.
>
>
>
>
> > Mark the position of your limit screws and see if vibration is causing
> > them to turn on their own.- Hide quoted text -
>
> - Show quoted text -



Posted by doordoc@prodigy.net on February 1, 2007, 12:18 pm


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

> 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.
>
> Doordocwww.ActionDoor.com
>
>
>
>
> > 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.
>
>
> > > Mark the position of your limit screws and see if vibration is causing
> > > them to turn on their own.- Hide quoted text -
>
> > - Show quoted text -- Hide quoted text -
>
> - Show quoted text -



Posted by CsB on February 2, 2007, 8:36 am


Thank you for everyone that offered ideas. Here's what I figured out.

My garage door opener is a Craftsman Model 139.53992 =E2=80=93 =C2=BD hp sc=
rew-
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 =E2=80=93 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=E2=80=99ll brake the tabs =
on
the rear plastic piece (like I did). It just wouldn=E2=80=99t be a home job
if I couldn=E2=80=99t use duct tape in the repair. Check that one off. =EF=
=81=8A

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 =E2=80=9Cjump=E2=80=9D dow=
nwards 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
=E2=80=9Cclicks=E2=80=9D into place. I put the shim in the bottom most hol=
e and
inserted the limit assembly back into the bracket. The gear now fully
engaged and I could not force it to =E2=80=9Cjump=E2=80=9D down and turn.

I didn=E2=80=99t 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=E2=80=
=99t
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=E2=80=99s 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=E2=80=99ll post an update.

Thanks!


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