Question about Sears Craftsman LiftMaster Chamberlain Garage Door Opener Wireless Keypad Model 976LM Security+

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My garage door jumps about 3 or 4 inches and then moves smoothly when opening. I have disengaged the opener and run the door by itself and it runs smoothly. What I have noticed is that the top of the door flexes when the door is opening. It is like the opener is pulling the door backwards instead of up. When I open the door by lifting at the bottom this does not happen and the door run smoothly. Any assistance in sorting this out will be much appreciated. Thanks.

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  • John Soogrim Aug 27, 2010

    If the issue is the mounting of the motor itself why does the door flex? I did not mention that this is a belt drive unit not a chain drive one. Should the door have a metal brace across the top? I have seen those braces on some doors. My door is a 4 section wooden door.



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This is not uncommon on many openers.

When installed some contractors just use minimum bracing for the motor unit.

I tend to add a small amount extra. If you have the motor unit mounted directly to your garage roof then it should be fine but i that case I would be checking the gear chain wheel to ensure it is secure to the shaft
Do not put your fingers anywhere near the unit whilst testing and go for a visual inspection only !
Next ensure power to the unit is off and try work the gear to check for any play. If there is play then check the screws that lock the wheel to the shaft and the motor mounts

If it is suspended from the roof then add extra bracing on the diagonals to firm up the drop legs or even an extra brace out from the rear of the unit.

There are two schools of thought on this practise of extra bracing and it is not always recommended but from practical experience and long term usage I have found it to save money.


Posted on Aug 27, 2010

  • Project NOMAD
    Project NOMAD Aug 27, 2010

    The door should not really flex especially in the middle as this tends to try and pul the guides inward slightly.

    That would cause the small **** you see as the drive has to pull a little harder to overcome the bit of resistance

    I have seen older (better built) wooden doors that DONT need a top brace simple because they used better materials.

    Most GOOD metal doors dont need them either as the way the metal is folded give it a strong edge from which to pull

    cheaper wooden doors should have either a metal top rail to prevent centre flex or I have even seen people use a hardwood 2x3 screwed to the top.

    stand close to the door and operate the door and if you see any flex near the middle then YES get a top rail or devise one yourself. You may have to watch it a few times to be sure and also watch the wheel rails around the curve and see if they are tending to pull in a little.

    A possible temporary fix is to re-grease the curves with somthing suitable for your climate.

    If that helps at all then it is most certainly the flex that is causing the problem

    With belt units it is also possible that the belt has gotten a stretch point and there is a small amount of slack and some units can operate a little quicker on the uptake until the extra belt is taken out and this too can cause a **** but it is unusual to see that except on cheaper ones.

  • Project NOMAD
    Project NOMAD Aug 27, 2010

    oops forgot to mention why good mounting is important.

    If the drive can be pulled toward the door slightly then it has to work harder to start pulling up the door.

    That too can cause a flex on the door in a tug-o-war fashion the mountin will normally win but only after it has given way a little.

    Watch each part of the system to see where it moves and if the mounting moves fix that FIRST its also the cheapest fix to try as all you need is a couple of bolts and some more universal angle.

    If it is dropped from an extra high ceiling then add a rear diagonal from down near the drive at least 45 deg out to the back of the garage.

    Just did a twin garage with 12 foot ceilings and had to put twin diagonals on both drives or else the mountings would have just pulled thenselves to the door.

    I have presumed you checked the tracks and that they are running parralel and dont have any dings etc in them and they are mounted firmly



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