question on garage door opener

I have a Genie screw drive at a house with a double garage. The door is just a single big piece (not sectional), about 7' tall x 16'wide. When the opener closes the door and it's all the way down, then naturally the opener shuts off. But now the door has started coming back open 6 inches or so and the screw drive turns backwards. I don't think it used to do this and I thought that simply because of how screw systems work it should be almost impossible to make the screw turn backwards. You can pull up on the door and open it further (screw drive turns backwards and lets it open).
???????
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Ashton Crusher wrote:

Hi, I have same opener, Genie screw drive on a same size sectional door. There is two adjustment, limit switches(one for up, one for down) and clutch. Check the manual.
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responding to http://www.homeownershub.com/maintenance/question-on-garage-door-opener-704622-.htm DA wrote: Ashton Crusher wrote:
You can pull up on the door and open it further

These garage door screws look like two-start, 1/8" pitch and so to pull on the nut and make the motor shaft turn as a result, you would have to exert an enormous lateral force. It will most likely result in you stripping the nut's thread (or teeth - this isn't a "normal" nut, it's a part of the carriage, the part with the emergency release cord)
I think the only way you could manually make the door move when the screw is still engaged and observe the screw rotate is when the motor wants to rotate the screw in this direction anyway but does not have enough power to lift the door by itself. By manually lifting the door you essentially just help the motor rotate the screw. In other words, it's not you rotating it, you just happen to help it along.
The motor's force is adjustable - either electronically with two potentiometers on newer openers or with a clutch on older ones. It's possible that if you adjust the opening force higher, the door would back out all the way. Are the door and the screw lubricated? Does it open easily enough when the screw drive is disengaged?
Anyway, your Genie (which model is it, BTW?) should have safety features that make it open if the closing limit switch has not been tripped in 30 seconds or if the power draw of the motor suddenly increased indicating that the door hit something on the way down. If you did not touch the door at all after it backed out 6", what would happen? Will it just continue to sit like that?
If the door itself is mechanically sound, lubricated and balanced, I believe there is something with the closing limit switch - it's either out of proper position or damaged (corrosion of mechanical damage) and no longer shorts the contacts when pressed. Move it closer toward the motor and see if the door stops reversing (even if this makes it not to close completely). If there's no change in the behavior, verify the wiring of the switch and if it's fine, change the switch. If that does not help, there can always be a problem with the control board.
------------------------------------- /\_/\ ((@v@)) NIGHT ():::() OWL VV-VV
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On Sun, 15 Jul 2012 01:13:11 +0000, DA

Everything you say is correct as I understand things. That's what's so odd. You can pull up on the door and it makes the screw rotate backwards and the door can be opened. I thought that by the nature of this type of screw mechanism it should be impossible to do that. The motor is not running, just turning backwards. The "jaws" that run along the screw are not stripped.
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On Saturday, July 14, 2012 3:46:37 PM UTC-7, Ashton Crusher wrote:

First check the clutch to see if it's tight. If it's not tight then try tightening it. If it doesn't tighten then read the following:
The Genie SD9500 may not have a washer on the drive screw between the drive screw tuggnut retaining clip and the end of the track. The end of the track is uneven and will break the tuggnut retaining clip if it makes contact with it causing the clutch plates to permanently separate or disengage, preventing the motor from turning the drive screw. A section of the track is attached to the motor head by two bolts and bolt inserts and is not designed to be removed. After removing the bolts the inserts will have to be punched out in order to gain access to where the tuggnut retaining clip is in order to install a washer there; however at least you will not have to re-install the inserts but can use bolts with a larger diameter instead.
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On Sat, 14 Jul 2012 18:19:13 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

screw tuggnut retaining clip and the end of the track. The end of the track is uneven and will break the tuggnut retaining clip if it makes contact with it causing the clutch plates to permanently separate or disengage, preventing the motor from turning the drive screw. A section of the track is attached to the motor head by two bolts and bolt inserts and is not designed to be removed. After removing the bolts the inserts will have to be punched out in order to gain access to where the tuggnut retaining clip is in order to install a washer there; however at least you will not have to re-install the inserts but can use bolts with a larger diameter instead.
Maybe the "washer" or something is just worn out. The opener is around 34 years old and it's never been taken apart so nothing should be out of place. It used to work fine but now it's got me stumped. I don't think it's a clutch adjustment because it takes a lot of power to pull this door and it's not slipping when it's opening or closing it.
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