My garage door opens but does not close. I have a stanely screw drive model # sd550. I can get it to open but I can not get it to close. I am guessing my sensors are in the wrong place but I need a manual to help me figure out where to put them or someone who can help out

Sounds like the door sensors are misaligned or have quit working. Make sure they are pointed at one another and the small light on each one is lit and not flickering.

It sounds like it could be the start capacitor. This is the symptom when they go bad.

Release the door from the opener and operate it by hand. Make sure it is not binding at that point. It could just need a simple increase of the down force but it is unusual at that point of closing. Clean the track of any grease if there is a build up. The track should never be greased.

The shaft on these garage door motors are not direct drive systems. You'll have to open up the box to see what the actual problem is. I have had stuff like this happen where a gear just slipped out of place.

http://www.aaadooropeners.com/?gclid=CLH3wt628p8CFVZS2goduwSLYQ

Here is a link for a parts supplier. I don't know your model but it looks like most of the Liftmaster worm screw gears and drive gears are plastic so it's possible that one of them has cracked.

The down limit switch could be set to low. Try moving the screw clockwise to raise the stop point.

Unplug the unit and remove the cover, usually eight screws, if you see a lot of white dust in the cover check the nylon drive/worm gear, they will need to be replaced.

If the door runs fine then check the up force and down force on your operator (the box that hangs from the ceiling). If the light(s) on your operator go from front and/or back, the force adjustment screw is on the back of the operator. If the lights are on the sides of the operator then the force adjustment screw is on the right side (looking from the back of the operator and facing the garage door). Turn the light blue adjustment screw with the up/down arrow to a higher number.

springs are shot/wrong. door not balalnced.

If you have a keyless entry it will still open the door with the vacation lock on. I assume you tryed this or don't have a keyless entry. There is no other way to activate the operator. Sorry but you will have to make a way in.

read manual, if you have, on trolley engagement