Garage door closes, then automatically opens halfway

[soonerbrink]

I have a liftmaster 3245 garage door opener.

The garage door closes the automatically opens and stops halfway

First I tried adjusting the force adjusting the force an height of the door, but this did no affect anything.

I disconnected the door and the opener still functioned the same without the door connected.

The track appears to be clean and I don't see anything different on the portion where it stops.

Any suggestions on how to fix?

[TJR]

The bushings at the drive sprocket and at the limit assembly are worn out. It skip the gear in the limit assembly and the open/close limit will be off.
Did you tighten the chain lately?
To fix your problem you will need a gear/sprocket rebuild kit, you can get it HERE

[soonerbrink]

The bushings at the drive sprocket and at the limit assembly are worn out. It skip the gear in the limit assembly and the open/close limit will be off.
Did you tighten the chain lately?
To fix your problem you will need a gear/sprocket rebuild kit, you can get it

Thank you for the reply!

The chain is very loose and hangs down several inches below the track all the time. I tightened it up and it was quieter and did not rub against the top of the door. I wasn't sure how much to tighten it, but I found in the manual where it should be 1/2" above the rail when open, and it looks like the is a little piece for it to rest on, located on the part that catches the door.

Is it possible for me to visibly verify this is the problem by opening the unit? I have trouble understanding how it opens fine until that point, because the gear/sprocket will have rotated numerous times and resistance is not increased because the door is off. Or perhaps it's just the fact that the part is worn out, so it doesn't know when to stop and it just happens to be that location.

Also my unit doesn't have a sprocket cover as shown the manual. I assume I should purchase one of these as well?


Thanks again!

[TJR]

Just look on top of the opener at the drive sprocket and you will see some black powder like stuff and maybe some pieces of the bushing. When you open the box(DISCONNECT THE POWER FIRST) the big white gear will be full of the same black stuff and you will have it in the cover too.
When you tighten the chain you put more pressure on the worn out bushings and make the limit gear skip.
When you closing it will over run and hit the pulley bracket and reverse, then stop half way open. The open/close limit is out of adjustment because the limit gear skipped.

[soonerbrink]

Just look on top of the opener at the drive sprocket and you will see some black powder like stuff and maybe some pieces of the bushing. When you open the box(DISCONNECT THE POWER FIRST) the big white gear will be full of the same black stuff and you will have it in the cover too.
When you tighten the chain you put more pressure on the worn out bushings and make the limit gear skip.
When you closing it will over run and hit the pulley bracket and reverse, then stop half way open. The open/close limit is out of adjustment because the limit gear skipped.

Sounds exactly like the symptoms I have. When I was looking at it last night I noticed a lot of the black powder and small pieces on top.

I am am also concerned about tightening the chain too tight now. From the instructions it sounds like slack is okay when it is open. When the door is closed should the chain hang below the guide?

Thanks again!

[TJR]

You did tighten the chain correct, but with worn/damage parts and that don't make anything better and absolute not fixing the problem. When you connect the door(putting load on the opener) yes the chain can drop onto the rail or little below.
You might like to check the balance on the door, stay by it self about half way point and full open with risk of dropping. Also make sure it's not sticking or binding. Lube all the hinges, roller shafts, moving points and parts. The easier and smoother the door open/close, the less wear and tear on your opener.

[soonerbrink]

You did tighten the chain correct, but with worn/damage parts and that don't make anything better and absolute not fixing the problem. When you connect the door(putting load on the opener) yes the chain can drop onto the rail or little below.
You might like to check the balance on the door, stay by it self about half way point and full open with risk of dropping. Also make sure it's not sticking or binding. Lube all the hinges, roller shafts, moving points and parts. The easier and smoother the door open/close, the less wear and tear on your opener.

What do I use to lube the door?

...the spring?

...the chain?

I opened the unit and snapped some pics (Top of main gear with residue, view of more componets, exterior of unit)

[TJR]

Pretty much any spray lube will do. The only one I don't recommend are the lithium spray lube. You can also use 3in1 oil, with a couple drops on each joint and roller shaft. Do not grease the tracks for the door and try to spray away from the track if you use a spray lube. Give the spring/s a light spray and the same for the cable drums.
LiftMaster do not say anywhere in their manual about lube the chain, but if you do spray it with some lube I don't think you do any harm. They do recommend every 5 years or so to clean the rail for old grease and apply a thin layer of lithium grease (get the lithium grease in a tube) both on the bottom and the on top of the rail where the trolley glides.

[soonerbrink]

Thanks again for all the help. I visually saw how the limits work when I took apart the housing of the unit. Somehow they were way off, and I had to dial back the middle screw so the limits would be within the acceptable range. There wasn't any extra room for the high limit to move up. I don't know if something else was causing it to be way off, but it works fine for now and will go back to troubleshooting if it acts up again.

[TJR]

If you didn't replace the gear/sprocket assembly, it will act up again and you can keep reset the open/close limit till the sprocket pop off.

[HomeI]

depending on the brand and make, you may need to replace the cpu chip.

[rapghsi]

finally find this thanksss