I replaced the plastic gear in my Liftmaster garage door opener. the motor activates. it lifts the door up an inch then puts it right back down. Tension and travel settings don't help

Chances are you have a broken door spring or a bad drive gear in the opener. Remove the cover from the motor unit to check the gear. It will be obvious if it is bad.

Hello,

The problem is not the chain, it is the plastic gear in the unit of the liftmaster Garage Door 1/2 Hp.The plastic gear is not engaging, although it sounds like it is working.

You will have to replace it with a new one, then the liftmaster Garage Door 1/2 Hp will be able to open up once again.

Once you open and remove the old gear, Be sure to thread the screws in all the parts before you install them. Pre-threading them once would really help. Secondly, label the wires on the back of the opener before lowering it to the ladder, so you can put them back in their proper place.

Hope this was helpful.
Goodluck
Elect_Comp

Check your door springs and also remove the cover from the motor unit and check the drive gear. It is a white nylon gear just in front of the motor and may be stripped.

It sounds like you have a broken door spring or the drive gear in the opener is stripped. You will have to take the cover off the opener and you will find the white nylon gear just in front of the motor.

Okay here we go.

Make sure you put the black cup back on the end of the motor shaft and that it is pressed all the way on. Make sure the RPM sensor is plugged in. If neither of these is the issue, then you probably did not have the motor shaft pushed all the way back when you tightened the coupler after replacing the worm gear. Loosen that coupler up and from the front of the motor (opposite end in which the coupler is on) push the shaft back as far as it will go. Hold it there while you tighten the coupler back up and then give it a try.

you need to replace gear when the door is fully closed. then do your tweaking.

You need to adjust the limit settings. There are two white screws on the side of the opener. One adjusts the down limit and the other adjusts the up limit. One full turn adjusts the door approx two inches, so turn the screws in small increments and see how much more to adjust.

I had the same problem. Took the cover off of the opener and found that the gears were stripped on the unit. Motor was fine. You can order gear replacement kit for the unit. They are a plastic type sprocket and worm gears. The kit comes with spindles and all necessary clips. You have to take the unit off the ceiling to replace the gears, but the process if very easy to do. Parts kit about $40 on line, much cheaper than a new door opener. Total process took less than 2 hours, including getting the unit down and back up again.

I managed to troubleshoot this myself and got my door working. The problem was that the black rpm wheel was not far enough down on the gear shaft. By unscrewing the screws on the final piece of the assembly on the shaft and then pushing it all more firmly toward the motor and rescrewing in place, I made it so the door operates beautifully.

I am sure that your lift gears have stripped and need to be replaced.