Liftmaster Formula I.
When I hit the button the motor makes noise but the belt doesn't move. The door moves on the track freely when I lift it manually. Examining the belt I see the rubber has separated near the motor and only the steel belts are visible. There is maybe an inch or two of slack in the belt when I pull on it. This belt seems to be the problem to my untrained eye. Is this something I can fix on my own?
Are you just saying you have a bad belt? With the door disconnected from the trolley, can you move the driven pulley? (making the trolley move)
Sounds like belt is a toast. How about replacing the belt? If you don't try you'll never learn. There is many Youtube how to do out there. My GDO is screw drive type, no belt to replace or wear out!
No, I can't move the belt by hand. Should I be able to? It's still attached to the motor and gear at the other end.
I don't want to replace the belt and find out the motor is bad. I'm trying to diagnose the problem with your help.
Look at the trolley and be sure it is not jammed into the back end. You can take the belt off to break the tie but if it is loose you should be able to see if it is the motor or the driven pulley that is locked up. My bet is the trolley missed the stop switch and crashed into the bumper so hard it jammed. Sometime you can rock the door while someone hits "go down" and break it loose.
Here are some pictures:
Internal gear
Belt
Looks like the gear is stripped and the belt is bad. How can I diagnose the motor?
Release the door from the opener. Engage the door with the opener while you are viewing the motor and gears. Do they turn? Yes, replace gear and belt. No? Motor is shot. Buy a new GDO.
The gear does look pretty rough but it is just worn, not broken. Start be seeing of there is any "wink" in either belt pulley. One should move until the belt stops it. the other may not move at all. If the motor seems to be moving, look towards the chain end. Work your way through it until you see what is stuck. Taking the belt off may be the way to start but since you want to replace the pulley anyway, going at it from that end may be better. That doesn't look like the 3 GDOs I have here to look at so I will be short on details about how the drive works.
I imagine there is a you tube these days telling you how to go at taking this apart.
You could look at it this way: The motor must have been pretty strong to strip the gear like that, and once the gear is stripped, the load on the motor is (much?) less so there's not much reason for it to wear out after the gear is stripped.
If the gear that engages the belt is on the part of the belt with no teeth, that presents almost no load for the motor.
That gear is certainly worn, probably running for years without any grease but it isn't stripped. Something bound up and it might be as simple as the trolley jammed into the stop. That is fairly common with Chamberlain/Craftsman. It is pretty high on the trouble shooting chart in the owner book.
If the motor runs and the door doesn't move, and the belt is chewed up - I'd spend the couple bucks for a new belt and give it a try. About 95% chance everything else is OK. The remaining 5% is the chance something else is badly warn and jammed the thing up, causing the belt to go.
It is VERY obvous you fall into the 5% - the gear is stripped and the belt is totalled. You need a complete rebuild kit (full set of gears and belt) By attempting to run the door up or down the motor will be run. If you hear it spin it is OK. You will want to be a pretty reasonable handi-man to do the rebuild yourself. You will need a few tools. You might want to ask for some help from a friend who is more mechanically inclined than yourself as, although it's not "rocket science" it is a bit more involved than changing a light bulb.
Just look at the posted pictures. VERY obvious the gears and belt are both "toast"
The "timing belt drive" transmits power from the motor to the worm gear, which then turns the pinion that drives the chain to move the door. The pinion is so badly worn the worm has "climbed the teeth" jamming it up, causing te motor to take the teeth right off the belt, right down to the cords. No idea how old the GDO is - or what brand - looks like an old Chamberlain Liftmaster of some type - likey 30 or more years old? Parts will still be available but owner will need to decide weather to spend $30 on a gear kit
I've rebuilt a few of them over the years
That gear IS totally worn out. Replacing the belt without replacing the gear guarantees the new belt will not last. The worm gear has "climbed" the pinion and jammed solid - causing the motor to take the teeth off the belt. I've done several of these units - with the same problem. Sometimes the gear will torally strip without taking the belt out - but when the belt is gone like that, and the obvious signs of gear failure are so evident - it is almoast a dead giveaway that the gear has jammed due to excessive wear.
Okay, I took the belt off and the plastic gear assembly. The motor drives just fine and the worm gear seems to be fine too. The gear was totally dry with no grease on it.
I ordered the replacement parts for my Liftmaster 1280R. Hopefully this works.
Gear and internal guts $13.90:
We don't know your skills, but some home owners can.
I'd be tempted to remove the cover, loosen the adjuster, remove the belt. Then try the opener and see if the motor spins.
New belts should not be all that expensive. Tighten, and recheck and retighten in about a week, they loosen up.
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He still seeks clarification of a working motor and has stated he doesn't want to replace the belt and gear to discover the motor is fried. Allowing the motor to run without tension will confirm his concern.
The couple of GDO I've serviced, I can usually move the belt by hand, even when attached.
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