On Sun, 15 Nov 2015 14:22:10 -0500, wrote:

On Sun, 15 Nov 2015 14:12:23 -0500, Micky
wrote:

On Sun, 15 Nov 2015 17:39:47 +0000 (UTC), "badgolferman"
wrote:

badgolferman wrote:

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?

Here are some pictures:

Internal gear
https://drive.google.com/file/d/0B4R...d2ZlpvZEk/view

Belt
https://drive.google.com/file/d/0B4R...JfcmVqeEk/view

Looks like the gear is stripped and the belt is bad. How can I
diagnose the motor?

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.
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.