My guess is that it's traveling towards the door because its internal mechanism is in the 'door is open' position. When you reconnected the door and trolley, after replacing the gear/shaft assembly, did you do so with the door, trolley and chain in the same position as before you took it apart and did you operate it once, unconnected to the chain?
I'd operate the GDO once, unconnected to the chain to reset its internal mechanism to the 'door closed' condition, reattach the chain, and cycle it again.
BTW, do not use pliers to wrench the chain off of the sprocket, especially while it's running. Disconnect the chain at the trolley to remove it.

Thanks for your speedy reply!

I'm fairly certain the chain and trolley were in different positions when I tried to re-attach. The door was the same - closed. :)

The first time I ran the motor after replacing the internal parts, I did have the chain on it, but not attached the door. After that didn't work, I disconnected the chain from the sprocket.
I then tried cycling the motor with the chain off (it went clockwise for 5 seconds, then immediately counter-clockwise for 5 seconds - I didn't think that would be long enough for a full cycle). That's when I reconnected the chain, and experienced the 'jamming' closed when trying to run it again.

Thank you for the tip on disconnecting the chain at the trolley - that sounds much easier!

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 are 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 try it.

Thanks, don. I'll try those steps next and will report back.

don - You were spot on!

I was a little frustrated to have to take the motor down again to re-do the assembly, but that was just the ticket. I put it back up after doing so, and when I pushed the button it moved back and forth between the up and down contacts like a charm!

I did have to adjust the up and down contact placement to fix the door travel, but got the hang of it quickly and now we're right as rain!

Thanks SO MUCH for helping this gal do it herself. It's a great sense of accomplishment.

A++++
Take care.

Kate

Kate thanks for letting us know it worked.