Howdy all - very glad to find this great resource for help with my Craftsman garage door opener problems.

I'm working with a model 139.5361SR circa 1991 which is in very strong running shape and was working perfectly until it was removed to make way for a new door installation.

After reinstalling the unit and checking for clearances I attached the sled to the reinforced plate on the new door.

I noticed that the door would open to the correct height, but when closing it would go all the way down and then reverse itself (seemed to me that the lower limit was set "too long").

I attempted to adjust the limit screws on the side of the motor housing to reduce the downward travel but now the sled runs until its in a bind going up and/or down. I've returned the limit screws to their original positions but still the sled (with, or without the door attached) runs until it's hitting the wall, or until it binds up on the track bolt near the motor. I actually had to loosen the chain and take it off of the gear on top of the unit to get it to unbind when in the "up" position.

Can someone better explain to me how the upper and lower limits are determined by the unit (in number of revolutions, or running time, or ???), or suggest a way to "zero" things out to a sane adjustment that I can then work from to get everything just right? Any way to tell if my adjustments are just very out-of-whack, or if I may have fried the logic board by putting it in such a bad bind?

Thanks in advance for reading, and for any further suggestions, questions, etc!