It sounds like you left the revolution counter cup (black plastic w/
notches in the side) off or it isn't seated properly on the end of the
motor shaft. This is part of the reversing system & is like a timing
circuit. The board on the end of the motor sends pulses thru the
notches & when the timing of the pulses change (motor slows down) the
door reverses. When this part isn't working properly the door will
move exactly 4" in either direction.

DoorDoc
www.DoorsAndOpeners.com
www.ActionDoor.com

On Jan 28, 7:14 pm, wrote:
Hi,
This is about a Craftsman chain drivegaragedooropenermade in 1996.
It stopped working a few days ago, and after disassembling it, it was
obvious that the gear and sprocket needed to be replaced. I did
replace those parts, but after putting everything back under the
ceiling again, thedoorwon't move much anymore.
The chain moves a few inches in one direction, then reverses, moves a
few inches in the other direction and then stops. This occurs
independent of whether thedooris locked into the chain, or whether
the chain moves without thedoor.
Of course, I had to loosen the chain during the installation, so does
this sound like I tightened it too much (or not enough?) when
reinstalling it?
Or could this be a safety "auto reverse" issue? But would that also
explain what happens when thedooris disconnected? Are the three
wires that go into in the back of the unit part of the auto reverse
process?
Most importantly, I would of course like to find out how to solve the
problem, so any suggestion would very much be appreciated.
Thanks,
Tim.