said by Kugar13 :I would assume the gear wheel sheered, as my research indicates this is a regular problem with garage door openers, but that wouldn't explain why the garage door opener lurches forward/backward a foot before failure once the door is re-attached to the garage door opener/chain.
When you re-attach the chain, you hit a spot in the gears where they mesh ok, so it moves a bit, but then gets to the bad spot and never re-engages. I'm in agreement that a gear is hosed.
TD