Pull out all the stops

A rare case of an idiom with a completely literal, mechanical origin. On a pipe organ, "stops" are knobs that control which ranks of pipes are allowed to sound: pushed in, they silence a set of pipes, and pulled out, they let them play. Pulling out every stop unleashes the organ's full volume and every tonal colour it has. The metaphorical use for giving something everything you've got dates to the mid-1800s.