sound as a bell
In excellent condition, as in Now that the brakes have been relined, the car is sound as a bell, or The surgery went well and now he's sound as a bell. This simile rests on the assumption that the bell in question is not cracked (which would make it useless). First recorded in 1565, it has survived numerous other similes (sound as a top or roach or dollar), probably owing to its pun on "sound."