Worm reducer and method for manufacturing worm reducer

A method for manufacturing a worm reducer including a worm shaft, a worm wheel, a housing that houses the worm shaft and the worm wheel, a bearing that holds the worm shaft inside the housing, a coil spring that contacts an outer peripheral surface of the bearing and applies an urging force toward the worm wheel, and a preload member that is screwed into and fixed to the housing and pressurizes the coil spring, the method comprising:

• disposing the coil spring such that one end of the coil spring in a winding axis direction contacts the bearing;
• and
• screwing the preload member into the housing,
• wherein a winding direction of the coil spring is different from a winding direction of a thread of the preload member, and contact resistance between the coil spring and the preload member is greater than contact resistance between the coil spring and the bearing,
• wherein in an initial stage in which the preload member is screwed into the housing, the coil spring is rotated together with the preload member, and
• wherein in a final stage in which the preload member is screwed into the housing, a position of a first distal end portion of a wire rod forming the coil spring is disposed within a predetermined circumferential range around a winding axis of the coil spring, so that the first distal end portion is located on a side of the bearing, and the preload member and the coil spring slide along with each other towards the bearing, thereby the preload member is attached to the housing.