To simplify a housing manufacturing process having a through-opening, such as an oil release hole, formed in a housing outer wall and to reduce a manufacturing cost by a method wherein at least one of a plurality of longitudinal splines formed in the inner surface of the outer wall of the clutch housing of a transmission for vehicle is more deepened than other splines, and cross a peripheral groove formed in the outer wall of the housing.

In this clutch housing 10, a longitudinal spline 22 is formed in the inner surface 18 of the outer wall 16 of the clutch housing 10. Some of splines 22 are deeper in depth than the other. A peripheral groove 24 is formed in the outer wall 20 of the clutch housing 10, and crosses the spline having deeper depth, and this way forms a through-opening 26. This through- opening 26 is used as an oil release hole or a speed sensing slot.