The invention concerns a window assembly in a vehicle having a window pane that is fixed in a window frame that is also used for movable windows, and a method for mounting the fixed window pane in the window assembly. The method may include: mounting a window mounting assembly to a vehicle structure adjacent to the window opening; sliding the window pane into run channels of the vehicle window frame; mounting a lower edge of the window pane onto a peripheral support surface of a window support cam of the window mounting assembly; rotating a cam lobe of the window support cam into contact with the lower edge of the window pane until the window pane slides upward into a fully closed position; and locking the window support cam, against rotation allowing the window pane to lower, as the window pane is lifted into the fully closed position.