Rail car brake system

In a rail car truck having a support member and rail wheels, a brake mechanism for each wheel comprising a brake head and shoe carried thereby, hanger means pivotally suspending said brake head from said support member, a long-lead screw, a nut carried by said brake head and receiving one end of said screw, a housing mounted on said support member, anti-friction bearing means in said housing and rotatably supporting the other end of said screw, a pneumatic cylinder and push rod operative thereby and means connecting said push rod with the outer end of said screw whereby admission of compressed air into said cylinder will rotate said screw and advance said brake head and shoe essentially linearly towards and into braking engagement with a wheel, said bearing and hanger means acting to minimize frictional resistance to the linear motion of said brake head while maintaining said brake head positively in proper angular relationship with said wheel, said bearing means including a diametrically split spherical bearing providing opposed spaced planar faces, one of which split bearing portions is mounted for rotation with said screw and the other of which floats thereon, a pair of rings in said housing providing an outer race for each of said split bearing portions respectively, and an anti-friction, free-floating roller bearing positioned on said screw between said faces and bearing thereon to combine with said floating split bearing portion and absorb reactive thrust when the brake is applied while said spherical bearing carries the radial loads.