Abstract: A proportioning relay valve (10) includes a housing (12) receiving a relay piston (28) which controls communication between supply (14), exhaust (18) and delivery or outlet (16) ports. Control pressure is communicated to the relay piston (28) through a proportioning piston (58). The proportioning piston (58) is controlled by the pressure level at the actuating pressure port (22) to proportion communication to the relay piston (28) when the pressure level at actuating pressure port (22) is low and to permit unproportioned communication to the relay piston (28) when the pressure at actuating pressure port (22) is high. A bypass passage (80) and relief valve (86) also control the proportioning piston (58) so that unproportioned communication to relay piston (28) is permitted regardless of the pressure level at the actuating pressure port (22) when pressure at the control port (20) exceeds a predetermined value.

Abstract: A dual circuit brake valve for an articulated vehicle is responsive to a pressure signal provided by the system tractor protection valve to provide a full brake application in both the primary and secondary braking circuits actuating the front and rear wheel brakes of the vehicle respectively when the portions of the articulated vehicle are connected for movement together. A proportioning piston is responsive to the pressure signal to proportion braking pressure in the secondary when the towing portion of the vehicle is operated in the "bobtail" mode without the towed portion of the vehicle. The brake valve includes mechanism for mechanically actuating the secondary circuit valve to provide a full brake application under emergency conditions during operation of the vehicle in the bobtail mode.

Abstract: A clutch drive (10) includes a spindle (16) mounting a driving member (94) and a driven member (118) for rotation about the spindle (16). The driving member (94) includes a pressure plate (96) which moves axially along the spindle to engage and disengage from the driven member (118). The pressure plate (96) is mounted on circumferentially spaced pins (102) which are slidably received in apertures (106) in the pressure plate (96). Circumferentially spaced springs (112) yieldably urge the pressure plate (96) into driving engagement with the driven member (118). A fluid pressure responsive piston (52) is connected to the pressure plate (96) by a bearing (68) and urges the pressure plate (96) away from the driven member (118).