Rear view of wheel brake assembly
(1) Purge port and test port for the service brake and retarder
(2) Purge port for the parking brake
(3) Brake wear indicator port
(4) Outlet passage for the brake cooling oil
(5) Oil passage for the service brake and retarder
(6) Inlet passage for the brake oil cooling
(7) Oil passage for the parking brake
Components of a wheel brake assembly
(8) Brake housing
(12) Oil chamber
(15) Duo-Cone seal
(16) Wheel assembly
(19) Duo-Cone seal
(20) Piston housing
(21) Oil chamber
(23) Brake housing
The service and parking brakes are located between the axle housing and the final drive.
The service and parking brakes are an oil immersed, multiple disc type brake group. Each brake group consists of a service brake piston and a parking brake piston. The service brakes are applied by hydraulic oil pressure and disengaged by springs. The parking brakes are engaged by springs and disengaged by hydraulic oil pressure.
Wheel assembly (16) is connected to brake housing (8) by spindle (25) and two taper roller bearings. Brake housing (8) and spindle (25) do not turn. Piston housing (20) , brake housing (23) and plate (24) are bolted to brake housing (8) . Plates (13) are splined to brake housing (23) . Plates (13) do not turn. Discs (14) are splined to wheel assembly (16) . Discs (14) turn with wheel assembly (16) .
Brake cooling oil flows into the wheel brake through passage (6) . The brake cooling oil cools the discs and plates. The brake cooling oil then flows out through outlet passage (4) . The brake cooling oil returns to the hydraulic tank.
Purge port (2) is used to remove the air from the hydraulic system for the parking brake. Purge port (1) is used to remove the air from the hydraulic system for the service brakes and retarder.
Parking Brake Application
The parking brakes are applied by springs and released by oil pressure. When the parking brakes are engaged, springs (17) and (18) push on piston (11) . Piston (11) pushes discs (14) and plates (13) together and friction occurs. The friction prevents the wheel assembly from rotating.
When the parking brake is disengaged, pump pressure is sent to oil passage (7) . Oil then flows into oil chamber (12) . The oil pressure forces piston (11) to compress springs (17) and (18) . Piston (11) moves away from discs (14) and plates (13) . The discs and plates will not be in contact and the parking brakes will be disengaged.
Service Brake Application
When the service brakes or the retarder is applied, oil pressure flows to oil passage (5) . Oil then flows into oil chamber (21) . As the oil pressure increases, piston (22) pushes discs (14) and plates (13) together and friction occurs. The friction causes the rotation of wheel assembly (16) to slow. A continued application of the service brake or retarder stops the rotation of wheel assembly (16) .
When the service brakes are released, springs (9) and spring guides (10) pull piston (22) away from discs (14) and plates (13) . The discs and the plates will not be in contact and the service brakes will be released.