SPRING 0549006 - Caterpillar

The towing brake release system must only be activated by a towing hook securely attached to the recovery machine. The towing hook must be securely attached to the towing hitch of the disabled machine prior to activating the release system. Failure to do so may result in the disabled machine moving, causing serious personal injury or death.When the disabled machine has been towed to a safe place, ensure it is parked on a level surface and the wheels are blocked securely so that the machine can not move prior to any service work being performed on the machine.Ensure the disabled machine can not move before disconnecting the towing hook.
If the parking brake is engaged due to a machine fault and the machine must be towed, the towing brake release system can be used to release the machine brakes.The towing brake release system can be activated by a towing hook compressing the piston in the towing brake release cylinder. The towing brake release cylinder is located in the machine towing hitch at the rear of the machine.The towing brake release system consists of the following components: towing brake release cylinder (10), check valve (11), towing brake release sequence valve (12) and shuttle valve (18).
Rear of the machine(10) Towing brake release cylinder.When the towing brake release system is activated, the piston in towing brake release cylinder (10) is forced upwards against a spring in the cylinder.
Left Side of the Torque Converter Compartment(11) Check valve (obscured).(12) Towing brake release sequence valve.
Left Side of the Transmission Compartment(18) Shuttle valve.The hydraulic oil in the towing brake release cylinder is forced from the cylinder and directed through shuttle valve (18) to the wheel brakes. The oil pressure then releases the parking brake section of the wheel brakes.When the towing brake release system is deactivated, the force on the piston in towing brake release cylinder (10) is removed. The spring in the towing brake release cylinder causes the piston to move downwards. The pressure of the hydraulic oil in the parking brake section of the wheel brakes is released and the oil flows back to towing brake release cylinder (10). The parking brake will now be engaged by the springs in the wheel brakes.Towing brake release sequence valve (12) ensures that when the parking brake is disengaged during normal machine operation, the towing brake release system is disabled.Recovery Hook
Hydraulic Schematic for the Braking System(1) Rear brake accumulator.(2) Front brake accumulator.(3) Service brake and transmission neutralizer pedal.(4) Service brake pedal.(5) Service brake control valve.(6) Rear wheel brakes.(7) Brake accumulator charging valve.(8) Service brake low oil pressure switch - alert indicator.(9) Service brake low oil pressure switch - brake activation.(10) Towing brake release cylinder.(11) Check valve.(12) Towing brake release sequence valve.(13) Manifold.(14) Front wheel brakes.(15) Parking brake control valve.(16) Parking brake oil pressure switch - alert indicator.(17) Parking brake oil pressure switch - remotes light.(18) Shuttle valve.(19) Check valve.(20) Brake and pilot pump.(21) Pilot oil pressure reducing valve.(22) Hydraulic tank.(23) Vacuum breaker/relief valve.(24) Recovery hook.(AA) Pressure test