BEARING 4789271 - Caterpillar

Illustration 1 g00763490
View from the Right Rear of the Tractor (1) Tractor brake actuator
Illustration 2 g00763491
View Under the Rear of the Scraper (2) Scraper brake actuator
Illustration 3 g00763495
Brake Actuator (3) Parking and secondary brake chamber (4) Parking and secondary brake springs (5) Parking and secondary brake piston (6) Service brake chamber (7) Service brake diaphragm (8) Rod (9) Service brake return springTractor brake actuator (1) is located to the inside of the tractor wheels. Scraper brake actuator (2) is located to the inside of the scraper wheels.Each brake actuator has two air chambers, which are the parking and secondary brake chamber (3) and the service brake chamber (6). When there is no pressure in the air system, the air pressure in parking and secondary brake chamber (3) is released. Parking and secondary brake springs (4) move parking and secondary brake piston (5). This moves rod (8), which activates the brakes.The brakes stay activated until the air system is at the correct pressure for operation and the parking brake control is moved to the DISENGAGED position. The parking brake control valve is in the DISENGAGED position when the knob is pushed in. When the parking brake control is in the DISENGAGED position, the parking brake solenoid valve will open. Air pressure then goes into parking and secondary brake chamber (3). Parking and secondary brake piston (5) moves against parking and secondary springs (4). This moves rod (8) in order to release the brakes.When the brake pedal is pushed, air pressure from the brake control valve goes into service brake chamber (6). Service brake diaphragm (7) presses against spring (9), which extends rod (8) in order to activate the brakes. Air pressure in parking and secondary brake chamber (3) keeps springs (4) in compression.When air pressure decreases to approximately 379 kPa (55 psi), the parking brake solenoid valve closes automatically. This stops the flow of air to parking and secondary brake chamber (3), which removes springs (4) from compression. Therefore, springs (4) push rod (8), which activates the secondary brake system.The same operation takes place when the parking brake control valve is manually moved to the ENGAGED position.