CONTROL GP-HYDRAULIC 1773567 - Caterpillar

Brake Unit (D40D Trailer Only)
Location of Trailer Brake UnitThe trailer braking units are oil immersed multiple disc type with pump circulated oil lubrication and cooling. For service and secondary brake operation the units are hydraulically applied with air/hydraulic actuator assistance. For parking the brakes are applied by power springs and released by hydraulic pressure.End plate (10) is bolted to axle casing (11). Outer casing (7) is bolted to the end plate. Stationary brake plates (13) are splined to the outer casing. Rotating brake plates (14) are splined to the final drive outer casing (15) and are free to rotate between the stationary plates and the final drive when the brake is released.Grooves in the plate faces allow circulation of cooling oil, whether the brake is applied or released.When the park brakes are disengaged, oil from the brake release pump is connected from the brake release pump through a port in the end plate to annular passage (2). The pressure of the oil offsets the park piston (5) to the right, compressing the power springs (12) until the piston contacts the housing at (9). This relieves the pressure from the brake pack and the plates are free to rotate.When the park brake is engaged, the oil flow from the brake release pump is cut off and the oil in annular passage (2) is connected to the brake oil tank through the brake release valve.As the oil pressure decreases, the park piston is offset to the left by the power springs until it contacts the service piston (3) and forces it into contact with the brake pack (1). This holds the rotating plates between the stationary plates and locks the final drive outer casing (15) to the axle casing (11).When the service brake is applied, oil from the trailer air/hydraulic actuator flows through a port in the end plate into annular passage (4). Oil pressure offsets the service piston to the left against the brake pack. Springs (6) are tensioned by pull rods (8) as the service piston moves.When the service brake is released, the air/hydraulic actuator draws oil out from annular passage (4). Springs (6) offset the service piston to the right, away from the brake pack. This relieves the pressure from the brake pack and rotating brake plates (14 ) are free to rotate with the final drive.
Trailer Brake Unit 1. Brake Pack2. Annular Passage3. Service Piston4. Annular Passage5. Park Piston6. Spring7. Outer Casing8. Pull Rod9. Housing 10. End Plate11. Axle Casing12. Power Spring13. Stationary Brake Plate14. Rotating Brake Plate15. Final Drive Outer CasingPark Brake Release Valve (D40D)
The park brake release valve is located at the bottom of the hydraulic module on the rear of the tractor.
Location of Park Brake Release ValveWhen the park brakes are engaged, spool (6) is fully offset by return spring (11). Pump oil entering the valve at inlet port (1) flows past check valve (9) and is blocked by the spool (6). When the pressure of the oil reaches the setting of relief