Air-Hydraulic Brakes Of Large Trucks

The Brake System:

Air-Hydraulic Brakes Of Large Trucks

The principles of operation of the air-hydraulic brakes of the 5-ton, 6x6 trucks can be applied to the air-hydraulic brakes of the 2 1/2-ton-series trucks. However, there is enough difference in the design of the two brake systems so that a short discussion on the 2 1/2-ton truck brakes is needed.

The air-hydraulic cylinder of a 2 1/2-ton truck looks different from that of a 5-ton truck, but the operation is about the same. Brake fluid applied pressure from the master cylinder is transmitted to the slave cylinder and the fluid passage at one end of the hydraulic control valve piston. The control valve piston then pushes on the slave cylinder compensator piston moving it to close the air exhaust valve and open the air inlet valve. Air pressure from the reservoir flows through the air inlet opening and out one control line to the power cylinder and a second control line to the trailer service coupling.

Air pressure on the compensator piston and hydraulic pressure on the control valve piston oppose each other to regulate the controlled air pressure. When the brake pedal is released, hydraulic pressure is removed from the control valve piston and the compensator piston spring returns the compensator piston and control valve to the released position. This allows the air inlet valve to close and opens the air exhaust valve. Controlled pressure is exhausted through the hollow compensator piston and out the air breather port.

The power cylinder and hydraulic slave cylinder work just like the power and slave cylinders on the 5-ton truck with two exceptions. The hydraulic piston is returned by inner and outer slave cylinder piston springs. There is no residual line pressure check valve in the outlet of the 2 1/2-ton truck's slave cylinder like on the 5-ton truck. The 2 1/2-ton M35-series truck has the residual line pressure check valve in the outlet of the master cylinder.

The M35-series cargo trucks do not have a hand control valve or trailer couplings at the front of the truck as the 5-ton truck does. However, they do have service and emergency trailer couplings at the rear of the truck. The 2 1/2-ton tractor trucks have a hand control valve so the trailer brakes can be operated separately.

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Article Pages
1. The Brake System
2. Introduction
3. Principles Of Braking
4. Braking Requirements
5. Factors Controlling Retardation
6. External-Contracting And Internal-Expanding Brakes
7. Brake Types
8. Brake Drum Construction
9. Brake Shoes
10. Rotating And Non-Rotating Units
11. Self-Energizing Action
12. Disc Brake
13. Comparing Disc And Drum Brakes
14. Floating Caliper
15. Fixed Caliper
16. Hydraulic Brakes
17. Master Cylinder
18. Wheel Cylinder
19. Hydraulic Brake System Insepction
20. Before Road Test Inspection
21. Road Test Inspection
22. After Road Test Inspection
23. Air-Hydraulic Brake System
24. Air-Hydraulic Master Cylinder
25. Air-Hydraulic Cylinder
26. Air Compressor
27. Air Governor
28. Air-Hydraulic Brake System Components
29. Trailer Coupling Hoses And Connectors
30. Air-Over Hydraulic Cylinder
31. Operation Of Air-Hydraulic Brakes
32. Air-Hydraulic Brakes Of Large Trucks
33. Trailer Air-Over-Hydraulic Brake Systems
34. Air-Hydraulic Brake System Inspection
35. Before Road Test Inspection
36. Air-Hydraulic Brake System Road Inspection
37. Trouble Shooting Air-Hydraulic Brakes
38. Air-Brake System
39. Air-Brake Quick Release Valve
40. Air-Brake Relay Valve
41. Air-Brake Chamber
42. Air-Brake Slack Adjuster
43. Air-Brake Auxiliary Components
44. Semi-Trailer Air Brake Systems
45. Operation Of Straight Air-Brake System
46. Miscellaneous Air-Brake Components
47. Troubleshooting Straight Air Brake Systems

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