External-Contracting And Internal-Expanding Brakes

The Brake System:

External-Contracting & Internal-Expanding Brakes

Principles of External-Contracting & Internal-Expanding Brakes

There are several types of braking systems. All systems require the use of a rotating (turning) unit and a nonrotating unit. Each of these units contains braking surfaces that, when rubbed together, give the braking action. The rotating unit on military wheeled vehicle brakes consists of a drum secured to the wheel. The nonrotating unit consists of brake shoes and the linkage needed to apply the shoes to the drum. Brakes are either the external-contracting or internal-expanding type, depending on how the nonrotating braking surface is forced against the rotating braking surface.

When a brake shoe or a brake band is applied against the outside of a rotating brake drum, the brake is known as an external-contracting brake. On this type of brake, the nonrotating braking surface must be forced inward against the drum to produce the friction necessary for braking. The brake band is tightened around the drum by moving the brake lever. Unless an elaborate cover is provided, the external-contracting brake is exposed to dirt, water, and other foreign matter which rapidly wears the lining and drum. This is particularly true with wheel brakes.

The nonrotating unit may be placed inside the rotating drum with the drum acting as a cover for the braking surfaces. This type of brake is known as an internal-expanding brake because the nonrotating braking surface is forced outward against the drum to produce braking action. This type of brake is used on the wheel brakes of cars and trucks because it permits a more compact and economical construction. The brake shoes and brake-operating mechanism may be mounted on a backing plate or brake shield made to fit against and close the open end of the brake drum. This protects the braking surfaces from dust and other foreign matter.

Some vehicles are fitted with a third type of brake system known as disk brakes. The rotating member is known as the rotor. A brake pad is positioned on each side of the rotor. The brakes operate by squeezing together and grasping the rotor to slow or stop the disk.

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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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