Wheel Cylinder

The Brake System:

The Wheel Cylinder

The wheel cylinder changes hydraulic pressure into mechanical force that pushes the brake shoes against the drum. The wheel cylinder housing is mounted on the brake backing plate. Inside the cylinder are two pistons which are moved in opposite directions by hydraulic pressure and which, at the same time, push the shoes against the drum. The piston or piston stems are connected directly to the shoes.

Image Right: Wheel Cylinder

Rubber piston cups fit in the cylinder bore against each piston to prevent the escape of brake liquid. There is a

light spring between the cups to keep them in position against the pistons. The open ends of the cylinder are fitted with rubber boots to keep out foreign matter. Brake fluid enters the cylinder from the brake line connection between the pistons. At the top of the cylinder, between the pistons, is a bleeder hole and screw through which air is released when the system is being filled with brake fluid.

On some vehicles, a stepped wheel cylinder is used to compensate for the faster rate of wear on the front shoe than on the rear shoe. This happens because of the self-energizing action. By using a larger piston for the rear shoe, the shoe receives more pressure to offset the self-energizing action of the front shoe.

If it is desired that both shoes be independently self-energizing, it is necessary to have two wheel cylinders, one for each shoe. Each cylinder has a single piston and is mounted on the opposite side of the brake backing plate from the other cylinder.

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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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