What is the function of automotive brake shoes?
2 Answers
Brake shoes function in conjunction with brake drums to achieve braking. The brake drum rotates with the wheel, while the brake shoe is connected to the axle via the brake backing plate and remains stationary. During braking, the brake shoe is pressed against the brake drum by the brake operating mechanism, utilizing the friction between them to decelerate the wheel until it comes to a stop. For passenger cars and light-duty, mini, and medium-duty trucks, brake shoes are commonly made from T-section rolled steel or stamped-welded steel plates. Heavy-duty trucks and larger vehicles use brake shoes made from materials such as malleable cast iron, ductile cast iron, cast steel, or cast aluminum alloy, with cross-sections shaped like I-beams or mountain profiles. The cross-sectional shape and dimensions of brake shoes should ensure good rigidity. However, in small vehicles, steel brake shoe webs may have 1-2 radial grooves to slightly reduce bending stiffness, ensuring even contact pressure between the brake shoe friction lining and the brake drum, thereby reducing brake squeal. The thickness of the brake shoe web and flange varies by vehicle type: approximately 3-5mm for passenger cars and 5-8mm for trucks. The friction lining thickness is about 4.5-5mm for passenger cars and typically over 8mm for trucks. Friction linings can be riveted or bonded to the brake shoe. After attachment, the outer surface of the friction lining is machined to specified dimensions and roughness. Bonding allows for greater wear thickness (usable down to a limit of 1-1.5mm), but replacing the friction lining is difficult, often requiring full brake assembly replacement. Riveted linings are easier to replace and produce less brake noise, but usable thickness is limited by rivet protrusion, making them suitable for linings thicker than 6.5mm.
Automotive brake shoes play a crucial role in the braking system. Simply put, they are the core component of drum brakes. When you press the brake pedal, the hydraulic system pushes the brake shoes outward, causing them to rub against the drum inside the wheel. This friction directly slows down or stops the wheel, giving drivers a sense of control. Many people mistakenly believe they are only suitable for older vehicles, but in fact, they are still commonly found in some modern compact cars or rear wheels due to their low cost and easy installation. However, wear issues must be noted; when the shoe lining wears thin, braking effectiveness weakens, leading to longer stopping distances. Checking them during regular maintenance can prevent safety hazards. While driving, if the brakes feel spongy, it's likely the brake shoes need replacement. Though small, they are vital for driving safety and should never be neglected.
