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A brake drum forms a friction pair with the brake shoe lining, slowing or stopping the rotation of the wheel and axle. They also collect and release heat during braking.
One indicator of a problem is if the drum shows signs of bluing, which may indicate a severe overheating of the surface. This could be the result of hard braking or improperly functioning return springs.
Brake Shoes
Brake shoes are a major part of drum brakes and work by pushing outward against the inner surface of the brake drum. The friction that results causes the vehicle to slow down and eventually stop.
They are made of special materials that can withstand the high heat and friction that they produce. Those materials include various types of fibers as well as synthetic aramid. Field experience as well as chemical and material engineering allow constant advancements in the design and manufacture of brake shoes and pads to improve functionality and reduce maintenance costs.
Each drum brake assembly consists of one leading and one trailing shoe. The shoes are pushed into contact with the brake drum’s inner surface by hydraulic pressure from the wheel cylinder. The pistons housed in the wheel cylinder displace outward when the brake pedal is pressed, sending hydraulic fluid to each brake shoe. The dual twin leading shoe type features pistons that can displace in two directions, allowing the brake shoes to function as the leading ones no matter which direction the car is moving. This is the type typically found on front drum brakes in small- to midsize trucks.
Brake Cylinder
The brake master cylinder is the heart of your drum and disc brake system. When you step on the brake pedal, a rod is pushed into one end of this sealed cylinder, which contains fluid and pistons that work like plungers to pump the brake fluid through lines toward the wheels.
The cylinder has two exits to push the brake fluid through diagonally opposite wheels and into slave cylinders located on calipers that press friction pads onto the rotor. The advantage of this layout is that the brakes are self-energizing — boosting their stopping power without increasing braking pressure.
Brake drums should be inspected regularly for signs of excessive wear, especially near the lining rivet holes. Excessive wear is a sign of the drum not being properly rated for your vehicle and application. Also watch for heat checking, which appears as fine hairline cracks in the braking surface. This condition can result from repeated hard braking, or brake system imbalance that causes the drum to be continually heated and cooled.
Brake Pads
The brake pads or shoes (on drum-braked cars) are a crucial part of the system, converting kinetic energy to thermal energy by applying friction between them and the rotor. They wear down with normal use and need to be replaced when the remaining friction material becomes too thin to continue slowing the rotor properly. Without a fresh set of pads, the metal pad mounts and rotor can start wearing down, too — which will result in damage to additional parts of the brake system.
Most new car models come with pads that feature a small attachment that acts as a wear indicator – a sensor that triggers a dashboard warning light or makes a screeching sound when the remaining pad material gets too low. Some drivers may also notice that their brake pedal begins to pulse, which is another sign that the pads need replacing. Brake pads can be made from a variety of materials, with organic (natural rubber or synthetic compounds) and semi-metallic being the most common for passenger vehicles.
Brake Hoses
Brake lines transfer hydraulic pressure from the master cylinder and proportioning valve to your wheel calipers, applying force that brings your brake discs or drums into contact with each other to slow your vehicle. They are critical for keeping your car safe, and like all components they will eventually wear out, becoming frayed or leaking. Rubber hoses can also swell due to moisture absorption, reducing the line pressure and affecting your braking efficiency over time. Stainless steel hoses are more rigid and durable, resisting swelling to ensure your car’s braking power is always at its peak.
Brake hoses can be very hard to detect when they have developed issues, but one of the most common symptoms is a mushy or spongey brake pedal. Any sort of leak that reduces the hydraulic pressure in the braking system is a dangerous situation and needs to be addressed as soon as possible. It is best to have them replaced by an expert mechanic, such as those at RepairSmith.
