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Brakes may be the most critical system on your vehicle. The ability to stop, and maintain control of your vehicle while doing so, can be the difference between an uneventful trip and a white-knuckle experience. All brake systems work by converting the kinetic energy of your moving vehicle into heat through friction. This friction will slowly remove material from the friction surfaces, and whether your brake system is hydraulic, or air operated, both systems will have wear items that need to be monitored and replaced as they are depleted. Brake rotors, brake drums, brake pads, and brake shoes are the friction surfaces that will all wear as the brakes are used.

Hydraulic brakes

Hydraulic brake systems can be found on light and medium-duty vehicles. Hydraulic brakes use hydraulic fluid to transfer the energy from your foot proportionally to the brake at each wheel. This force is used to activate drum brake wheel cylinder or disc brake calipers.

Air brake systems

Air brake systems are used on heavy-duty trucks and trailers. Using compressed air allows brake signals to be transmitted long distances without losing effectiveness and provides fail-safes that add a safety factor to the heavy loads and high demand that air brakes face. Vehicles with air brakes will have an onboard engine driven compressor that replenishes the air as it is used. Air tanks on trucks and trailers provide a reserve of available air and air dryers condition the air to protect the valves that are used to control the flow and behavior of air signals. Air brake systems are more complicated than hydraulic, but the air system on a truck and trailer can be used for other tasks beyond stopping the vehicles.

Disc Brake System components

Air and hydraulic brakes will be similar in appearance at the wheel end with both types of brakes having a disc brake option and a drum brake option.

    Brake pads - Brake pads consist of steel backing plates with a friction material bonded or riveted to them. The type of friction material and its aggressiveness are determined by the vehicle application and its intended usage. The brake caliper will clamp the pads against the rotor, and the friction material generates friction to bring the vehicle to a stop.

    Disc brake calipers – Convert hydraulic or air pressure into clamping force. The caliper squeezes the brake pads onto the brake rotor creating the friction needed to stop the vehicle. On a vehicle with air brakes, a brake chamber will convert the air to mechanical force and actuate the caliper.

    Brake Rotors – Brake rotors, also known as brake discs, are the most common braking system in use today. The rotor spins between disc brake pads which are clamped to the rotor when the brakes are activated. Disc brake rotors are made of steel, and they are a planned wear item in disc brake systems. Even though the rotors are a much harder material than the friction surface of the brake pads they will also wear, although at a slower rate.

Drum Brake systems

Drum brakes are an older style of brake system that is most commonly found on the rear of light and medium duty vehicles with discs on the front. Drum brakes may be found at both the front and back of older vehicles and most Heavy-duty trucks and trailers although, disc brakes are quickly becoming the standard on new HD trucks and trailers.

    Brake Drums – Brake drums are bowl-shaped, and the friction surface is on the inside of the drum. From the outside, the drum will be the only visible part of the brake system, even with the wheel off. When the vehicle is moving the drum spins around the brake shoes, and when the brake is applied the brake shoes are forced outward into the friction surface of the drum. Properly inspecting drum brakes required the removal of the drum.
    Brake Shoes – Brake shoes are steel with a friction material bonded or riveted to the surface. Brake shoes will be curved to match the inside diameter of the drum. Brake shoes have a larger surface when compared to brake pads, so they will tend to run cooler as less force is required to generate the same stopping power. Drum brakes have the disadvantage of requiring return springs to pull the shoes back into a released position when brake pressure is removed.
    Hydraulic drum brake wheel cylinders – Wheel cylinders use the hydraulic pressure to push the brake shoes apart and into the brake drum. Return springs in the wheel end pull the shoes back to a released position and return the pistons in the wheel cylinder.
    Air brake camshafts – Brake cams are used to actuate the brake shoes on an air brake system. Brake cams are generally referred to as “S Cams” as the end has an “S” shape used to push the shoes farther as the cam is twisted more.
    Air brake slack adjusters – Slack adjusters are used on air brake systems to compensate for wear of the brake shoes and drums. Hydraulic systems will not use a slack adjuster as the fluid automatically compensates for wear.

By properly maintaining and servicing your brake systems, you can keep your vehicle reliable and safe. Here at Michigan Truckspring, we have the parts and knowledge to help keep you on the road. Thoroughly checking the brakes during vehicle services and replacing worn components when they reach their minimum thicknesses will ensure your vehicle stays on the road.

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