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How Do Trailer Brakes Work? 3 Types

Car with MikeGoad, Pixabaytrailer

Trailer brakes work in a similar way to a car’s. Both use friction and convert kinetic energy to heat energy. But having efficient and reliable braking systems on today’s trailers is a journey that began in the late 1800s. Elmer Ambrose Sperry is credited for inventing the first disk brake in 1879, while Edward V. Hartford received the first electric brake patent in 1910.

As years went by, the brake evolved into a complex system that includes high-tech features, hydraulics, and sensors. This article will explain more about how they work.

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The 3 Types of Trailer Brakes

As already stated, the main purpose of a trailer brake is to reduce the momentum of a trailer, which is achieved in many ways.

car with trailer
Image Credit: Gabor Tinz, Shutterstock

1. Electromagnetism

Electromagnetic brakes are modern brakes that use electrical energy to create a magnetic flux. Basically, a magnetic field is created. And based on the principles that like poles attract while unlike poles repel, engineers came up with a braking system.

When activating the brakes, an electrical current flows through a solenoid near the tires, creating a powerful magnetic field. The force attracts an armature which, together with the hub, is riveted on the rotating shaft. This force allows the brake pads to apply pressure on the rotating shaft or drum, slowing the vehicle down.

Another type of electromagnetic brake that also uses electricity is Eddy’s current brake. It is the opposite of the above brake, and instead of attracting the armature, it repels it by creating different electromagnetic fields of like poles. The repulsion force is then used to apply pressure on the rotating drum.

2. Hydraulic Brakes

Hydraulic brakes use a pressurized fluid to exert force on a rotating shaft based on the principle that pressure applied at one area of the fluid is equally distributed throughout the system. For it to work, the system has a brake pedal, master and slave cylinders, levers, fluid reservoirs, brake pads, and high-pressure hydraulic lines.

When the driver applies pressure on the brake pad, it pushes the push rod, which in turn exerts pressure on the piston in the smaller master cylinder. The pressure is equally distributed throughout the system forcing the fluid through the hydraulic lines to the larger slave cylinder. Depending on the design of the system, as the pressure reaches the slave cylinder it is multiplied several times and applies a greater force on the rotating brake pads to stop spinning rotors.

Hydraulic brakes may also be referred to as surge brakes because they are self-adjusting. According to experts, self-adjusting is a term that pulls back brake shoes to their original position after a stop and maintains equal pressure in the fluid.

Another possible reason for the name “surge brake” is when using it, you will notice differences in how the truck and trailer respond. Ideally, the truck responds quicker than the trailer, which is why the latter jerks up after braking suddenly. So, avoid the terrifying experience by applying pressure on the pedals gently.

Image By: MM Stock, Shutterstock

3. Air Brakes

When driving around cities, you may have heard a loud hissing sound coming from slowing down trucks. The unmistakable sound is from air brakes.

The air brake system has an air compressor, valves, high-pressure reservoirs, and air lines. The compressor is driven by the engine using a belt connected to the timing gear. As the compressor sucks in air from the atmosphere, it passes through a series of filters to remove oil and dust impurities. After that, the now-loaded compressor will hold it for some time before releasing it to a cooling coil or air drier to remove moisture before heading to the reservoir.

Once in the reservoir and at a proper pressure level, the braking system is ready for use, and like a hydraulic system, when a driver steps on the pedal, air valves open up. The pressurized air, typically at 100–120 psi, flows to the air-actuated brake pads. The pads apply friction on the rotating drum to stop the trailer.

However, because even small leakages may result in loss of braking power, air brakes have advanced monitoring and control systems. Brakes may be equipped with a manual device to alert the driver when air pressure drops. Besides, a trailer may have several reservoirs to supply air at the required pressure to the brakes and auxiliary system. Furthermore, reservoirs ensure brakes are functional even when the engine is off or the compressor is down.

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What are the Different Types of Trailer Brakes?

Disc Brakes

The disc brake has a disc, caliper, piston, and brake pads. The disc or a rotor disc is connected to the rotating shaft and rotates at the same speed as the tires. Sandwiching the disk are two brake pads. One of the brake pads is mounted on the clipper, while the other is on a piston. Once you apply pressure on the brake pedal, the piston pushes the brake pads, which clamps on the disk to reduce its speed.

Drum Brakes

Drum Brakes
Image By: PongMoji, Shutterstock

While in the disk setup, you can easily see how the brakes are operating; in the drum system, everything is hidden. The complex system consists of a piston, a pair of trailing shoes, a lining, several springs, an adjuster mechanism, and of course, the drum.

When you hit the brake pedal, force is applied to the shoes’ lining (brake pads), and the trailer stops.

In a typical disc brake, pads sandwich the disc but in a drum brake, the shoes clamp on the drum from the inside. For that to be achieved, one of the shoes is mounted on the piston while the other is on a type of pivoting joint known as the adjuster mechanism, which also has springs. The purpose of the springs is to pull back the shoes to their original position after you stop braking.

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Advantages of Trailer Brakes

You are likely to be anxious when driving if you don’t have the right systems in place. However, driving with a trailer shouldn’t be stressful. With the right trailer braking system, you can relax knowing that it’s assisting you in traveling on any route safely.

Trailers’ wide bodies are susceptible to strong wind and poor road conditions. Due to this, they sway when driving. Trailer sway is a huge issue for all drivers since it may quickly turn a pleasant road trip into a major hassle. Trailer brakes can help you effortlessly control a trailer on slippery roads without overstraining the tow trucks’ systems.

When using electric brakes, there’s no jerk or shock. This is important for driving comfort throughout the journey. Additionally, brakes that jerk less protect fragile items in the trailer from moving around.

tiny house trailer
Image By: inrainbows, Shutterstock

Disadvantages of Trailer Brakes

One major drawback to trailer air brakes is that you need special licensing and training in most jurisdictions to drive trailers with air brakes. They also require constant monitoring, inspection, service, and maintenance which increases the cost of running them.

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Frequently Asked Questions (FAQs)

How do trailer brakes work in reverse?

There are no great differences in how brakes operate, irrespective of the direction. They will stop the trailer when reversing in the same way when it is moving forward.

Where do electric trailer brakes obtain power from?

They obtain power from the truck’s battery. On the other hand, the battery is charged through regenerative braking.

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Trailer brakes can be classified according to how they operate, and the most common types are electrical, hydraulic, and air brakes. Air brakes are prevalent despite being among the most expensive systems. But irrespective of which type of brakes is mounted on a trailer, they all absorb kinetic energy using friction to stop it.

Featured Image Credit: MikeGoad, Pixabay


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