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Do Semi Truck Trailers Have Brakes? (9 Important Facts)

Semi-truck trailers can often carry massive amounts of cargo. This means their weight can sometimes be extraordinarily heavy.

Have you ever wondered how a semi-truck is able to stop itself, or even keep the trailer stable as it descends a steep hill?

Today we’ll be answering that question, read on to find out…

Here’s the Lowdown on whether Semi-Truck Trailers have Brakes:

Semi-truck trailers have two brakes on each axle. These are air brakes that use compressed air to pressure the brakes and slow down the wheels. With an average weight of 40,000 lbs, trailers need to have brakes to help the truck slow down as efficiently as possible, especially when going downhill.

Do Semi-Truck Trailers have Brakes?

Due to the amount of weight that is carried on semi-truck trailers, they need to have their own brakes. Semi-trucks can take up to two football fields in distance to stop themselves.

If the trailer attached to it did not have brakes, this distance could easily double. Even if the brakes on the trailer were faulty the stopping distance of the semi-truck would increase significantly.

Semi-truck trailers are equipped with air brakes. This means that they are coupled onto the cabin of the truck with air hoses.

Using air instead of a liquid, as hydraulic brakes would, means that multiple trailers can be connected to one another, each with its own set of brakes. Air brakes also allow the trailers to have their own emergency braking systems.

Why do Semi-Truck Trailers have Brakes if the Tractor has Brakes?

Most semi-trucks are used to haul massive amounts of cargo. A fully loaded trailer can weigh as much as 80,000 pounds.

Even with an empty trailer, the truck can still weigh up to 35,000 pounds. This is significantly more than the weight of an average car, which is only 2,871 pounds in comparison.

This extra weight takes much more force to bring to a stop. The basic physics rule that states ‘an object in motion will stay in motion’ applies here.

When that object weighs as much as a semi-truck does, it requires a tremendous amount of braking power to slow it down. Having brakes on the trailer helps to slow down the entire truck.

Semi-trucks take around 40% more distance to stop than the average car. In perfect conditions, this is the length of two football fields.

The brakes need to work hard, but also work together to stop a semi-truck efficiently.

How Many Brakes do Semi-Truck Trailers have?

Semi-truck trailers have two brakes on each axle. This is because the axles are what drives the trailer forward and slowing them down is most effective when braking.

This means your typical 18-wheeler will have a total of 10 brakes. Each brake is used to help slow down the massive weight that is carried on top of the trailer.

This is especially helpful when the semi-truck goes downhill. Going downhill can cause the weight to shift forward, and therefore the trailer picks up speed.

If there were no brakes on the trailer’s axles it would surpass the speed of the tractor and begin to push it down the hill. The driver needs to apply the trailer’s brakes carefully in these situations.

With so many brakes, the braking pressure is split equally between all of them. This reduces the strain on all of them and in turn, they will wear out slower.

What Type of Braking System is Used on Semi-Trucks?

Semi-trucks use an air brake system. This system uses compressed air, rather than hydraulics to pressure the brake pads into stopping the wheels.

Air brakes work with a brake pedal just like the brakes you would find in a car. However, unlike a normal car’s brakes, they do not work instantly.

It takes a second or two for the pressure to be built up before the brake pads begin to clamp down on the discs. Therefore, drivers need to have an air brake endorsement, and without it, they will not be allowed to drive a vehicle that uses air brakes.

Heavy vehicles use air brakes for various reasons. Compressed air is much more readily available, and cheaper. However, the brakes can also be more powerful.

Semi-trucks also have parking brakes and emergency brakes as part of their system. Parking brakes are used to prevent the vehicle from moving or rolling when there is no driver in it.

There are several different parking brakes. The main one is for the tractor, and there are also separate parking brakes for the trailers.

The emergency brakes on a semi-truck will activate when the normal brakes lose air pressure. Some trucks can engage their emergency brakes automatically.

How do Semi-Truck Trailer Brakes Work?

Semi-truck trailers have their own brakes. The trailer’s brakes are hooked up to the cabin and will all be activated together when the brake pedal is pressed.

The brakes work using compressed air. This system is used in many heavy vehicles since they are more reliable, cheaper to maintain and can be stronger than standard hydraulic brakes.

The trailer’s brakes are connected to the tractor using air hoses. Compressed air will be pushed through these lines with huge amounts of force when the brake pedal is pressed down.

The compressed air will then be pushed into a piston. The piston then puts pressure on the brake pads which clamp down on the brake disc.

How Long do Semi-Truck Brakes Last?

The lifespan of the brakes on a semi-truck will depend on how they are used. Different situations can cause the brakes to wear down more.

For example, if a truck drives a route with a lot of downhill sections, it will need to use the brakes more regularly. Thus, the brakes will need to be replaced sooner.

On the other hand, if the driver is gentle with the brakes, the brakes will last longer. Fewer stops often mean less pressure on the brakes.

On average, the brakes on a semi-truck trailer will last around 40,000 miles. However, it can last between 25,000 and 65,000 miles depending on the usage.

How to know if your Semi-Truck Trailer’s Brakes are Worn Out?

Typically, there are some tell-tale signs to identify worn-out brakes. These can often be identified while you are on board.

The air brakes may make it difficult to hear, however, worn-out brakes will make a metallic scraping sound. If you hear this, it could be a sign that the brake pads need to be replaced.

If you find that the brakes are feeling weaker, it might be a sign to get them maintained. Worn-out brakes can result in increased stopping distances.

If you seem to be braking harder or earlier than you usually would, you need to get your brakes checked as soon as possible.

You can also check the state of your brake pads by removing them from the axle. You will see a very thin layer on the inside of the pads. This is the contact area between the pads and the brake discs.

If there is very little contact area left, you need to get your brake pads replaced. Worn-out brake pads will begin to damage the discs if they are still used.

What Maintenance is required on a Semi-Truck Trailer Braking System?

The air brakes found on semi-trucks comprise several different components. These components need to be maintained regularly.

40,000 miles is a good average distance to maintain the brakes on a semi-truck. However, if you can do it more regularly, it is highly recommended.

The brake pads and brake discs need to be inspected for wear and damage. They need to be replaced if they are showing signs of nearing the end of their lifespan.

The compressed air reservoir tanks need to be refilled. This system is what powers all of the brakes, so it is essential to keep it topped up.

The air hoses that connect the trailers to the cabin need to be tested and maintained on a regular basis. If these are not up to standard, the trailer’s brakes will be disconnected.

What are the Best Brake Pads to use for Semi-Truck Trailers?

Air brake shoes come in different sizes and materials. They are categorized based on the Gross Axle Weight Rating (GRAW)

This is the amount of weight that will be over the axle. It is important to have the correct brake shoes with the correct weight rating to ensure safety, brake performance, and durability.

For example, the 20K brake shoe kit is designed for 20,000 pounds of weight over the axle. Therefore, the 23K kit is designed for 23,000 pounds of weight over the axle, and so forth.

Using the correct shoes for your trailer’s weight is essential.

Do Semi-Truck Trailers have Brake Lights?

All semi-truck trailers are required to have brake lights. This is an important safety feature that cannot be overlooked.

The brake lights allow other drivers on the road to see when the semi-truck is slowing down. It will give them time to react and respond to what is happening in front of them.