How Do Diesel Exhaust Brake Systems Work?

Diesel Exhaust Brakes Explained

Are you a seasoned gearhead? Or are you just curious about how trucks stay on the road?

Either way, it helps to know the ins and outs of diesel exhaust brakes and supplemental braking systems and to understand how these essential components keep our roads safer.

Diesel exhaust brakes help trucks slow down without squealing, thanks to some clever engineering that makes efficient use of engine pressure.

It's not just about getting from point A to B. It’s also about doing so safely and smoothly.

So, what does an exhaust brake do? Get the facts on diesel exhaust brake systems. Keep reading to learn more!

Key Summary Points

• Diesel exhaust brakes are supplemental braking systems used primarily in large, diesel-powered vehicles like semitrailers, buses and heavy equipment to assist in slowing down the vehicle without solely relying on the wheel-mounted brakes. They are also available for smaller vehicles through aftermarket providers.
• Unlike compression brakes, which are known for their loud noise, diesel exhaust brakes work by creating additional back pressure in the exhaust system through a controllable physical restriction, which in turn slows down the engine and the vehicle.
• The use of diesel exhaust brakes can extend the life of wheel-mounted braking components like brake pads and rotors by sharing the braking load, especially in heavy, fully loaded vehicles, which also reduces stopping distances.
• Diesel engines lack the natural engine braking effect seen in gasoline engines due to the absence of a throttle valve, making supplemental braking systems like exhaust brakes particularly beneficial for diesel-powered vehicles to prevent wheel brakes from being overwhelmed.
• Training as a diesel technician, such as the programs offered by Universal Technical Institute (UTI), includes learning about supplemental braking systems like diesel exhaust brakes, highlighting the importance of understanding their operation, maintenance and repair for a career in the diesel industry.¹

What Is an Exhaust Brake?

If you’ve ever wondered, “What is a diesel exhaust brake?” you’re not alone. A supplemental braking system, or a diesel exhaust brake system, is an intentionally placed controllable physical restriction within the vehicle exhaust system that creates additional exhaust system back pressure, resulting in a reduction in vehicle speed. The physical restriction comes in the form of a butterfly valve installed in-line in the exhaust system, facilitated by either a servo motor, air pressure or other means.

An exhaust brake is a system placed on large, diesel-powered vehicles that allows for slowing and stopping without using the vehicle’s wheel-mounted brake system. Diesel exhaust brakes can assist the wheel-mounted braking system, therefore extending the useful life of components like brake pads, rotors and brake drums.

Read: 5 Reasons You Should Consider Going to Diesel Mechanic School

Which Diesel Vehicles Use an Exhaust Brake System?

Large commercial vehicles like semitrailers, buses, and heavy equipment, some personal vehicles like large RVs, and tow vehicles have supplemental braking systems (diesel exhaust brakes and/or compression brakes). Exhaust brakes are not a necessity on smaller diesel trucks and passenger vehicles because of their lower weight. Even when loaded, they are not nearly as taxing on traditional brakes.

While not a requirement, many smaller vehicle owners will opt to install them via aftermarket providers. Compression brakes (commonly referred to as Jake Brakes®), which are identifiable by their signature loud “blat blat blat” sound, are an entirely different system.

If the idea of working on diesel systems interests you, including exhaust brakes, you may enjoy a career as a diesel technician. Keep reading to find out more about these braking systems and how you can get trained at Universal Technical Institute (UTI) to prepare for a career in the diesel technology industry.

Read: Becoming a Diesel Fleet Mechanic

Using exhaust brakes and wheel-mounted brakes together

Additionally, the combined use of exhaust brakes and wheel-mounted brakes can reduce stopping distance. Specifically, the stopping distance of heavy, fully loaded vehicles is reduced when both braking systems are used together.

Diesel-powered vehicles do not benefit from the same level of engine braking as gasoline-powered vehicles do. In a typical car or light truck, letting off the accelerator results in speed reduction beyond simple friction associated with moving an object through the air and across a roadway. This slowing is caused by throttle valve closure, creating a vacuum for the engine to operate against.

Diesel engines do not use a throttle valve, as their operation is based on the regulation of fuel, rather than the regulation of air, the latter of which gasoline engines use. This difference in engine design partially explains why diesel-powered vehicles will “coast” for greater distances when the driver releases the accelerator.

Without a supplemental braking option, the combination of heavy loads and lack of engine braking easily overwhelms wheel brakes. Diesel exhaust brakes often are the preferred choice as they provide stopping benefits but without the very loud noise associated with compression brakes. An exception would be heavy-duty vehicles under significant load. In cases like this, compression brakes would be preferred as they provide the greatest braking force.

How Does a Diesel Exhaust Brake Work?

So, how does an exhaust brake work? Essentially, it works by trapping engine pressure in the exhaust system, which forces the engine to rotate slower (back pressure).

Normally, pistons travel upward in their cylinder bore to force spent exhaust gasses out of the engine via the exhaust valve. When the exhaust brake is applied and the inline butterfly valve is partially closed, additional force is required to push the spent exhaust from the engine.

This additional force slows the engine’s rotational speed. As the engine slows, the vehicle decelerates.

In some exhaust brake systems, the vehicle computer controls their operation. In others, the driver can manually actuate the exhaust brake. With either system, the mechanism that closes the butterfly valve may be powered by hydraulic pressure, air pressure or rely on an electronically operated servo motor.

Read: 3 Ways UTI’s Diesel Mechanic Trade School Can Prepare You for a Career

What makes exhaust brakes efficient?

• Taking advantage of existing systems in the vehicle.
• Not needing to be factory installed, as aftermarket applications exist.
• Simplicity and no need for a hydraulic brake line or pneumatic air pressure to the wheels to stop the vehicle.

What makes exhaust brakes beneficial?

• Keeping wheel brakes from overheating.
• Quiet, unlike compression brakes.
• Requiring minimal upkeep while remaining effective.

Read: What Skills Can I Learn at Diesel Mechanic School?

How does this apply to a career?

Many diesel-powered vehicles have supplemental braking systems, such as exhaust brakes. As a diesel technician, familiarity with their use and operation is important for your career. The braking systems require occasional maintenance, and some users report decreased effectiveness over time. Properly inspecting, diagnosing, repairing and maintaining exhaust brake systems are important skills to have and can take mechanics far in this industry.

Read: UTI Grad Angela Barbosa: A Change in Careers Changed Her Life

Diesel Exhaust Brake FAQs

1. What is the purpose of an exhaust brake system?

The primary purpose of an exhaust brake system is to aid in controlling the speed and providing additional braking power to vehicles, particularly those with diesel engines, when descending steep slopes or navigating downhill terrain.

2. What are the benefits of using an exhaust brake system?

One primary benefit is enhanced control and improved safety when navigating downhill slopes or carrying heavy loads. The system minimizes brake fade, heat buildup and wear on the braking components, extending their lifespan and reducing maintenance costs. Additionally, the exhaust brake system aids in maintaining a consistent speed while descending steep grades, ensuring better stability and handling of the vehicle.

3. Are there different types of exhaust brake systems available?

Yes, there are various types of exhaust brake systems designed to suit different vehicle configurations and engine types. The most common types include pneumatic, hydraulic and electronic exhaust brakes.

Pneumatic exhaust brakes function by restricting the exhaust flow through a butterfly valve in the exhaust pipe, creating back pressure to slow down the engine. Hydraulic exhaust brakes use a similar principle but use a hydraulic piston to restrict exhaust flow. Electronic exhaust brakes, on the other hand, use electronic controls to modulate the exhaust system, providing precise braking force adjustments and integration with the vehicle's engine control unit (ECU).

4. What is the difference between a diesel exhaust brake and a traditional exhaust brake?

The primary difference lies in their application and design aimed at different engine types. A diesel exhaust brake is specifically designed for diesel engines, using back pressure created in the exhaust system to slow down the vehicle. In contrast, traditional exhaust brakes can be used in both gasoline and diesel engines but may not provide the same level of effectiveness in a diesel context due to the absence of a throttle valve, which plays a significant role in how braking is achieved.

5. How does a diesel exhaust brake improve vehicle safety?

A diesel exhaust brake significantly enhances vehicle safety by providing additional braking power, especially on downhill terrains where heavy loads may overwhelm the wheel-mounted braking system. By reducing brake fade and maintaining consistent vehicle speed, the exhaust brake allows for better control and handling, minimizing the chances of accidents or loss of control during critical situations. This supplementary braking capability not only extends the lifespan of traditional brakes but also contributes to a safer driving experience.

Read: UTI Graduate David Hopf Finds a Clear Career Path in Diesel

Train for a Career in Diesel

Students can learn the hands-on and theoretical fundamentals they need for a diesel career in our 45-week Diesel Technology program!^1,7,18 We can teach you the knowledge and skills needed to service powerful trucks and engines, including diesel exhaust brake systems.

Your training doesn’t have to stop there, though. We also offer a variety of diesel-specialized training programs, which were created in collaboration with leading brands!

To learn more, request information online or call us at 1-800-834-7308 today. We’ll connect you with an Admissions Representative who can help you get started!