How Exhaust Brakes Work

Diesel Engines Only

Exhaust brakes work on a diesel engine to help slow the vehicle down without putting undue strain on the actual wheel brakes. Because these engines do not have a throttle valve present on the intake manifold, there is a total lack of vacuum inside the engine when there is no fuel flowing, such as when the driver lets the accelerator up during motion. This intake vacuum creates the "slowing down" effect felt in passenger cars and trucks when going downhill with no accelerator applied.

How They Work

An exhaust brake literally closes off the exhaust manifold from the engine via a valve, creating huge amounts of backpressure in the cylinders, which slows the pistons down, which in turn slows the engine down. In this manner, drivers of diesel cars and trucks are able to safely add stopping power while saving wear and tear on the wheel brakes. The more the exhaust pathway is closed up, the more torque is used to brake the vehicle. Some exhaust brakes can be integrated with a turbo system, and some are stand alone.

Things to Know

An exhaust brake is not the same as a "Jake Brake", which uses valve retardation and compression to slow the engine down. A Jake Brake is much louder than an exhaust brake, and some communities have banned the use of them altogether. Big semi tractor trucks employ this braking system often. It sounds somewhat like a machine gun when in use, which is why they are banned in some places. "Jake Brake" is actually just a widely accepted name of the compression braking system made by Jacobs, but other brands do exist. Some of the new exhaust brakes that are coming out employ a modulation system which enhances braking performance across the entire RPM range of the engine. If you are looking to add an exhaust brake to your diesel-engine automobile, it is highly recommended to let a professional handle it, unless you have adequate knowledge and experience of diesel exhaust systems.