Few optional products for a light- to medium-duty diesel vehicle offer as much payback potential as an exhaust brake. Properly installed, an exhaust brake can reduce the wear and maintenance requirements for service brakes, often as much as doubling their original service life. In addition, tires and critical engine parts have demonstrated increased reliability characteristics on recreational vehicles equipped with an exhaust brake. Additional benefits include less vehicle downtime, enhanced driver confidence and safer operation.
The primary purpose of the exhaust brake is to quickly control vehicle speed under a variety of operating conditions. The slowing power of an exhaust brake is achieved by restricting the flow of exhaust gases and increasing back pressure inside the engine. This increased back pressure creates resistance against the pistons, slowing the crankshaft's rotation and ultimately helping to slow a vehicle's momentum. An exhaust brake is capable of harnessing as much as 100 percent of an engine's positive power for use in slowing the vehicle.
Fleet managers should avoid using exhaust brakes on gasoline-powered engines. The typical gasoline engine does not have enough muscle to handle a supplementary braking system. On the other hand, a diesel engine - with its turbocharger, high torque outputs, robust design and overall greater efficiency - is ideally suited to handle everything that an exhaust brake can offeIt should be cautioned, however, that not all diesel engines are going to work well with an exhaust brake. Exhaust brake performance is a function of camshaft profile, cam timing, spring rates and the mechanical limitations of the engine. Some engines have lower psi ratings (also known as back pressures), which are responsible for slowing down the vehicle. For example, some diesel engines offer 60 psi, while others as little as 15 psi. A lower psi rating, such as 15, will generate only a limited amount of supplemental braking performance no matter what the exhaust brake is rated.
It is important to note that each diesel engine is different and takes specialized components, thus exhaust brakes should be tailored for specific applications.
One way to help ensure that an exhaust brake is properly engineered is to make certain that the engine manufacturer has approved the brake and has a qualified dealer to install it as they understand its effects on their specific engine. This is especially important on Cummins engines, for example, because the exhaust valve springs need to be changed in order to install the brake.
Another factor influencing the decision for an exhaust brake is its warranty. Exhaust brake warranties are important because most exhaust brakes are located in a potentially destructive environment that results from road debris and heat. Any warranty should also cover progressive engine damage.
Despite warranties, malfunctions can occur, but what happens after a malfunction is another important consideration in brake selection.
If an exhaust brake fails in the "closed" position, the engine as well as the brake will often be disabled, meaning that the vehicle would have to be towed to a repair facility.
Many exhaust brakes have been designed and built with features that permit the products to fail in the "open" position, which still allows the engine to function and the vehicle to operate. Also, it should not matter whether the brake's actuation device is electric, pneumatic, vacuum or hydraulic. Each device should open once the actuation source is removed, thus allowing the engine - and vehicle - to operate even though the exhaust brake may not be functioning.
A frequently asked question among potential exhaust brake users is will it work with an automatic transmission? The answer is yes. Typically, a turn of a dash switch to the "on" position and the brake is enabled. The brake is turned off by stepping on the throttle.
There are essentially three different types of automatic transmissions: without a lock-up converter, with a manual lock-up converter, and electronically controlled. In each case, a properly selected and installed exhaust brake will not damage an automatic transmission.
Exhaust brakes working with manual lock-up transgressions can experience some loss of retarding power in the transmission's converter. When the brake is engaged, most of the retarding effect will occur during lock-up. Maximum performance is usually experienced after manually downshifting. An electronically controlled automatic transmission selects a lower gear to bring the engine up to maximum rpm for maximum retarding horsepower. When the vehicle starts to slow down, the transmission will select a lower gear, and continue to do so down to second gear. This feature is well liked by operators, because the function is automatic.
