Our role as a leading provider of truck tarps, cargo control equipment, trailer parts and other trucking supplies gives us the opportunity to speak to a lot of people within the trucking industry. It also gives us the opportunity to explain some of the finer points of how trucks work. For example, we sometimes have to explain that a truck air brake and Jake brake are not the same thing. What confuses people is the fact that the Jake brake releases compressed air when activated.
It’s true that both truck air brakes and Jake brake are related to compressed air in terms of function. But that’s the only similarity. The standard air brake is the truck’s equivalent to the hydraulic brakes on a standard passenger car. The Jake brake is not really a break at all. It is a mechanism that helps slow down a truck by manipulating how the diesel engine fires. Both kinds of brakes are explained below.
Truck Air Brake System
A typical truck air brake system utilizes a combination of storage tanks, pumps, and valves to pressurize and depressurize the system. When the tank is empty, the system is depressurized. This results in brakes being fully deployed. In order to release the brakes, the storage canister must be filled with air. This is what we call recharging. The need for recharging explains why truckers have to let air tanks fill up before they can engage first gear and drive away.
Inside the cab, deploying the brakes works the same way as it does in a standard passenger vehicle. The driver simply depresses the brake pedal to stop the vehicle. What’s different is this: instead of forcing hydraulic fluid into the brakes, depressing the brake pedal releases air from the storage tank, thereby moving a piston that forces the brakes to engage. Releasing the brake pedal allows the system to recharge itself, releasing the brakes.
A Jake brake is a compression release engine brake attached to a diesel engine. Activating the brake opens exhaust valves on the engine to release some of the compressed air inside. This slows the vehicle by slowing down combustion. The Jake brake can slow an idling vehicle substantially.
To understand this better, think of your own passenger vehicle. Even when you take your foot off the accelerator, power is still being transferred from your engine to your transmission and wheels. The only way to interrupt that power is to either shift the car into neutral or shut off the engine. The same is true for big trucks.
The Jake brake slows the truck by reducing the amount of power transferred to the wheels. It allows the truck to slow even when it is still in gear, which is why you might sometimes hear the loud noise caused by a Jake brake as a truck rolls through a lower speed zone. Rather than disengage the gear and apply the standard air brake, a driver may simply choose to take his/her foot off the accelerator and temporarily activate the Jake brake.
The main downside to the Jake brake is that it can make a tremendous amount of noise when deployed. For that reason, some municipalities have limited the use of Jake brakes within their jurisdictions.
As for the standard truck air brake system, it also makes a unique sound. Deploying air brakes tends to make a whooshing sound followed by a hard squeaking. Neither of these noises is terribly loud as long as the system is functioning properly.