The jake brake takes its name from the manufacturer who invented the most common implementation of the technology, the Jacobs Company. The jake brake is an add-on engine brake for diesel engines. Big trucks can weigh as much as 80,000 pounds. Stopping them or slowing them down results in a great deal of wear on the brakes, which have to be replaced frequently. The jake brake, as an engine system, causes no wear and tear and can help slow the truck before the wheel brakes need to be applied.

When the driver presses a button in the cab to activate the device, two things happen. First, the switch excites the engine brakes’ solenoids. By itself, this would help only a little but it is necessary for the second step. What happens inside of the engine goes roughly like this.

The jake brake stops the flow of fuel to the pistons. With the fuel flow interrupted, the piston is compressing air. The jake brake opens the exhaust valve just as the air reaches maximum compression, dumping all of that energy in an almost instantaneous explosive release. The result is a very effective slowing of the vehicle as mechanical energy is converted to heat and then dumped. The jake brake transforms the internal combustion engine into an air compressor with a loud release.