Compression release engine brake
![Jacobs Engine Brake Division logo.](/Images/godic/202501/21/Jacobs_engine_brake_division_badge_0014349.jpg"){kind=icon}
![A view of engine compression brake rocker arm (on the left).](/Images/godic/202501/21/Unit_injector4349.jpg")
![A Jake Brake from Jacobs Vehicle Systems.](/Images/godic/202501/21/Jake_Brake4349.jpg")
A compression release engine brake, frequently called a Jake brake or Jacobs brake, is an engine braking mechanism installed on some diesel engines. When activated, it opens exhaust valves in the cylinders after the compression cycle, releasing the compressed air trapped in the cylinders, and slowing the vehicle.