Jake Brake

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, releasing the compressed air trapped in the cylinders, and slowing the vehicle. Although Jake brake properly refers to the Jacobs brand of engine brakes, the term has become a genericized trademark and is often used to refer to engine brakes or compression release engine brakes in general, especially on large vehicles or heavy equipment. They are often not allowed in to be used in towns as they create loud, clattering noises.