Jake Brake

Diesel engine compression brake is used to slow down a large trucks. It is most often associated with semi-trailer trucks.

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Commonly referred to as Jake Brakes because Jacobs Vehicle Systems is the original developer of this type of braking system.
The Jake brake or compression brake works by using hydraulic pressure to momentarily open the exhaust valve at the end of the compression stroke, venting off the compressed air into the exhaust system. That’s where all the noise comes from. The braking of a Jake brake occurs because of the pumping loss compressing the air, and then eliminating the compressed air “rebound” on the power stroke. Additionally, there’s a pumping loss as the piston descends on the power stroke with both valves closed and no combustion.

 The Jacobs Engine Brake is a “compression release” engine brake on large diesel trucks, especially useful on steep downhill grades.
To understand how it works, remember that a diesel engine has much higher compression than a gasoline engine. The Engine Brake brake slightly opens the exhaust valves when the piston is near top dead center (where ignition would normally occur). On the upstroke, the piston compresses the air in the cylinder  creating resistance in the engine. The Engine Brake then releases the compressed air, and the energy stored in it, before it can push back on the piston. In addition, releasing the compression prevents any fuel in the cylinder from igniting. (diesels don’t have spark plugs like gasoline engines – they rely on high compression to ignite the fuel.) So, you’ve got drag on the upstroke, no power on the downstroke.

The explosive effect creates a good deal of noise, although the Jacob’s Company believes that with its brake, the noise is caused not by the engine brake itself but by irregular modifications or ineffective maintenance of the exhaust system.

Truckers use the compression brake in order to slow the truck down especially on steep hills or downgrades. Regular heavy duty truck brakes can often become too hot when trying to stop the momentum of an 80,000 pound truck and trailer moving downhill, and the Engine brake is a valuable tool in helping to slow a truck.

Some areas have implemented ordinances disallowing the use of this device due to the loud noise it can make as it slows the engine.
Not only is this an issue of contention for truckers because of safety concerns, but it is also an issue for the Jacob’s Company. The Jacobs brake people go so far as to ask anyone seeing these “brand specific” signs to E-mail the location to them.

Benefits of  diesel engine compression braking:

  • Capable of 85% of vehicle braking needs
  • Enables faster downhill control speed
  • Reduces slowing time/distances on flat land, slowing a heavily loaded vehicle from 90 to 70 kph in 30% less time and distance
  • Significantly reduces brake lining wear –  Lowers cost of ownership

The Exhaust Brake is another, quieter method of engine braking on a diesel truck. This device partially closes off the exhaust, so the air pushed out through the exhaust valve on the exhaust stroke is restricted, slowing the engine and the vehicle.

Some trucks now employ both compression and exhaust braking to reduce Stopping distance.


At R and M Diesel in Sheridan, Arkansas we can service, repair, replace or install a Compression brake on your diesel truck.

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