What Is A Jake Brake?

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Jakes Brake, Jacobs Brake, decompression brake, compression brake, or compression release engine brake are all the same, but what is a Jake Brake?

The Jake Brake creates engine braking in big diesel engines by releasing the compressed mixture of diesel and air in the cylinders right before the compression stroke ends.

Now that you know the basics let’s delve deeper into this nifty tech of the truck industry.

semi truck driving on a highway

What Is A Jake Brake?

Let’s start with a history lesson, the Jake Brake, or engine compression brake (patent name), was designed by Clessie Cummins 1965, founder of Cummins Engines.

The first company to produce the first compression brake was Jacobs Vehicle Systems, where the name Jake Brake or Jacobs brake originated.

It was designed to take the strain off the conventional braking system that is activated by the brake pedal, minimizing maintenance costs and helping maintain a specific speed downhill that is more controlled and safe.

What Does A Jake Brake Do?

The primary function of the Jake Brake is to use the engine compression against itself to slow the vehicle down.

The Jake Brake is controlled through a switch since it alters how a standard four-stroke engine cycle works by opening the exhaust valve close to the top dead center at the compression stroke.

Without the exhaust valve opening in the compression stroke, the air inside the piston acts like a spring and will push the piston back down even without burning fuel.

This scenario has close to no engine braking since there is almost no energy loss through energy transversal.

As we learned in school, energy cant disappear; it just moves from one energy source to another, so how do they mitigate the energy going back into the crankshaft?

The engine dumps the energy out of the engine through the exhaust valve through sound, thus slowing down the vehicle without using conventional brakes.

What is a Jake Brake and How Does it Work?

Why Are Jake Brakes Loud?

As we know, the engine pushes out the compressed air in the compression stroke to gain engine braking.

With compressed air that is forced through the tubing, like a truck’s exhaust, it acts like a trumpet, thus making the typical Jake Brake sound we know of, like in this video.

Kenworth with loud Jakes!

This is an exaggeration; this truck has open exhausts making the sound much louder.

With the loud noises come problems like bans on certain states using them, especially vehicles with no mufflers.

With these limitations, there has been more development into making better mufflers and turbochargers to minimize the sound of the Jake Brake.

What States Ban Jake Braking?

In total, 13 states have regulations on the use of a Jake Brake or engine compression brake.

You can read through these laws in the OLR Research Report.


In California, fire trucks weighing over 31,000 pounds (14,061 kilograms) should be equipped with a retarder (Jake Brake).

Vehicles that emit over 95dB of sound through exhaust will also be ticketed for up to $1,000, and the exhaust system should be fixed within 30 days with proof to mitigate the fine.


In Colorado, all commercial vehicles should be equipped with a muffler if it has a compression brake engine (Jake Brake).

If caught violating the requirements, you will be fined $500.

The states also encourage schools to install electromagnetic or state-of-the-art retarders in their buses.


In Kansas, they prohibit the use of a Jake Brake  on the following vehicle combinations:

  • Truck Tractor
  • Semi-trailer
  • Trailer


In Montana, commercial vehicles equipped with Jake Brakes should have mufflers equipped.

They also prohibit the indiscriminate use of engine brake retarders.


In Oklahoma, they only prohibit indiscriminate use of the Jake Brake, a vague term that can be misinterpreted and abused.


In Oregon, it is against the law to operate vehicles with open exhausts with a Jake Brake on the highway, and one can be fined up to $720.


In Pennsylvania, any vehicle over the gross weight of 80,000 pounds (36,287 kilograms) should be equipped with a Jake Brake or other retarding, compression braking system, and local authority cannot prohibit the use of it unless the Department of Transportation has approved it.

Other States

Arkansas, Delaware, New Mexico, Utah, West Virginia, and Wyoming have regulations prohibiting school buses from having Jake Brakes.

semi truck driving on a b road

Final Thoughts On What Is A Jake Brake

While the Jake Brake is loud, it has a lot of advantages and keeps Truckers safe going down hills and saves transport companies a lot of money by taking some wear and tear away from the regular brakes.

While it might be old tech in the motoring world, it is still amazing how it is still with us today.

Hopefully, you found this article helpful and understand what a Jake Brake is.


Do All Diesel Engines Have Jake Brakes?

No, only big commercial diesel engines have Jake Brakes, like semi-trucks.
Smaller trucks can have something similar to a Jake brake, but it is called an exhaust brake; it works differently by stopping the exhaust gasses from exiting the engine and causing a build-up of compression in the combustion chamber under the exhaust stroke.

Does A Jake Brake Hurt The Engine?

No, since the engine isn’t under load and the exhaust valve relieves pressure in the combustion stroke, it does not affect the engine.
The engine is still rotating at operating speeds; thus, the oiling system functions as usual and keeps oil pressure.

Why Do People Not Like Jake Brakes?

It isn’t because of their function but because of the noise associated with it; the people that install straight-through exhausts also don’t help mitigate this problem.
For the motor enthusiast, we love any sound that an engine can emit except when the engine starts knocking, but most people find the sound irritating.