How does a jake brake work? — explained

A jake brake is also known as a compression release engine brake. It is an engine braking mechanism installed in a large diesel engine on semi-trucks. When the jake brake gets activated, it opens exhaust valves in the cylinders after the compression cycle, releasing the compressed air trapped in the cylinders and slowing the vehicle. 

If you use a jake brake when driving on a freeway or downhill, you can add years to the brakes and tires when used appropriately. However, a jake brake result in a loud noise, so using it is prohibited in some areas. 

You can activate the jake brake by removing any application of gas to the engine and then flipping the engine brake switch and allowing the vehicle to slow. In this article, we will answer the question, “how does a jake brake work?”

How does it work?

To enable the jake brake, you should flip an engine brake switch. You can take the pressure off the accelerator to use the jake brake. When you use the clutch or accelerator, the engine brake gets deactivated. It’s similar to how engine braking works in overdrive mode, but many drivers also struggle with the overdrive on or off dilemma just like with how jake brake works.

High amounts of air get forced into the engine cylinders as it enters the intake valve. This makes the air compress, converting it into energy that can be distributed. The vehicle pistons take the energy and direct it to the rest of the vehicle to produce power. 

However, when you activate a jake brake, the air is pushed out of the exhaust valves instead of being used to power the down-stroke and crankshaft. This causes a drag on the crankshaft, slowing the vehicle without any extra friction on the service brakes. Due to how a jake brake operates, drivers should avoid using them on slippery wet roads. 

Jake brakes affect the drive tires, which increases the chances of causing a skid. If you need to use an engine brake to slow down on snowy or icy roads, the tractor will need to get lined up straight, or the truck might skid.

Functions of a jake brake

When you ease the accelerator on a moving vehicle powered by an internal combustion engine, the vehicle’s forward momentum will turn the engine’s crankshaft. The standard compression release engine brake uses an add-on hydraulic system that uses engine oil. 

When the engine brake is activated, the motion of the fuel injector gets transferred to the engine exhaust valve. This occurs close to the engine’s top dead center and releases the compressed air in the cylinder so that energy does not return to the crankshaft. This energy gets expelled out of the exhaust system rather than being retained in the drive train. 

If the jake brake gets appropriately used, a compression release brake can help a vehicle to slow down or maintain speed with little or no use of the service brakes. The jake brake control consists of a multi-position and on/off switch that controls the number of cylinders on which the brake is active. 

The clutch and throttle switches are integral to the system. The activation occurs when the clutch is released with the transmission in gear, and the throttle is released. It is crucial to ascertain the right transmission gear to use depending on the steepness of the grade and the truck’s load.

Limitations of jake brake

The use of jake brakes may cause a vehicle to make a loud chattering or a jackhammer-like exhaust noise, especially trucks with no mufflers or a high flow muffler, causing many states in the U.S, Australia, and Canada to prohibit compression braking within the municipal limits. 

Drivers are usually notified by road signs with some sayings like “Engine Braking Restricted”, ” Brake Retarders Prohibited”, “Jake Brake Prohibited”, “Avoid Using Engine Brakes,” or “Limit Compression Braking” and the enforcement of these signs rules are typically through traffic fines. These Jake Brake prohibitions have led to the development of new mufflers and turbochargers for better silence compression braking noise.

Do jake brakes damage the engine and use more fuel?

When the jake brake is used correctly, it will not cause harm to the engine. Before going for a ride, drivers should ensure that their engine oil isn’t low. If you use an engine brake when the oil level is low, it can cause damage to the engine. 

Drivers should ensure that they let the engine get warm before using an engine brake. If you use a jake brake with a cold engine, it can cause damage. 

It would help if you didn’t allow the truck’s weight going downhill to push the RPMs over the engine’s maximum RPM limit. If you use the jake brakes correctly, it will extend the life span of the service brake shoes and cause no harm to the engine. 

Despite several disagreeing positions that the jake brake uses more fuel, the consensus states that the amount of diesel that might get wasted on jake brakes is worth it to avoid wear. If you are looking to conserve fuel, you should avoid stopping unnecessarily, either with service brakes or jake brakes. 

Irrelevant stops can interrupt the forward momentum of the trunk, and more fuel gets added to get the truck moving again. Coasting into stop signs and red lights is an easy way to conserve diesel.

Jake brake vs. exhaust brake

Jake brakes and exhaust brakes are both brake retarders, but they are potentially opposites in their function. As mentioned earlier, jake brakes release the compressed air trapped in the cylinders. 

In contrast, exhaust brakes trap the engine’s air within the exhaust system. This creates pressure that causes the motor to rotate slowly. Both brake systems have their advantages and disadvantages. 

One prominent opposition to the jake brake system is that it makes a loud noise. People sometimes compare the noise to the sound of a machine gun. Despite the excessive noise Jake brakes give off, it is still compelling and can be an effective tool.

Tips for using the jake brake

• Jake brakes extend the life of the service brake shoes if appropriately used.
• They prevent your service brakes from getting in flames due to overheating and intense friction
• Jake brakes are more effective when running high RPMs in lower gear.
• Several drivers prefer to use the jake brake when descending any incline; staying in low gear allows the jake brake to do most of the braking.
• Drivers can use foot brakes in conjunction with the jake brake.
• Every engine combination and jake brake could be different, so it is crucial to ask your company’s mechanic what the ideal operating ranges are for your truck.
• If you keep the jake brake on all the time, you should slow your speed relative to road conditions to avoid losing traction.
• Jake brakes are not used in slippery or icy conditions, so it is crucial to be aware of weather conditions before using your Jake brake. This is because the drive wheels could lock up and cause a skid. The anti-lock braking system (ABS) does not affect the engine brake.
• The higher the brake setting, the greater the braking power. It is essential to use a lower setting in less optimal road conditions.
• The engine should be at its operating temperature, and the oil should be optimal when using the jake brake.
• Before descending a steep grade, ensure that your jake brake is working correctly by lifting the foot off the throttle.
• Ensure that you pay attention to the “No Jake Brake” signs on the roadsides in areas that prohibit Jake Brakes. This is because the intense noise that the jake brake gives off can disrupt the surrounding area.

Benefits of using jake brakes

• It reduces service brake wear or overheating.
• It is used to maintain a controlled speed, especially downgrades.
• Jake brakes reduce wear on the wheel brakes.
• It lowers associated vehicle maintenance costs.
• It enables you to have improved vehicle control without using the service brake.

Our take

Engine brakes are essential tools for truck drivers when used correctly in the right area. Jake brakes are critical in slowing down vehicles without employing service brakes. 

This generally helps in preserving your service brakes, extending the lifespan of the service brakes, and efficiently reducing cost since the brakes will require maintenance significantly less often.