What is Jake Braking

I guess we are going to have to go back to the basics here, and “Officially” explain what a “Jake brake” is, and what “Jake braking” is.

Some “Store bought truck drivers” bless their hearts tried to explain to someone on twitter.

This is what I read for the answer given on twitter, “It is a very loud, but helps us to stop. Hard to explain”. This was from another twitter “trucker”, “Brakes won’t stop us we need the Engine Brake or we keep on Trucking.” Nope, unfortunately both the twitter “truckers” are wrong.

The only reason a “Jake brake,” engine brake or engine retarder or exhaust brake would be loud is because the muffler or exhaust pipe is burning/burned out. Or you are running a set of “straight pipes” with no mufflers. The loudness has no effect on stopping. If it did, then the louder it was the better you would stop.

There are two types of “Jake brakes” one is a engine retarder and the other is an exhaust brake, both essentially work for the same purpose, but work entirely different.

An exhaust brake is a means of slowing a diesel engine by closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, slowing down the vehicle. The amount of negative torque generated is usually directly proportional to the back pressure of the engine.

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The term “Jake brake” comes from a Jacobs Engine brake, or engine retarder. It works when exhaust valves in the cylinder head open, releasing the compressed air that is trapped by the head and slows the truck down. When the accelerator is released on the truck, its forward momentum continues to turn the Diesel engine’s crankshaft. That intern compresses air in the cylinder.

As the piston passes through top dead center, the compressed air in the cylinder acts as a spring and pushes the piston back down the cylinder. It returns most of the energy expended in compression back to the crankshaft. This causes the truck to slow down, without the use of the service brakes.

A “Jake brake” is used along with gearing down the truck to keep from overheating the service brakes that are used to stop the truck. Although some trucks are not equipped with an engine retarding system, so gearing down and using the service brakes is required in order to slow or stop.

When a truck’s service brakes are glazed over, this means that they have been very hot, and usually it will make the driver seem he/she has no brakes. Glazing is the hardening of the brake lining, and the only to fix them is to replace or grind the glaze from the lining. The term “Jake braking” is what happens when a driver is using the engine retarder to keep from using the service brakes. Or some truckers say: “I’m saving my brakes, by using the Jake brake.”

When the exhaust system on a truck is in proper working fashion, you barely can even hear the engine brake. But, thanks to “Jake brake cowboys” most communities have added no “Jake brake” use laws. So, the trucks have to comply and use the service brakes on the trucks, in order to slow down and stop. Fines vary from city to city, but I have seen them as high as $400.00.

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  1. Very good explanation Jason . I was taught that although a jake brake is a good thing to have , sometimes they will quit working or they will be very weak so it is always a good idea to know how to gear down and be able to slow the truck without relying entirely on using the jake brake .

    • Thanks Gloria, I agree a driver SHOULD know how to brake a truck down without a “Jake.” But sadly a lot of newbs have only driven with a “Jake” and know absolutely nothing about how to slow a truck without a “Jake.”

  2. Oh , I forgot to add this about engine retarders , they are NOT usually as strong in holding back the truck as a jake brake is although they do a fine job for the most part . I have driven petes with the jake and I drive a freightliner now with a retarder , which took some getting used to after a jake .

    • Yes there are great differences in all of the retarders. Different trucks/retarders will always work differently. I first started driving a coal bucket, I had no jake brake, and was hauling 100,000 pounds…Thats a little much to just depend on the brakes..But I did learn how to stop the thing too without burning up the brakes.

  3. Too many people rely too heavily on their ‘jakes’. One needs to always approach any down grade or stopping situation like they do not have ‘jakes’, shifting down etc. in case the jakes do not engage or are not adjusted properly or they will over wear or over heat their service brakes.

    While ‘jakes’ make our jobs a little easier, they are by no means a necessity if one is a professional trucker and knows what they are doing.

    People who jake in towns need to rethink their way of doing things…jakes are one of the reasons we are not allowed thru towns, they disturb the public and there is absolutely no reason to jake while going thru towns unless it is approaching one in the mountains and there is an excessive grade coming in.

    • Well said, Sandy! I couldn’t agree with you more. Too many drivers think that the Jake Brake “sounds cool”. It is more often considered loud, obnoxious noise pollution. Not to mention misusing it does nothing to impress fellow drivers. Nothing replaces experience, skill, and just plain knowing what you’re doing. The best way to do that is to have an understanding of how and why things work the way they do. With a working knowledge, a professional driver can make better decisions, especially under pressure when lives are at stake. More so, they can avoid these scenerios by being aware of what would put them there in the first place. Comes down to defensive driving and smart driving.

  4. Are there D O T rules that if a tractor has a engine brake on it does it have to work. And if so is this safety related. And if the company will not fix it does D O T allow me to red tag tractor?

    • Check your FMCSR manuel! Federal Motor Carrier Safety Regulation manuel that is. They publish updated versions quarterly. This is the final word in the industry, like it or not.

  5. michael foster
    April 26, 2012 - 9:58 pm

    I have been building automobile and motorcycle engines for years and I either read your article incorrectly or you have a mistake in your explanation of how the Jake Brake works. You stated that it REVERSES the crankshaft rotation when the compressed air/exhaust pushes the piston BACK DOWN the cylinder. If it did in fact do this it would destroy the connecting rod and piston and very possibly the crank shaft in the same way hydraulic locking the cylinder would.

    I think a more accurate description would be that when you close the exhaust the cylinders pressures increase dramatically thereby offering a marked increase in the resistance the piston will encounter during the compression stroke just as a 22-to-1 c/r diesel will slow your vehicle better than an 8-to-1 gas engine will.

    If I am incorrect in this assessment of a Jake-Brake will you please reference the engineering paper that supports your statement.

    • He didn’t say it reversed the rotation of the crankshaft. He said that the engine is no longer providing forward power but instead acting as a brake slowing down the truck. I think you just read it the wrong way.

  6. I live in a city where there are no laws against “jake breaking” but in a neighborhood where there are babies and ill people, a residential area. I wish truckers could understand how frieghtening and awful it sounds to residents when truckers jake or engine break. Sometimes it is as early as 4 am, and then there is the baby to get back to sleep. What a headache!!!

  7. Knock off the damned noise, I relize you drive truck to make a living, but you need to relize you are doing it where we live. My wife works 2nd shift and is woke up early every day. Come on guy ,give her and those like her a break!!!!!!!!!!!!!!!!!!!. not a JAKE.!!!!!!!!!!

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