If you’re driving on the highway, you may eventually come across a “no engine braking”, “engine braking prohibited”, or “no Jake brake” sign, especially as you get closer to more urban areas. You may have been wondering what exactly those signs mean, and whether or not they apply to you.
Fortunately, unless you’re driving a semi or some other large commercial truck, you don’t have to worry about not using your engine brake because your car probably doesn’t have one to begin with. The use of the engine brake is prohibited in some places because of the loud noise it makes.
Today, we’ll be talking all about engine brakes and covering what they are, how they work, and why exactly they’re illegal in some places.
What Is Engine Braking?
Engine braking, as the name suggests, is the practice of using the engine to slow a vehicle down instead of the actual brakes. There are actually two types of engine braking that exist; the kind you can do yourself in a manual transmission car, and the kind that commercial trucks use.
The first kind of engine braking is actually totally legal no matter where you are, because it doesn’t work the same way as the kind of engine braking used in commercial vehicles. As you probably know, you can increase your speed in a manual transmission car by shifting up a gear, and you can also decrease your speed by shifting down.
That’s basically what engine braking in a normal car is. Without pressing the brakes, you take your foot off the gas, change gears, and slowly release the clutch. Because you’re going into a lower gear, the car will slow down without you having to actually use the brakes.
Engine braking in this way isn’t too difficult to figure out, but you may have to practice a few times before you get it right; timing is important in order to do this as safely as possible.
So why is engine braking even a thing when normal brakes exist? There are a couple of reasons why it might be preferable to use an engine brake on occasion. For one, using an engine brake helps preserve the longevity of your actual brakes, since you’re not using them all the time.
If you’re driving a particularly large and heavy vehicle, it’s only natural that your brakes are going to wear out quicker because they’re being asked to do more work. Engine braking doesn’t generate very much extra friction in any of the drivetrain components and lets drivers use the regular brakes less frequently.
For commercial vehicles, engine braking is particularly useful when going down a steep hill. If a commercial vehicle used its regular brakes on a steep hill, the added momentum from the pull of gravity can put a lot of friction on the brakes and cause brake fade very quickly. With engine braking, this situation is avoided.
How Does an Engine Brake Work?
We mentioned that commercial vehicles use a different kind of engine braking than what you’d use in a regular passenger vehicle, so let’s talk now about what exactly that is and how it works. The kind of engine brake you’ll find in commercial vehicles is sometimes referred to as a compression release brake, or more commonly, a Jake brake.
The term “Jake brake” refers to Jacobs Vehicle Systems, the company that first invented this type of engine brake. Other companies these days make similar systems, but it’s common to see all of these systems referred to as Jake brakes regardless of who makes them.
To understand how a Jake brake works, it helps to know how an engine works. Normally, air and fuel enter an engine’s combustion chamber and are compressed and ignited. The ignition creates a force that moves the piston in the cylinder, which in turn rotates the crankshaft and drives the wheels.
When the Jake brake is activated, however, this does two things; it cuts off the fuel supply to several of the cylinders, and it opens the exhaust valves of these cylinders during the compression stroke. The engine continues to turn, but because combustion isn’t happening, the engine starts to slow down.
The unused air that gets pulled into the engine while the Jake brake is activated is then sent right out of the engine again during the compression stroke. This is what produces the characteristic sound of a Jake brake; the air being forced out of the exhaust valves.
Why Is Engine Braking Illegal In Some Areas?
If you’ve seen a “no engine brake” sign before, you might have assumed that these signs were in place because engine braking is a dangerous practice. This is decidedly not the case; in fact, using engine brakes can actually be safer than using regular brakes, depending on the circumstances.
In actual fact, engine braking (specifically the use of a Jake brake on commercial vehicles) is illegal in some areas because of the noise it makes. If you’ve spent any time around commercial vehicles, you’re probably familiar with this sound already; it’s the loud, rapid-fire “blat-blat-blat” noise you sometimes hear big trucks make.
If you’re not familiar with this noise, it sounds pretty similar to something like a jackhammer or even a gun firing. Modern Jake brake systems use mufflers to reduce the volume somewhat, but even then, Jake brakes still produce about 80-83 decibels when used.
The banning of Jake brakes in some areas has proven to be controversial, however. Those in favor of banning Jake brakes argue that they generate excessive noise and are disruptive to the surrounding communities. Those opposed to banning Jake brakes argue that they’re an important safety feature that should be allowed to be used more frequently.
Frankly, it’s easy to see where both of these groups are coming from. Jake brakes are indeed pretty loud, and it would be pretty irritating to hear them being used near your home during all hours of the day. However, the fact of the matter is that using a Jake brake stops the regular brakes from wearing down so quickly, and thus has tangible safety benefits.