Couldn’t you just put the truck in neutral and use the regular brakes?
In: 16
Jake brakes change the cycle of the engine so that instead of putting fuel and air in, compressing it, and then having it explode for forward motion, it’s taking in air, compressing it to slow down the engine, and releasing it. The loud noise you hear is the sound of compressed air being released. The new models are very powerful and quiet, the old ones are much louder and truckers sometimes prefer it.
I used to work there. I made DD15 engine parts. Truckers would turn them on on purpose while driving by the plant as a thank you.
A “Jake brake” is just a slang term for an engine compression release (valve). You can use the regular brakes, of course, but when carrying a heavy load, the force applied to the brakes is also heavier, meaning they heat up faster. You can, quite literally, roast your breaks and catch your tires on fire by overusing your brakes while carrying a heavy load, mainly on a downhill descent.
The correct way to approach a long and steady decline, whether in a car or semi truck, is to force your vehicle into an intentionally low gear (for passenger vehicles, 2nd, or L if you don’t have specific options in your automatic) so that the engine and transmission are also sharing the work of keeping you in a controlled descent.
A jake brake (engine compression release valve) is found in very large engines. To put it simply, it lets air out of the engine at a key point in the cycle in order to drastically lower compression, which in turn drastically lowers the engine’s ability to perform work, at a rapid pace. Since it occurs during the *compression* phase, you’re hearing the sound of all the force in that massive engine pushing air out of a (relatively) small valve at full force, which is why it’s so incredibly loud, and banned within many city limits.
# ELI5
> Couldn’t you just put the truck in neutral and use the regular brakes?
Yep. You could do that!
But those regular brakes get HOT the more you use them.
And the hotter they get, the less well they work.
You don’t want to brake during an entire 2-mile hill, because your brakes will overheat and won’t work well at all!
So how else can you slow down the vehicle?
The Jake Brakes also slow you down, but they don’t use the regular brakes. They use the engine to do the braking.
And Jake Brakes don’t overheat like regular brakes do.
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