I tried to Google engine brakes after seeing all the avoid use of engine brake signs and now I’m more confused. Can someone explain what engine brakes are, what Jake brakes are (if they are different), and why they are loud. Thanks.
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engine breaking is stepping off the accelerator and changing to a lower gear than appropriate for the speed of the car to use the vacuum/compression in the cylinders and friction in the drive train to slow the car, the point is to avoid wearing out the brakes and also old brakes weren’t so powerful, it doesn’t really apply to new cars but it’s useful to know how in case your brakes should fail. Jakes brakes are similar but a more deliberate system installed in diesel cars https://en.wikipedia.org/wiki/Compression_release_engine_brake
Engine brakes ( or Jake brakes , a name brand ) essentially turn the engine into an air compressor. What it does is shut off the fuel to the cylinders and makes them compressor air. The act of compressing the air takes energy, and the energy comes from the momentum of the truck. So ass the engine compresses air it slows the vehicle down without using the brakes at the wheels. This is particularly effective going down hills where continued use of wheel brakes causes them to fade ( lose friction ) and overheat. Both conditions cause brake failure.
Typically automobiles are propelled by internal combustion engines, machines where a fuel is mixed with air and burned to produce a controlled explosion. That explosion takes place in a sealed container, a “cylinder”, and the force of that explosion pushes a piston to provide the motive power to the engine. Broadly speaking the process happens in a series of four steps: **Suck, squeeze, bang, blow.** The engine sucks air into the cylinder along with fuel, squeezes that mixture down into a more compact state, ignites it to cause the explosion (bang), and then blows the exhaust out of the cylinder to ready it for the next cycle. Compressing the air is called the “compression stroke” and extracting the power from the expansion of the explosion is the “power stroke”.
A Jake brake (or engine brake) changes this basic process by opening the exhaust valves right before the compression stroke ends, releasing the energy used to compress it and slowing the engine. Since the engine is connected to the wheels by the drive train this results in the vehicle slowing as well (assuming it is in gear). This is in contrast to a normal brake which is just creating friction by squeezing brake pads onto a rotor. Unfortunately releasing high pressure air straight out of the cylinders is very loud, like popping a balloon.
When you are driving around, have a gear in and let go of the accelerator pedal, the car will still continue moving because of its inertia. The engine, however, isn’t delivering power to the wheels to speed up or maintain speed anymore. Instead, it’s being dragged by the turning wheels and the inertia of the car, effectively causing a braking force, unless you’re using a classic torque converter automatic. Making deliberate use of this force to slow down the vehicle or to manage speed down a descent is making use of the engine brake. Typically, at higher rpm the effect is greater, which is why using the engine brake could be noisy.
On heavier vehicles, there are a number of different systems in use to aid this effect or to amplify it. The jake brake on diesel engines uses the air inside the cylinders and the timing of the valves to obtain more braking force. This also comes with its own noise.
They are the same, just like Kleenex is facial tissue: Jake Brakes is a brand name that is usually associated with it but legally if you say “No Jake Brakes” and some joker comes by with something that does the same job and has the same flaws but isn’t made by the same company, well, it’s not a Jake so you can’t stop him. If you say No Engine Brakes that covers both the original and the imitators.
Now, what is it. On large trucks that have large diesel engines, you can slow down by the same kind of disc and drum hydraulic brakes your regular car uses, just scaled up- but those wear out over time or worse, can overheat and fail.
Or you can make your engine do its job backwards, forcing the cylinders to compress air then vent it out, dumping energy in the process. Of course, this does not go through the muffler system and thus makes a loud, distinctive rattling [sound](https://youtu.be/jgl9Y351rok?si=ADp3097vHw7AdU01)
So Jake Brakes are popular with drivers because they save brake pads, and unpopular with others because of the noise.
To add on to this in response to the excellent top post: How does engine/jake braking differ from simply downshifting to brake?
Not a thing but a maneuver. Downshifting to reduce speed or acceleration down a hill is engine breaking.
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