What Is A Brake Booster


Brake boosters have been around for decades. They were originally invented in 1927 and are one of the many reasons that we don’t get a leg workout every time we want to stop our cars.

What’s a brake booster? A brake booster is a device that decreases the amount of human effort needed to slow and stop a vehicle.


The booster uses vacuum from the engine or from a dedicated vacuum pump to allow atmospheric pressure to assist with pushing a piston that applies hydraulic pressure to the brakes.

Start and stop traffic would be a nightmare without this. While a physical cutout of a brake booster would make it look more complicated than it is, the overall concept is surprisingly simple for a device that makes our lives remarkably easier. We (almost) literally stop our vehicles with air!

What is it? How does it work?

The internal workings of a brake booster is mainly nothing. Really.

Imagine a container with two chambers, number one and number two. Both of these chambers have nothing in them – just a vacuum. Between these chambers is a wall that moves if something pushes it.

If we let air into chamber one, the normal, atmospheric pressure will push the wall towards the vacuum in chamber two. Congratulations, you’ve just graduated with your simplified degree in brake boosters.

The reason we use brake boosters is to allow the pressure of the air around us to take some of the strenuous load of braking a 3,000 pound car off of our legs.

Remember that when the brake pads of any vehicle contact the rotors to stop the vehicle from moving, they have to press hard and long enough for friction to remove enough of that kinetic energy to avoid hitting whatever is in front of you.

If you’re using your own leg strength, you may notice two notable things:

  • Stopping your car is really hard.
  • If you have pedestrians in front of you, their life depends on your ability to stop a 3,000 pound vehicle that, as we mentioned in the first point, is really hard to stop. Good luck.

Let’s also note the fact that some vehicles are a lot heavier than that. These devices are the reason that a 110 pound teenager can easily slow and stop their parent’s 6,000 pound pickup truck after driving at interstate speeds. Is this brake booster idea making sense yet?

One thing we didn’t mention before your graduation is that the moving wall between those two chambers has a rod connected to your master cylinder. When that rod moves, the piston in your master cylinder moves with it to create the hydraulic pressure that moves your brake pads.

This means that the air you let into the brake booster is doing a lot of the work for you, so you can focus one more important things, like driving safely.

The second chamber – the one that we don’t allow air into – has its vacuum created by the intake of your engine. This is a clever design, because it doesn’t require adding any additional parts to your vehicle to make the brakes work.

However, there are vehicles where a vacuum pump may be used anyway. Some hybrid and electric vehicles might have a dedicated vacuum pump if they use this design.

Remember that brake boosters are simply that – boosters. They don’t do all of the work for you. They just make the job a lot easier.

Different Types Of Brake Boosters

As with anything in this world, there are multiple variations depending on what’s more convenient. Some are better than others in certain situations, but none are 100% suited for every application. In this case, there are three main types:

  • Vacuum Boosters – You have your degree in this already: 14.696 PSI of atmospheric pressure pushes a diaphragm with a rod connected to your master cylinder.
  • Hydro-Boost – This version uses hydraulic pressure from the power steering pump.You’ll find this mainly on vehicles where the engine doesn’t create enough vacuum for a typical vacuum booster – diesel vehicles, for example. Alternatively, a manufacturer might choose to use a vacuum pump instead.
  • Electro-Hydraulic – These are the only version discussed on this article that don’t directly use the pressure of the brake pedal to apply pressure to the brakes themselves. Instead, a sensor connected to the brake pedal measures the distance that the driver moves the pedal.Pumps elsewhere in the vehicle use this and other relevant information (speed, potential emergency situations, etc.) to pump pressurized hydraulic fluid to the car’s brakes – even individual brakes, if necessary.

This is more likely to be found in electric vehicles if a manufacturer chooses not to use a vacuum pump.

Possible Issues

If you have any experience with any vehicle, you probably saw this coming. Everything has issues eventually, and brake boosters aren’t the exception.

Even if you don’t know how to fix the issue you’re having, it does give some piece of mind to understand what might be the cause. Your brake booster might be failing if:

  • It takes more effort than usual to press your brake pedal.
  • Your engine stalls or the RPM goes down when you press the brakes.
  • Your stopping distance is suddenly much longer.
  • (Worst case scenario!) Your brakes no longer work.

There are guides elsewhere that detail the process for diagnosing and fixing a faulty brake booster. The advice from this article is simply to stop driving your car and get it fixed by a trusted mechanic.

If you don’t know what you’re doing, it’s best to let a professional work on your brakes, as any mistakes will be unforgiving for everyone involved.

Brake Booster “Delete”

There is a small subsection of drivers who find value in removing their brake booster. This is sometimes called a “Brake Booster Delete”, and is generally done for visual or performance reasons while racing.

With a brake booster, you don’t have to press the pedal very far before finding that point where the wheels lock. This is especially true on surfaces with less friction, like gravel or snow.

Without the brake booster, the driver has more “space”, or a larger working range of the brake pedal before the wheels lock. This is often better for racing purposes. Some drivers may also remove the booster to make their car look nicer.

Hopefully, this doesn’t need to be said, but we’ll say it anyway: This is a bad idea.

Did you catch that? We’ll say it again, just to make sure:

Performing unnecessary procedures to downgrade the braking system for a heavy piece of machinery travelling at 50+ miles per hour is a bad idea.

We don’t care if it looks nice. We don’t care about your race. Other people on the road (especially pedestrians) want you to be able to stop your car with as much ease as possible.

Brake boosters were invented decades ago, and they’ve stayed in cars for this long for obvious reasons – safety being one of them. While a car is still “drivable” without the brake booster, it’s not easily stoppable, and that can turn a bad situation into a serious one.

If something is wrong with your brakes – the things you use to avoid running people over and/or causing thousands of dollars’ worth of damage to other people’s property – get it fixed. If you remove parts of your braking system intentionally, stop driving.

Stay safe!

Arwood

I'm Arwood, but the grandkids call me Big Papa. After retiring from teaching automotive classes for 30+ years I decided to create a blog about all the questions I used to get about brakes!

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