Imagine the amount of brake pressure required to stop a 4,000-pound vehicle. Should be a lot, right? Now imagine trying to stop that car on your own. Sound impossible? Well, that's exactly how every car works! All you need to do is press the brake pedal - and your car will slow down. But here's the question - how can you generate all the braking power with just your feet? This is where the brake booster comes into play. But what is a brake booster? In this article, we'll cover everything you need to know about brake boosters.
We'll cover what they are, how they work, brake booster problems and symptoms, and even show you the easiest way to fix them!
What is a brake booster and what does it do?
A brake booster is a device that amplifies the force applied to the brake pedal as it is transmitted to the master cylinder. Braking systems with them are often referred to as "dynamic brakes".
Almost all cars with hydraulic brakes use brake boosters - you won't see them on vehicles that use a pressurized air system as their primary brake circuit.
Here's how a brake booster can be an important part of your braking system:
· When you depress the brake pedal, your foot applies approximately 70 pounds of force to the brake pedal.
· This force is amplified on the master cylinder through the brake booster (typically 200-300 lbf more)
· The master cylinder then converts this force into hydraulic
· Hydraulic brake fluid transmits pressure through brake lines
· The transmitted hydraulic pressure engages the caliper (in disc brakes)
or the wheel cylinder (in drum brakes)
· Brake pads (on brake calipers) or brake shoes (on wheel cylinders) then use this pressure to create friction and slow the wheel to a stop
What if modern cars don't have boosters?
Without the brake booster, we had to press harder than usual to get the brake system to engage. The stopping distance will increase and emergency braking may not be as effective!
What else are brake boosters known as?
Since brake boosters have been around for a while, they have other names like:
· Power brake booster
· Power brakes system
· Brake vacuum servo
· Brake power booster
· Vacuum booster
The 3 Types Of Brake Boosters
There are three types of brake boosters.
Each brake booster is typically mounted on the firewall in the engine compartment. You’ll find it attached between the brake pedal and the master cylinder:
1. Vacuum Brake Booster
The vacuum brake booster is the most commonly used type.
It utilizes the engine vacuum in naturally-aspirated petrol engines to amplify the pressure applied on the brake pedal.
2. Vacuum Pump
Some road vehicles use a vacuum pump instead of the engine intake manifold.
These include:
- Cars with turbo-charged engines
- Vehicles with diesel engines
- Electric vehicles
- Hybrid vehicles
Vacuum pumps can be driven mechanically (from the engine) or via an electric motor (electric brake booster). The vacuum pump is also used in high altitude locations where naturally-aspirated vehicles can’t produce enough vacuum for the brake booster.
3. Hydro-Boost Power Brake
This type of brake booster uses direct hydraulic pressure generated by the power steering pump instead of relying on vacuum pressure.
9 Symptoms Of A Bad Brake Booster
You now know how brake boosters work.
But what happens when something goes wrong?
Here are some of the symptoms of a faulty brake booster.
1. Stiff Brake Pedal Action
A hard brake pedal is often a strong indicator of brake booster failure. A failing brake booster loses the ability to amplify the force from your foot, which translates to you having to use more effort when pressing the brake pedal.
This lowered force on the master cylinder reduces hydraulic pressure in the brake fluid, making it harder to brake.
2. Increased Braking Distance
If you’ve observed that your car no longer stops as quickly as it used to, you could be having brake booster problems.
3. High Brake Pedal Position
Here, the brake pedal might travel less than usual (meaning it’s “high”), or it may take extra time to return to its original position after you let go.
Either of these conditions can happen because of an imbalance in the vacuum chambers of a failing vacuum brake booster.
4. Hissing Noise
Notice a hissing noise when you apply the brakes?
That could be the vacuum booster leaking through the diaphragm or housing, or it could
possibly be a leak in the vacuum hose.
5. Compromised Engine Function
Here’s another potential symptom caused by a vacuum leak.
Let’s say there’s a hole in the diaphragm or a malfunctioning vacuum check valve that draws air into your system.
This air may affect the fuel mix in the engine.
Improper fuel mix affects the correct measure of gas, reducing its cooling action, and increasing the friction and temperature of your engine parts. This can lead to pre-ignition, where the fuel ignites before the spark plug fires.
Pre-ignition can also lead to piston damage or a burnt valve that will require expensive repairs.
6. Warning Lights Come On
If your vehicle comes with an electronic brake booster, the assembly’s failure can affect the anti-lock braking system (ABS). As a result, your brake warning lights, like the ABS, stability control, or traction control lights, will start to glow.
7. Fluid Leakage
Fluid leaks can indicate a whole bunch of different problems in your car.
If your vehicle uses hydraulic boosters and it’s leaking power steering fluid, there is a strong chance your hydro-boost assembly will soon fail too.
Electronic brake boosters that are housed with the master cylinder can also develop leaks that can compromise their performance.
8. Overheated Hydro-Booster
Sometimes, the fluid temperature in your hydro-booster can shoot up due to environmental conditions. This temperature jump can damage the seals and the spool valve in your hydro-booster – compromising your brake performance.
9. Failing Power Steering
Hydraulic boosters are powered by the power steering pump.
If the power steering fails, the booster will typically fail at the same time.
A Simple Way To Test Your Brake Booster
A lot of these symptoms can be hard to spot since they involve various inner components of your car. But there’s an easier way to check your brake booster — especially if your car uses a regular vacuum booster.
The brake booster design allows it to hold enough vacuum to let you engage the brakes once or twice without the engine running. This helps you stop the vehicle in case of engine failure.
Here’s how you can test your vacuum booster:
- With the engine off, pump the brakes several times.
- Then, press the brake pedal lightly while turning on the ignition.
- The brake pedal should give a bit, then become firm.
- If it becomes stiff or there’s no noticeable change, the brake booster has likely failed.
If you suspect a problem with the brake booster, you should look for a mobile mechanic to help you out. It’s simply far too dangerous to drive to a repair shop without full brake function.
Final Thoughts
Your brake booster is one of the most integral components of your car’s braking system.
That’s why it’s always a good idea to make sure your brake booster is in good shape. Stick to a regular maintenance schedule so you can stay safe on the road.