A brake booster is often referred to as a “brake servo” or “vacuum booster”. A brake booster increases the force applied to the master cylinder when the brake pedal is depressed.
We’ll go over what brake boosters are, how they work, the different types that are available, how to tell if yours is failing, and ways to cut costs on your auto insurance in this post.
Different Types of Brake Boosters
There are a few different types of brake boosters in use today:
- Vacuum Brake Booster Systems
- Hydro-Boost Brake Booster Systems
- Electro-Hydraulic Brake Booster Systems
Read on for an explanation of each system type.
Vacuum Brake Booster
A vacuum-type booster is the most common type found in passenger cars. A vacuum booster, which is installed on the firewall between the brake pedal and the brake master cylinder, is a common feature of gasoline-powered vehicles. A flexible diaphragm separates the booster’s two sides, which are both chambers made of metal.
Vacuum boosters typically have a diameter of 6 to 8 inches and a thickness of 3 to 4 inches. Engine vacuum is supplied to both sides of the diaphragm until the brake pedal is pushed. The pedal side of the chamber experiences atmospheric pressure as a result of a metal rod pushing a valve up against the diaphragm as the pedal is depressed. With the master-cylinder side of the chamber still under vacuum, the difference in pressure creates the assistance or “boost” needed when applying the brakes.
A vacuum pump can be used to provide the vacuum required for proper booster operation in situations where engine vacuum is insufficient.
Read More: How Long Do Car Brakes Last?
Hydro-Boost
A hydro-boost brake booster is mounted on the firewall between the brake pedal and master cylinder, just like a vacuum booster. The power steering pump provides hydraulic pressure in place of engine vacuum to assist with braking.
As the brake pedal is pressed, a spool valve moves inside the housing and directs fluid pressure into a chamber. When the brakes are applied, a piston advances and provides a boost due to the force of the fluid in the chamber. In the event that the pressure for power steering is lost, an accumulator stores the pressure.
Also Read: How Often To Flush Brake Fluid
When using supercharged or turbocharged engines, or when diesel engines are not an option, hydro-boost is used to supplement the engine vacuum.
Electro-Hydraulic
Electro-hydraulic boost is a newer type of braking assistance deployed on hybrid and electric vehicles. Referred to as “brake-by-wire”, there is no direct connection between the brake pedal and the brake system. Both electrical and hydraulic components make up the system. Sensors measure the amount of pressure applied to the brake pedal and send these signals to an electronic control unit (ECU).
An electro-hydraulic brake system combines the functionality of anti-lock braking and stability control into a single unit, determining how much brake pressure is required at each wheel using inputs from a number of sensors. Regenerative braking on electric vehicles is also integrated into the system. When the electric motor reverses to slow the car down and charge the batteries, this happens. The amount of input from the brake pedal is used to calculate whether the vehicle needs additional hydraulic help to stop.
While vacuum and hydro-boost brake boosters have been common for decades, they may gradually be phased out in favor of electro-hydraulic systems for more precise control of braking and integration with vehicle safety systems.
How Does a Vacuum Brake Booster Work?
The most common form of boosting a car’s braking capability works via a vacuum feed from the car’s engine. Let’s take a quick look at how that appears.
Firstly, the brake booster attaches to the master cylinder, which bolts up against the engine-side firewall within easy reach to the rest of the braking system, as well as the brake pedal inside the car.
The actual device is a straightforward metal chamber divided by a diaphragm, with a shaft in the center that is equipped with a series of valves and springs. When the brake pedal isn’t depressed, vacuum occupies both chambers. When pressed, a valve on the side facing the brake pedal opens, allowing atmospheric pressure (or the pressure that has built up from outside the vacuum system) to enter.
This atmospheric pressure is prevented from entering the vacuum-only side of the chamber, which is facing the master cylinder, by a one-way check valve.
In addition to pedal pressure supplied by the driver’s foot to push the shaft forward, the pressure differential between the two halves—increases braking pressure even more. This atmospheric-sided force is increased to exert more pressure on the brake master cylinder, which then forces hydraulic fluid from the system out to each brake line and then to each caliper and/or drum (but not before it reaches the ABS pump).
How Does Brake Booster Affect Performance?
The master cylinder pushrod is pushed harder by the brake booster. In many cases, it can add 200-300 lbs. of force. However, the actual force depends on:
- The size of the diaphragm
- The amount of vacuum applied
- The atmospheric pressure in the air
Without increasing the force you apply to the pedal, the additional force helps the braking system develop the high pressure that is required. This facilitates stopping and improves the driving experience.
How to Test Your Brake Booster
There is an easy way to check your brake booster if you think there may be a problem.
Brake boosters are made with enough space to hold a vacuum for one or two extra brake engagements while the engine is off. To test your brake booster, pump the brakes a few times with the engine off, and then press the pedal down as you turn the engine on.
If there is no change in the feeling of your brake or it immediately becomes stiff and hard to press, it’s a good chance there has been a brake booster failure.
You should get in touch with a mobile mechanic if you think your brake booster may be broken; you don’t want to drive around with subpar brakes! Be sure you’re hiring a certified mechanic that works with quality tools and parts since “fixing” a brake booster generally means you’ll have to replace it.
Signs of a Failing Brake Booster
A brake booster may start to malfunction for a number of reasons. One would be an increase in noise as all vacuum brake boosters make a light pump-like noise. But if it suddenly becomes louder than usual, this might be a sign that it’s about to go.
A weak braking system may also be indicated by fluid leaks near the booster/master cylinder assembly.
As well as longer brake pedal travel. If you notice that you’re applying more pressure to the brake pedal than usual and your brake rotors, brake pads, and fluid are all in good condition, with no leaks in any brake lines, it may be a sign that the brake booster, either in the booster itself or in the vacuum lines that connect to it, has a leak.
Another indication is a change in the pedal’s firmness; if the pedal is now extremely difficult to press and it takes more effort to slow down or stop from a reasonable speed, your braking system may need to be repaired, and you’ll be forced to use fully manual brakes once more.
Another indication that one or more of the booster’s components has failed is a brake pedal that returns to its unpushed position slowly or not at all.
It’s interesting to note that because the vacuum system in the booster is interconnected, a vacuum leak there can result in a poorly running engine. The possibility of a complete loss of braking force in the event of an electric brake booster failure is quite frightening. Thankfully, many modern vehicles will alert you with an ABS or check engine light, urging you or a technician to look into the problem further.
Conclusion
The brake booster is a canister that sits between your brake pedal and the master cylinder. Much like power steering helps us steer, brake boosters help us in the braking process. Some breaking systems work at high fluid pressures, this has the ability to make our brake pedals hard to use. This job is simplified by brake boosters. When you apply brake pressure, the booster adds to the force applied to the master cylinder.
FAQs
Can You Drive Without Brake Booster?
Driving while your brake booster is broken or in need of repair is extremely risky because it could eventually cause your brakes to stop working altogether.
What Happens If a Brake Booster Fails?
When a brake booster fails, it loses its capacity to increase the force generated by your foot, requiring you to exert more force to depress the brake pedal.
Why Do Cars Have Brake Boosters?
What power steering is to a car’s steering system, a brake booster is to a car’s braking system. The main goal of a brake booster is to make it possible to stop your car safely with only a small amount of pedal pressure.