For your vehicle's braking system to perform effectively and smoothly, it needs a brake booster that's in good condition. The brake booster is a critical component, typically found between the brake pedal and the master cylinder. It multiplies the force you apply to the pedal, making it easier to slow down or stop your vehicle. To find out more about brake boosters and when to replace yours, keep reading.

What Brake Boosters Do

The brake booster is a vital part of your vehicle's braking system. When you press down on the brake pedal, the booster uses a power source (most commonly engine vacuum, but sometimes hydraulic pressure from the power steering system) to amplify the force exerted by your foot. This amplified force is then transmitted to the brake master cylinder, which converts it into hydraulic pressure to activate the brakes. Basically, it reduces the physical effort required from the driver to achieve effective braking.

Types of Brake Boosters

Vacuum Brake Boosters

Vacuum brake boosters are the most common type. They use the vacuum generated by the engine (or a separate vacuum pump on some diesel or turbocharged engines) to create a pressure differential across a diaphragm. This differential assists in pushing the master cylinder pushrod when the brake pedal is applied.

Hydraulic Brake Boosters (Hydro-Boost)

Hydraulic brake boosters, often called "Hydro-Boost" systems, use hydraulic pressure generated by the vehicle's power steering pump. These are usually found on diesel vehicles or vehicles with limited engine vacuum. They provide a powerful and consistent assist.

Electro-Hydraulic Brake Boosters

Some modern vehicles, especially hybrids and electric vehicles, may use electro-hydraulic brake boosters. These systems use an electric motor to generate hydraulic pressure for brake assist, often integrated with regenerative braking systems.

Brake Booster Components

While you'll buy a brake booster as a complete unit, understanding a few of its key internal parts can help you appreciate how it works and why failures occur.

For Vacuum Boosters:

・Diaphragm(s): Think of this as the heart of a vacuum booster. It's a large, flexible rubber disc (sometimes two for extra power) that divides the booster's internal chamber. When the engine vacuum pulls air from one side, pressing the brake pedal allows atmospheric pressure on the other side, creating the force that assists your braking.
・Control Valve / Air Valve: This intricate valve is connected to your brake pedal. When you press down, it skillfully allows outside air into one side of the diaphragm to create the assist. When you let off the pedal, it seals off that air and re-establishes vacuum, making the system ready for the next stop.
・Check Valve: This small but vital valve, usually where the vacuum hose connects, acts like a one-way door for air. It lets the engine draw air out to create a vacuum but prevents air from rushing back in.

For Hydraulic (Hydro-Boost) Boosters:

・Spool Valve & Piston: These are the workhorses in a hydro-boost system. The spool valve, reacting to your pedal input, precisely directs high-pressure power steering fluid to a piston. This piston then generates the powerful force that assists your braking.
・Accumulator: This is a safety feature, often a small nitrogen-charged chamber. It stores a reserve of pressurized hydraulic fluid. If your engine (and thus power steering pump) suddenly stops, the accumulator provides enough pressure for a few assisted brake applications, giving you a chance to stop safely.

Common to Most Boosters:

・Pushrods: An input pushrod connects to the brake pedal, and an output pushrod presses on the master cylinder.
・Return Spring(s): These help the brake pedal and internal booster components return to their resting position quickly when you take your foot off the brake.

Symptoms of a Failing Brake Booster

Brake Pedal is Hard to Press

A significant increase in the effort needed to press the brake pedal is a primary symptom. This indicates a loss of power assist, often due to a vacuum leak (in vacuum boosters) or a problem with the hydraulic supply (in hydro-boost systems).

Braking Distance is Noticeably Longer

If the booster isn't providing adequate assistance, you'll need to press the pedal much harder, and it may take longer to stop the vehicle than usual, increasing braking distances.

Pedal Is Higher or Stiffer than Usual

A failing booster, particularly one with an internal vacuum leak or control valve issue, might cause the brake pedal to feel unusually high or not return smoothly.

Stalling Engine or Hissing Sound (Mainly Vacuum Boosters)

A hissing sound when the brake pedal is pressed or released often indicates a leak in the booster's diaphragm or vacuum hose. A significant vacuum leak can also affect engine idling, sometimes causing the engine to stumble or stall.

Fluid Leaks (Primarily Hydro-Boost)

For hydraulic boosters, leaks of power steering fluid around the booster unit can indicate seal failure within the booster.

Brake Warning Light on Dashboard

While many issues can trigger the brake warning light, a failing booster that impacts overall brake system performance or is monitored by vehicle sensors could cause the light to illuminate. Always get an inspection for an accurate diagnosis.

How to Choose the Right Brake Booster

Aftermarket or OEM

Original Equipment Manufacturer (OEM) brake boosters are those made by either the car brand itself or their authorized manufacturers, whereas aftermarket units are made by third-party manufacturers.

We recommend investing in OEM brake boosters to return your vehicle to its original level of performance and safety. Due to potentially more stringent manufacturing and testing standards, you may get more reliable service from an OEM replacement. Also, ensure aftermarket units meet all safety and compatibility standards for your vehicle.

Vehicle Compatibility and Type

To guarantee a proper fit and function, ensure that you're getting a brake booster specific to your vehicle's make, model, and year. Boosters differ in size, mounting configuration, pushrod length, and type (vacuum, hydraulic). Using the wrong type or an incompatible unit can lead to improper brake function or installation issues.

Installation and Considerations

Replacing a brake booster is a fairly involved job that requires mechanical know-how. Generally, the process includes:

1. Disconnecting the master cylinder, brake pedal linkage, and vacuum or hydraulic lines from the old booster.
2. Removing the old booster from its mounting on the vehicle's firewall.
3. Mounting the new booster and carefully reconnecting all lines, linkages, and the master cylinder.
4. Making sure all connections are secure and, for hydraulic systems, potentially bleeding the system to remove air.
5. Finally, the brakes need to be tested.

Given the complexity and the critical safety role of the braking system, it's often best to have a professional mechanic handle brake booster replacement.

Where to Buy Quality New & Used Brake Boosters

Brand-new brake boosters can be found at various trusted auto parts dealers, dealerships, and online retailers. For used brake boosters that are in excellent condition and at great prices, shop here with BE FORWARD Auto Parts.