How to Replace a Brake Booster (Step-by-Step)

A brake booster amplifies the force applied to the brake pedal and transfers it to the brake master cylinder. The master cylinder transforms this force into hydraulic pressure, which flows through the brake lines to the brake calipers. The calipers press the brake pads against the rotors, creating friction to stop the wheels.

If there’s a brake booster issue, braking becomes significantly harder, which makes driving unsafe and affects the vehicle’s braking system performance. 

Since brake boosters are critical for driving safety, their replacement is best left to auto repair professionals. 

Here’s how they’ll install a new brake booster:

1. The mechanic may engage the parking brake for safety (optional). Then, they’ll turn off the engine and pump the brake pedal several times until it becomes firm to relieve brake booster pressure. 
2. They’ll open the hood to find the booster between the master cylinder and firewall, with the brake fluid reservoir positioned atop the cylinder. 
3. If the brake master cylinder has an electrical connection for the brake fluid warning sensor, they’ll disconnect it. 
4. They’ll then disconnect the lines connected to the car’s brake booster:
   • For vacuum-operated boosters, they’ll remove the vacuum hose. 
   • For a hydraulic booster, they’ll place a catch pan underneath, and disconnect the pressure feed as well as return lines (hydraulic lines) using a line wrench to avoid damaging the fittings. 
5. The mechanic will unbolt the master cylinder from the brake booster by removing the retaining nuts and gently moving it aside. If space is tight, they may need to take the master cylinder out entirely. Your car will require brake bleeding after re-installation. 
6. They’ll access the area underneath the steering wheel to disconnect the brake pedal linkage from the booster’s push rod. 
7. They’ll unbolt the brake booster from the firewall by removing the mounting nuts that secure it to the brake pedal and firewall. 
8. The mechanic will carefully remove the old brake booster and inspect it for signs of brake fluid leaks, which could signal a faulty master cylinder damaging the booster. 
9. They’ll install the replacement brake booster, aligning its mounting studs with the firewall openings. 
10. They’ll reinstall the mounting nuts for the new brake booster and reconnect the brake pedal linkage. 
11. Next, the mechanic will reattach the master cylinder to the new booster, ensuring the brake line isn’t bent or damaged. 
12. They’ll reconnect the brake booster lines:
    • For vacuum boosters, they’ll reattach the vacuum hose.
    • For hydraulic boosters, they’ll reconnect the pressure and return lines. 
13. For hydraulic boosters, they’ll top off the power steering fluid (since brake boosters rely on the power steering pump for hydraulic pressure) and bleed the hydraulic system to remove air.

Finally, they’ll reconnect any electrical connections to the master cylinder and check the brake fluid reservoir. If the brake fluid level is low, they’ll top it off or add fresh fluid.

How Urgent Is a Power Brake Booster Replacement?

A faulty brake booster is dangerous and requires immediate replacement.

Brake booster failure can lead to a loss of brake system efficiency. You’ll likely have to apply more braking pressure on the brake pedal or have difficulty stopping the car. Ignoring it for too long can also affect other brake system parts, like the brake pad, pedal assembly, booster rod, etc. 

Moreover, in vacuum-operated units, a brake booster issue can cause the engine to run with insufficient vacuum pressure and fuel, affecting performance. 

So, for your vehicle’s safety, replace the faulty booster with a new one ASAP.

How Much Does a Brake Booster Replacement Cost?

The cost of a replacement brake booster depends on your vehicle’s make and model, generally ranging between $200 and $1250. This estimate covers:

• Cost of a new booster: $100 to $900 or more
• Labor cost: $100 to $200

NOTE: In addition to a bad brake booster, other repairs, such as replacing a damaged master cylinder or brake line, can increase the total replacement cost.

7 Signs You Need a Power Brake Booster Replacement

Here are some symptoms that indicate a brake booster problem:

1. Brake Pedal Issues

Faulty brake boosters can make the brake pedal harder to press and reduce resistance. The pedal may sit higher than usual, forcing you to lift your foot more and apply extra force to stop the vehicle. You might also experience increased braking distances, particularly at high speeds or on inclines.

2. Fluid Leaks

If your brake fluid level is low and there’s a puddle of amber or dark-blown fluid underneath the car, it could point to a leak. To confirm, inspect the brake system for visible leaks around the master cylinder, brake lines, calipers, or wheel cylinders. Next, insert a clean dipstick inside the brake booster vacuum check valve. If you spot any liquid residue, your car probably has a brake fluid leak.

3. Engine Noise

If your braking system is vacuum-operated, you may notice hissing sounds from the engine compartment when you use your power brakes. This is caused by a vacuum leak within the booster, resulting from a cracked engine vacuum line.

4. Warning Lights

If your brake booster is faulty, you may notice an illuminated brake or Anti-lock Braking System (ABS) light on your dashboard. In some vehicles, the Check Engine Light can also come on.

5. Performance Issues

A damaged brake booster diaphragm can cause a vacuum leak, disrupting the air-fuel mixture. In older vehicles, this may lead to reduced power, rough idling, or stalling, signaling the need for replacement.

6. Overheated Booster

High fluid temperatures in the hydraulic booster, often caused by environmental factors, can damage the seals and spool valve. This damage reduces brake performance and overall system reliability.

7. Failed Power Steering

As hydraulic boosters rely on the power steering pump to function, if the power steering system fails, the booster will fail as well. This can reduce braking power and affect the functioning of the steering column.

4 FAQs about Brake Boosters

Here are answers to some common questions you may have about car brake boosters:

1. What Are the Different Types of Power Brake Boosters?

Depending on your vehicle’s make and model, your car may have a:

• Vacuum brake booster: Common in most vehicles, it uses engine vacuum to amplify braking force but may be less effective at high altitudes or with low-vacuum engines.
• Hydraulic brake booster: This booster is used in both gasoline and diesel engines. However, it’s ideal for diesel engines, as it relies on the power steering pump pressure to deliver consistent braking performance regardless of engine vacuum.
• Electric brake booster: Designed for hybrid and electric vehicles, it uses an electric motor for precise braking without relying on vacuum or hydraulics.
• Electro-hydraulic brake booster: This hybrid system combines hydraulic pressure and electronic control. It’s often integrated with ABS and stability control.

2. How to Test a Vacuum Brake Booster?

If you’re not used to DIY repairs or handling auto parts, it’s best to let an automotive mechanic test the vacuum brake booster.

Here’s how an auto repair mechanic will go about it: 

1. Engage the parking brake, turn off the engine, and open the hood.
2. Pump the brake pedal several times to confirm there’s no vacuum in the power brake booster.
3. Depress the brake pedal while starting the engine simultaneously. If the brake pedal works, there should be a slight resistance in the pedal as the engine compartment supplies pressure to the booster.
4. Keep the engine running and pump the brake again. Repeat until the braking pressure becomes firmer, which indicates that the brake booster isn’t leaking.
5. Examine the booster check valve to verify the power brake booster pressure and disconnect the vacuum hose. If it works fine, air shouldn’t flow when vacuum pressure is applied. If it does, replace your vacuum booster.

3. Is it Safe to Drive With a Bad Brake Booster? 

No, it isn’t recommended for your vehicle’s safety. 

If your brake boosters fail, the brake pedal becomes stiff and requires extra effort to slow down the car. This can delay braking response in traffic or emergencies and increase the risk of accidents, especially at high speeds where stopping distances are much longer.

Moreover, if your brake booster fails due to a fluid leak, you should stop driving immediately and get a diagnosis. A fluid leak can cause stiff pedals and lead to complete brake failure.

4. Can You Repair a Power Brake Booster?

Yes, repairs are possible, depending on the booster type. For example, you can repair a hydraulic booster by replacing worn seals, while a vacuum booster may require a new diaphragm and seals. 

The brake booster repair process involves disassembling the unit, cleaning it, replacing damaged parts, and carefully reassembling it to prevent leaks.