Blog Car Care Advice What Causes a Hard Brake Pedal? (Diagnosis & Fixes)
Car Care Advice

What Causes a Hard Brake Pedal? (Diagnosis & Fixes)

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Does your vehicle need extra pedal effort to slow down?
Well, you may have a hard brake pedal. A hard brake pedal makes driving a tricky endeavor and especially when stopping at a red light or turning a corner.

But what causes a stiff brake pedal in the first place?

We’ve got you covered.
In this article, we’ll describe how your brake pedal should feel, and investigate the root causes of a hard brake pedal. We’ll also explore some handy methods to diagnose a hard brake pedal.

This Article Contains:

Let’s begin. 

How the Brake Pedal Should Feel Under Your Feet

It’s hard to gauge the sensitivity of your brake pedal. The brake pedal shouldn’t feel too soft or too hard. It just needs to feel firm. 

How can you tell the difference?

A normal-functioning brake pedal feels firm when you attempt to slow down your vehicle.
The harder you press down on it, the tighter it feels without applying extra pedal effort.

To understand more, let’s see what’s going on when you press that pedal and how brake boosters aid in braking:

The brake system on modern vehicles are vacuum assisted via a brake booster. A vacuum diaphragm enhances the pedal effort that you apply to the brake pedal, which makes braking effortless, and gives you more control.

The vacuum source is sealed off when pressure is applied to the brake pedal. This closure allows atmospheric pressure to enter one side of the booster’s vacuum diaphragm — multiplying the amount of force applied to the master cylinder piston. The master cylinder piston applies the brakes. 

You need the extra force, because it’s not easy to stop a moving 4,000 pound car with your foot.

When you take your foot off the pedal, vacuum returns to both sides of the booster’s diaphragm, and the master cylinder piston returns to its original placement.

Now that we’ve covered how brakes should typically feel, let’s explore the potential causes of a hard brake pedal. 

9 Possible Causes for a Hard Brake Pedal

The braking system has many crucial components, such as the brake switch, pedal, and parking brake, which makes spotting root issues difficult.

Here are nine potential causes for a stiff brake pedal:

1. Bad Brake Booster

A bad brake booster may cause the brake system to malfunction and lead to a hard brake pedal.


Most vacuum assisted power brakes rely on the engine vacuum. Through a vacuum hose, the vacuum brake booster connects to the engine’s intake manifold — allowing the process of drawing air into the engine to also draw air from the front chamber of the brake booster via an air intake valve.

However, the vacuum diaphragm in the booster may sometimes tear. 
When that happens, the vacuum brake booster can’t maintain vacuum pressure. This inability to maintain the vacuum pressure leads to a hard pedal.

2. Faulty Check Valve

The brake booster of a vehicle has a check valve. This one-way valve prevents the loss of vacuum in the brake booster. The check valve also protects the brake line from developing air bubbles which can seriously hamper your braking. 

Over time, the valve may become faulty, allowing atmospheric pressure in — and the brake booster won’t be able to maintain the vacuum it needs to function.

This loss of vacuum affects the master cylinder, which can’t send sufficient hydraulic pressure through the brake fluid to the brake caliper or wheel cylinder, leading to stiff brake pedal action.

3. Faulty Vacuum Pump or Power Steering Pump

Some vehicle brake boosters, such as the vacuum pump booster or hydraulic brake booster, don’t rely on engine vacuum. These brake boosters use an electrical-driven pump or a power steering pump to perform their function respectively.  

If your vehicle has one of these brake boosters, and you’re experiencing a stiff brake pedal, some common issues could be a failing electric pump, or low power steering fluid.

A good indicator of a faulty vacuum pump booster is if your brake light flickers whenever you use your brake pedal.

4. Leaking Vacuum Hose

A vacuum hose (also known as the vacuum line or brake hose) links the power brake booster to the engine. It assists in drawing air into the engine to create a vacuum. 

The vacuum hose may rot or crack at its connecting points, which leads to a vacuum leak. The vacuum leak, in turn, can cause a hard brake pedal. A good indication of a leaking brake hose is if you hear a hissing sound when you apply your brakes.

5. Seized Brake Caliper

Brake calipers are a crucial component of your braking system. The brake caliper pushes the brake pad against the rotor when you apply your brakes. 

Sometimes, brake calipers can become stuck, preventing them from correctly pushing the brake pad. Stuck brake calipers can’t deliver hydraulic pressure through the brake system smoothly, leading to hard brakes.

6. Stuck Brake Fluid Residue 

When the brake system is exposed to air, the brake fluid absorbs moisture. The presence of water leads to sludge buildup that limits the flow of the brake fluid. This limitation leads to a hard brake pedal.

7. Incorrect Brake Pedal Ratio

The brake pedal ratio is the relationship between the pedal’s pivot points and the length of the brake pedal. 

An incorrect brake pedal ratio can severely impact how your brake booster and master cylinder piston work, possibly decreasing brake pressure. This disruption can lead to hard brakes.

8. Damaged Master Cylinder

The master cylinder drives the brake pressure generated by the brake pedal to the front wheel and rear wheel. This pressure is transmitted via the hydraulic fluid traveling through the brake line.

If your master cylinder is damaged or has passed its lifespan, your brakes will lock up, and you may experience a hard brake whenever you try to slow down.

9. Incorrectly Adjusted Rear Drum Brakes

As time passes, your car’s rear brakes may deteriorate. The distance between the drum brakes and the shoes will become uncalibrated as they worsen. This incorrect calibration will make it difficult for you to apply the necessary pressure to the brake, leading to a hard brake.

While knowing the various causes of a hard brake is helpful, it’s essential to understand how to diagnose them and remedy the issue.

How to Diagnose a Hard Brake Pedal?

A hard pedal can pose quite a dilemma, especially on a busy highway that requires you to brake often. Your brake switch light can flicker inconsistently, causing problems for other drivers.

Here are five ways to diagnose a hard brake pedal:

1. Check the Brake Booster

A bad power brake booster is a common cause of a hard brake pedal. As such, it should be your first consideration when diagnosing a hard brake pedal. 

Here’s how to manually check if your brake booster is problematic:

The brake pedal doesn’t move because there isn’t enough vacuum pressure within the brake booster.

How to fix: You may need a new brake booster. Get a mechanic to confirm the issue.

2. Examine the Booster Check Valve

The check valve is a one-way valve that allows air to flow toward the engine and prevents air from entering the brake booster. The check valve holds vacuum pressure within the brake booster when you start your engine. 

A good indication of a faulty check valve is if air continues to travel through the valve and out through the side, where it connects to the brake booster.

How to fix: The check valve is a simple but crucial part of your booster’s function. If your check valve is faulty, you should get it replaced.

3. Check the Brake Fluid

As previously mentioned, brake fluid absorbs water which causes the sludge to build up within the brake line, leading to a hard brake pedal.

If you suspect the brake fluid is the root cause of your issue, inspect the color and appearance of the brake fluid. Locate the brake fluid reservoir and check its contents using a flat screwdriver.  

Usually, brake fluid appears clear with an amber tint. If it seems thick and dark, then the brake fluid is contaminated.

How to fix: You’ll need a brake fluid flush to replace the contaminated fluid. 

4. Inspect Vacuum Hose

The main purpose of a vacuum hose is to connect the engine to the brake booster, to transport the vacuum pressure. 

The brake hose experiences wear and tear over time, and cannot perform its function. In rare cases, the wrong size or type of vacuum line was attached, derailing the entire braking system.

How to fix: Get the worn vacuum hose replaced or have the correct type of vacuum hose installed.

5. Check the Brake Pedal Ratio

Although it’s uncommon for the brake pedal ratio to be the leading cause of a hard pedal, it’s possible. It’s more likely to happen if you’ve converted your brake pedal from the OEM setup.

If your vehicle has the incorrect brake pedal ratio, the brake pressure from the pedal will not reach the brake booster, making braking much more difficult. 

Diagnosing an incorrect brake pedal ratio requires inspecting the pedal ratio and pivot points. Typically, a standard brake pedal has a 4:1 ratio. 

How to fix: Adjust the brake pedal ratio. This task isn’t simple, so it’s best to seek professional help.

Closing Thoughts

Several common causes could lead to a hard brake pedal. The root issues vary from a bad brake booster to contaminated brake fluid. The easiest way to diagnose and resolve issues with your brake pedal is to contact a mechanic.

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