Brake System: Diagnosing a Brake Pedal

Introducing Brakes

When driving on a freeway, the need to slow down or stop your car may come up. This can be as a result of an obstacle before you or can be instigated by another situation. When this need arises, the brakes are applied to bring the vehicle to a stop. As faster cars become a regular invention, more efficient brake systems are needed to ensure the safety of the driver and passengers on board.

Hard brake pedals can affect this efficiency negatively, therefore, this article aims at addressing how to diagnose and correct hard brake pedals.

brake pedal

The brake system and how it works

Automobile manufacturers now implement brakes on all four wheels of modern cars and a hydraulic system is in place to operate it. Anytime brake is applied to a moving vehicle its weight is thrown forward onto the front wheels and this makes the front brakes more important in stopping a vehicle.

As a result of this, most car manufacturers use a disk brake at the front wheels because it is more efficient and drum brakes at the rear wheels. However, for most expensive or high-performance modern cars, disk brakes are used on all four wheels. while, on older and slower cars, all drum brakes are used.

To brake a car, the master cylinder depresses once the brake pedal is pressed and supplies fluids to the slave cylinders until they are full. This in turn pushes the pistons out to apply the brakes. Barring any leaks, the fluid is distributed evenly across the system and effective braking takes place.

In some cases where braking is sudden and hard, too much weight may be lifted off the rear wheel. This can, therefore, cause an absolute grip on the wheels resulting in a skid which could be dangerous in some cases. This is the reason for making the rear brakes less powerful than the front.

Recently some advanced cars may even have complex anti-lock systems that sense how the car is decelerating and whether any wheels are locking, such systems apply and release the brakes in rapid succession to stop them from locking. Watch the video below to see how brakes work.

Reasons for flat or hard brake pedals

Bad brake fluids

Over time, as you continuously drive your car, the brake fluid degrades. This is because the fluid picks up dirt, moisture, and debris from your braking system as it runs through it. This can be identified from the color of the brake fluid and its texture as well. It will turn from a clear liquid that usually has a yellow or amber shade to a darker brown color and will become thicker in texture.

In some cases, it feels more like sludge than a liquid. As this happens, the fluid loses its good qualities and adds more resistance to your brakes instead of allowing them to operate smoothly. In a case where the fluid becomes too sludgy, it builds more resistance and makes the pedal difficult to press down.

Learn more about brake fluids here.

Good Vs Bad Brake Oil

Air in brake lines

The transmission of every brake system must be airtight and devoid of any air in the hydraulic fluid present. However, air can find its way into the system either when repairs are being carried out or while fluid is being added. It can as well find its way in as your car operates normally.

Air is one of the main reasons brake pedals become soft because it does not provide any force that helps the brakes stop the wheels. When this occurs, there are gaps in the brake fluid and the brake pedal is pushed to its limit while braking due to the lack of force present in the line.

Worn brake pads

Brake pads create friction on the brake disks, this, in turn, controls the way the vehicle slows down by reducing its speed. However, the more brake pads are in use, the more they wear down due to aging. Most times grinding sounds accompany wear and this makes them stiff, resulting in a hard brake.

New Vs Worn Brake Pads

Leaking brake lines

Insufficient fluid present in the brake system due to leakage is another common reason why your brake goes soft and its pedal flattens. A rupture in one of the brake lines is one of the most common causes of this.

There are many things that could cause a leak in the brake lines.  Two major causes include aging driving through very rough terrains. Due to low brake fluid, enough pressure is not exerted when the brake pedal is pressed and the pedal flattens as a result of this.

Leaking Brake Line

Absence of vacuum pressure

The absence of vacuum pressure is one of the major common causes of a hard brake pedal. This should, therefore, be the first thing to look out for when you encounter a hard pedal.

The vacuum pressure helps with the force exerted when the brake pedal is pressed. This is for better convenience and control while braking. The vacuum pressure will be lost if the diaphragm connecting the hose or valve develops a fault. In the absence of vacuum pressure, braking becomes a chore as a hard pedal is developed.

Caliper problems

It is the job of the caliper to move the brake pads and they need to operate smoothly to engage and disengage the brake pads to either stop the vehicle or let it go. As a result of dust and dirt, these calipers or their screws get stuck and in some cases break.

Signs of a bad caliper tend to show while steering. It is identified by a  slight smell of burning and a feeling of drag. These can also affect your brake pedal because a stuck caliper can't release and position its pad. This is felt by the driver on the brake pedal as it becomes too stiff to move.

Brake caliper problems

Bad brake booster

Another reason you might be experiencing the brake pedal going down to the floor is a bad brake booster. Whenever you step on the brake, the brake booster comes on and powers the brake system to stop the vehicle.

However, in a situation where the brake booster is falling, the brakes take time to engage it might not engage at all when the pedal is pushed resulting in a soft pedal. Driving in populated areas which require constant vigilance and the use of brakes affects or reduces the lifespan of the booster. This is natural the wear and tear of any component.

brake booster

Bad master cylinder

A master cylinder failure is another main reason your brake pedal can go soft. A master cylinder failure is mainly a result of wear and age. Since the master cylinder’s main job is to supply brake fluid to the brake lines, a failure means the lines do not receive brake fluids resulting in flattening of the brake pedal. To learn more about the master cylinder, click here.

Bad master cylinder

Simple ways to diagnose hard pedals

Test the functionality of the vacuum booster

In smaller passenger vehicles and light trucks, an intake manifold vacuum is what operates the power brake boosters or the conventional brake assist. When they develop hard pedal problems, it should, therefore, be the first thing to be tested. This is done by turning the engine OFF and separating the check valve from the power booster.

To remove the check valve easily, it should first be lubricated with a substance like aerosol silicone. There should be a vacuum present in the booster. If there isn’t, however,  the front and rear pushrods should be checked for leaks. If there aren’t leaks the engine should be turned ON and the valve grommet checked for leaks.

As these inspections are going on, the brakes should be pressed and released. Once a leak is detected, carry out repairs as soon as possible. Next, check out the vacuum booster’s interior. If it is full of brake fluid, it means there are leaks from the master cylinder.

This, therefore, means that you should replace the booster and the master cylinder should be replaced. Sometimes the intake manifold vacuum becomes low, and this could affect the engine performance in different ways like:

  • having a clogged-up exhaust
  • slowed valve timing or
  • a major vacuum leak

After all of these are done, turn OFF the vehicle and step on the brake it should feel hard and stiff.  Turn ON the vehicle again. This time, the brake pedal should immediately feel soft and go down if the vacuum booster is functional. A vacuum booster on another hand could pass all these tests and still be faulty from the internal vacuum metering system. This can’t be diagnosed by a test so the brake booster should be replaced.

Inspect the brake fluid

Sometimes the cause of a hard brake pedal could be simple, obvious, and overlooked which is the brake fluid itself. After a long time of usage, the brake fluid can pick up dirt particles as it flows along the transmission lines, and also brake fluid has the ability to absorb water.

These can accumulate over time and form sludge and due to sludge having more resistance they don’t flow well in pipes and hoses and on some occasions get stuck. Good and clean brake fluid should be clear and have a little brownish tint to it.

To check if the brake fluid has gone bad, open the fluid reservoir then a slim flat metal or flat screwdriver should be used to gently scrape some fluid from the surface of the reservoir and inspect it.

If the fluid is clear and still looks like what a good brake fluid looks like it is fine and isn’t the cause of the hard pedal, but if it looks darker and sludgy then the fluid is bad and needs to be changed. For a detailed guide on how to change your brake fluid, click here.

Inspect the brake fluid

Check the hydraulic booster

The hydraulic power steering pump provides brake assist in some cases as in the case of many light trucks. So a failure or wear down of the power steering pump could result in a hard brake. This could be tested by turning the steering wheel to lock. If the steering feels unusual, you check the power steering fluid level then its viscosity and color.

A change in color or viscosity might indicate that the engine oil or brake fluid has been introduced into the pump reservoir. If all is good, the next thing is to pump the brake pedal by pushing it repeatedly.

This drains the hydraulic assist. After this, press down on the pedal and start the engine. You should feel a mild kick or counter push from the pedal. If this doesn’t happen, the hydraulic assist unit is bad or worn out.

Quality and size of vacuum hose

A faulty brake valve can disrupt the entire brake system as well as a wrong and faulty hose. The vacuum hose is responsible for getting the vacuum pressure from the engine to the booster. It, therefore, runs from the booster to the engine. There are two main problems that can be vacuum hose issues.

One is, having a bad quality hose which wears down quickly hence, making it worse in performance. The second is having the wrong size attached. Some people do not know this, but vacuum hose comes in different sizes and are of different qualities.

Generally, the size of a given hose is encoded in the hose ID which can be found on the body of the hose, towards the middle of its surface.

On average, a vacuum hose that connects to a power brake booster has a size ID of 11/32”. This ID is not to be confused with the fuel line of a car, which people tend to assume is roughly the sizing guide for a vacuum hose. The size ID of a fuel line differs because it is roughly 3/8”. There is no particular way of diagnosing a bad vacuum hose except by visually checking the hose or its size ID.


For the safety and efficient function of vehicles, the brake system needs to function without any type of hitch. Hard and soft pedals could be encountered but do not panic.

Once a problem is detected /diagnosed, book an appointment with an auto mechanic immediately. Some diagnoses can only be done by professional auto mechanics. Therefore, if you can’t figure out what is wrong, call a mechanic ASAP. Drive safe!

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