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Soft Brake Pedal – What Are The Causes?

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A brake pedal that is functioning should feel firm and should provide ample stopping power. If you notice that your brake pedal is going to the floor when you press it in order to stop the car, this can be a sign that something is wrong in the banking system. A soft brake pedal describes when the brake pedal does not have firmness and can cause an unsafe situation for you and your passengers. 

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Soft Brake Pedal Causes


There are various reasons why your car could have a spongy, soft, or low brake pedal in your car. If you feel that your brakes are traveling closer to the floor when you are trying to stop your car, you need to diagnose the real issue and the cause of the soft brake pedal. If you experience any of these situations, then be sure that you have your vehicle checked and inspected right away by a local mechanic or a trusted auto body shop. 

  • Air in the Brake Lines

One of the leading causes of a soft brake pedal is air in the brake lines. The air in the line is the most common cause of the soft brake pedal since if air gets into the brake lines, it can prevent the brake fluid from flowing properly and traveling correctly. Fluid or air in the brake lines can cause the brake pedal to be soft and spongy.

Brake Fluid Flush 

If you have a soft brake pedal, this could be a good time to change or flush the brake fluid and maintain its integrity and health. Flushing the brake fluid, also known as bleeding the brakes, could eliminate the cair in the braking system. This process involves using fluid to push out the excess air out of the brake system. 


Over time and after prolonged use, the brake fluid absorbs the moisture and pushes out the air. Flushing the brake fluid prevents the old fluid from boiling, which can cause the soft brake pedal. If you keep the integrity and the health of the oil, make sure you keep clean and fresh fluid. A brake flush can protect and preserve the other brake components and prevents further and more expensive replacements. 


Keeping your brake fluid and the oil in good condition can save components like the master cylinder and the anti-lock brake system from further issues. The master cylinder is the control device that converts force into hydraulic pressure, controlling cylinders at the opposite ends of the hydraulic system. It is the first component of the braking system and is activated by depressing the brake pedal, and can prevent the soft brake pedal. 

Brake Fluid Flush Cost

The cheapest place to go for the lowest brake fluid flush cost is Pep Boys, Firestone, Jiffy Lube, and Big O Tires, costing around $69 for the brake fluid flush cost. The next cheapest option is around $80 for the replacement, while Midas comes in at $85. The most expensive place to bring your vehicle for the brake fluid flush is Brake Masters, costing you around $130 for the service. 

  • Damaged or Leaking Brake Line

Since the brake lines are made of steel in the tubing over time, the crust can build up on the lines and cause corrosion. Over time, the rust can cause small holes and damage in the steel tubing to develop, causing the brake fluid to leak out of the system. If you lose brake fluid in your engine, this can lead to a loss of hydraulic pressure, so the brake pedal will end up spongy and cause the soft brake pedal.

Brake Fluid Leak Symptoms

Brake Light On – This is usually the first sign and the most noticeable that you might be having a brake fluid leak. The brake light can alert the driver to the problem with the brakes since the warning light illuminated on your dashboard is easily noticeable by the driver. It might not necessarily mean that you have a brake fluid leak, but it can be a sign of a soft brake pedal.


Puddle of Brake Fluid –  If you notice a small puddle of brake fluid near the wheels or on the wheels under the car, then the brake fluid leak is usually occurring in your vehicle. If the brake master cylinder leaking or the brake lines are leaking, then there is a brake fluid leak that will make it difficult to determine whether it is leaking brake fluid, transmission fluid, or motor oil. 


To determine what kind of oil is leaking from your car, brake fluid is light yellow or clear and has an oily feel and a rancid smell of fish oil. The fluid’s color makes it easy to confirm that the brake fluid leak occurs and on the ground and causes the soft brake pedal. 

  • Leaking Disc Brake Calipers

Similar to brake lines in your car, the disc brake calipers can also become corroded with rust due to the buildup of damage over time. The brake disc calipers are the component that clamps the brake pad down against the brake rotors to slow down the vehicle by pressing on the wheels. If the brake disc calipers become corroded, the internal piston seal can leak the brake fluid from the fuel system.


If the disc caliper is leaking, it can cause the soft brake pedal and cause the pedal to go very low to the floor. A brake pull can also be experienced at the same time if there is not enough fluid within the brake caliper. 

  • Damaged Master Cylinder

The master cylinder is the control device that converts mechanical force, like you pressing your foot on the bare pedal, into hydraulic pressure. As pistons move along the master cylinder, this movement is transferred through hydraulic fluid, converting to the cylinders’ movement. 


The master cylinder is the center of the brake system and performed a number of very important functions, like holding the brake fluid, generating the hydraulic pressure for baking powder, and feeding the pressure to the front and rear brakes to stop your car. Unfortunately, the master cylinder can wear out over time and become damaged over time, developing leaks and causing a soft brake pedal. 


There are two main types of cylinder leaks – either an external brake fluid leak or an internal leak from the damaged piston seal. Either of these leaks can cause a soft brake pedal since both failures can cause a loss in hydraulic pressure on the brakes, causing the brake pedal to fail and go to the floor.

Master Cylinder Cost

If your brake master cylinder ends up going bad, the average cost to replace the cylinder will usually be between $320 and $500. The most significant expense when replacing the brake master cylinder in your car is the labor costs, which will come in between an average of $230-$300 for the total brake master cylinder cost. 


Figuring out the total master cylinder cost for a replacement can depend on what service you use and the type of car you have (i.e., the make, model, and year). You can use a website to determine your car’s total price since the range can go from around $240 to a whopping $2433 for a replacement. 

  • Leaking Wheel Cylinders

Some cars contain disc brakes on the front wheels and drum brakes on the rear wheels. Disc brakes are kinds of brakes that use calipers to squeeze pairs of pads against the disc or rotor to create friction. This action is in charge of slowing the shaft’s rotation to reduce the rotational speed and hold it stationary. 


The disc brakes can be either hydraulic disc brakes or mechanical disc brakes, depending on how the brake pads are controlled. Mechanical disc brakes use cables to move the pads, while hydraulic systems have fluid-filled brake lines. Hydraulic brakes offer a smoother performance than other brake systems, while the disc brake’s performance is more consistent. 


Drum brake systems feature a drum that rotates along with the wheel, while inside of the drum is a set of brakes that are forced against the drum by the pistons in the wheel cylinder. The three-wheel cylinder piston moves against the brakes due to the brake pedal’s hydraulic pressure being depressed. If there is a soft brake pedal, this will not happen.

  • Rear Brake Shoe Adjustment

If your car or vehicle has a rear brake drum and pumping the brake pedal improves the pedal, then the braking drum might be damaged or out of adjustment from common use, resulting in a soft brake pedal. This issue could be that the rear brake drum is not being adjusted over prolonged periods of time and use. 


Make sure you or your mechanic checks your rear brake drum for wear and tear and is adjusted as needed. Be sure that the parking brake is occasionally checked and occasionally used an ABS measure to ensure it is working correctly and preventing a soft brake pedal. Using the parking brake causes an automatic adjustment of the brake shoes and the brake drum, resulting in a soft brake pedal. 

  • ABS Assembly Malfunction

Vehicles that have the ABS system also have a hydraulic assembly called the ABS modulator. This assembly contains multiple internal solenoids and valves, meaning that if you have an internal failure, corrosion, or debris in the brake fluid, this can result in the soft brake pedal and the valve not operating correctly. 

Diagnosing a Soft Brake Pedal

  • Booster Pin Gap

You can diagnose the soft brake pedal by the booster pin gap. The booster pin gap between the brake booster goes into the back of the master cylinder and gives the feeling of a spongy or soft brake pedal. In this scenario, it usually will feel like nothing is happening, and then all of a sudden, the soft brake pedal occurs. 

  • Determine the Master Cylinder Bore Size

Furthermore, you can also diagnose the soft brake pedal by figuring out the incorrect master cylinder bore size. A major contributor to a soft brake pedal can be the master cylinder bore size is incorrect for the entire system. 


Calipers with multiple small pistons usually use a smaller bore size. Still, if the bore size is too small in the master cylinder, it can take more travel to generate the proper volume and line pressure to get the right piston travel in the caliper. Getting the right master cylinder bore size is key to getting the right amount of line pressure and preventing a soft brake pedal. 

  • Recognize Any Component Failure 

Component failure is another way to diagnose a soft brake pedal, like problems with the wheel cylinders or calipers. The master cylinder usually dictates that the internal seals have failed, and can be dangerous when a sot pedal gets worse. 


Pump the pedal gently and then hold the brake pedal, and if you see it creep downward, you are more than likely to have a master cylinder that is leaking internally and not able to keep the right amount of pressure, causing a soft brake pedal. 

  • Inspect the Brake Hose

You can also diagnose a soft brake pedal to determine if the brake hose is leaking. If the brake hoses are old, they can be leaking air through the outside of the house, meaning that air can enter and exit the hose and be the same as a fluid leak. Unfortunately, there isn’t a way to diagnose this problem without fixing and changing the hoses by solving the soft brake pedal. 

  • Check for Mechanical Interference

There are instances where everything works fine, but suddenly the pedal will become soft and spongy. In this situation, the caliper could contact the frame or suspension and push against the caliper and flex the caliper too much or cause it to slide on the pins. If this happens, the fluid is pushed out of the caliper and pressed on the brake pedal, causing a soft brake pedal. 


Now that you know the main causes of why a soft brake pedal occurs in your vehicle, you can take the steps necessary to prevent this issue from happening and getting any worse in your car! 


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