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Soft Brake Pedal – What Are The Causes?

Brake Pedal Goes To The Floor

A brake pedal that is functioning correctly 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 a situation when the brake pedal does not have firmness, and can cause an unsafe situation for you and your passengers. 

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Causes of a Soft brake pedal


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 usual when you are trying to stop your car, then 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 main causes of a soft brake pedal is that there is air in the brake lines. 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. This can cause the brake pedal to be soft and spongy.


If you have a soft brake pedal, then this could be a good time to change or flush the brake fluid and maintain the integrity and health of the brake fluid. Flushing the brake fluid, also known as bleeding the brakes, could get rid of 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, then make sure you keep clean and fresh fluid. This 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. 

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, which can cause 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.

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 in order to slow down the vehicle by pressing on the wheels. If the brake disc calipers become corroded, this can cause the internal piston seal to 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. 

Worn 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 a result in a movement of the cylinders. 


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, over time, the master cylinder can wear out and become damaged over time, develi9png 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.

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 rotation of the shaft 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 brakes performance is more consistent. 


Drum brake systems feature a drum that rotates along 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. Three wheel cylinder piston moves against the brakes due to the hydraulic pressure generated from the brake pedal being depressed. If there is a soft brake pedal, this will not happen.


Corrosion inside of the wheel cylinder can cause the brake fluid to leak, resulting in a loss of hydraulic pressure and resulting in the soft brake pedal. 

Rear brake shoe adjustment 


If your car and 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 form 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 occasionally is checked and use it occasionally as a preventative measure to make sure 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 hydraulic 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 to not operate at the correct level. 

How to diagnose a soft brake pedal


Many people ask why they have a soft brake pedal in their car – and this is a problem that needs to be resolved so that you can drive safely and confidently. There are some very common reasons as to why you might have a soft brake pedal, but there are ways to diagnose a soft brake pedal in your car. 


First, the most common reasons could be air in the system. The easiest way to diagnose if this is the issue behind a soft brake pedal is to pump the brake pedal a few times. In doing so, the pedal should become firmer – if it does, then the approach of bleeding the brakes can be a quick diagnostic. 


However, the hardest part about getting the extra air out of the system is that you can’t visibly see the air that is leaving and how much air needs to leave. You can find the extra air by finding a kink in the brake line, a bend in the brake line, or a high point in the brake caliper. To remove the air in a caliper, you might have to remove the caliper and move it around to get out the air to solve the soft brake pedal. 


The second way you can diagnose the soft brake pedal is by determining if there are any fluid leaks in the system. The first part of this is any visible brake fluid that is leaking from a fitting. If the fluid is leaking, then the system will never be able to reach a point where it can move within the calipers, causing a soft brake pedal.  


The other part of this is when there is a brake fluid leak but there is no fluid coming out. If this happens, it is possible for the fitting to up air when the pedal is going back to its original position. The air entering the system causes a situation where the brakes need to be bled again, but you need to fix the cause of the soft pedal.


Another way to diagnose the soft brake pedal is by contaminated brake fluid. Brake fluid is like the oil in your engine and is recommended to change your brake fluid once every two years. If the fluid goes too long without being changed with routine maintenance, the fluid can absorb moisture, and then cause the soft brake pedal.


In addition, 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. 


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, but if the bore size is too small in the master cylinder, then it can take more travel to generate the proper amount of 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. 


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 having a master cylinder that is leaking internally and not able to keep the right amount of pressure, causing a soft brake pedal. 


Another way that you can diagnose a soft brake pedal is to determine if the brake hose is leaking. If the brake hoses are old, then they can actually 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. 


Lastly, the final way to diagnose the soft brake pedal is by checking out any mechanical interference. There are instances where everything works fine, but all of a sudden the pedal will become soft and spongy. In this situation, the caliper could come in contact with 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. 

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