Why is My Brake Pedal Sinking?

If you’re noticing that your brake pedal feels unresponsive, spongy, or even sinking to the floor of your footwell, it likely means there’s an issue within your braking system causing a loss of hydraulic pressure.

Your brakes operate using hydraulic fluid to transfer and amplify forces from the pedal to the caliper of the brakes, which pushes the pads into the rotors creating friction to stop the vehicle. When any part of this system responsible for creating hydraulic pressure fails, it will cause issues within the entire system.

In this article, we’ll go over the common causes of a sinking brake pedal, why it occurs, and how you can prevent this issue from happening in the future. 

Common Cause of Sinking Brake Pedal

Faulty Master Cylinder

The master cylinder is the component responsible for taking the force applied to the brake pedal and converting it into hydraulic pressure. Within the master cylinder, multiple cup seals ensure that hydraulic pressure can be built up and contained behind the cylinders and within the compartment. 

Over time, these seals and gaskets will begin to break down and potentially allow fluid to bypass. As the seal is no longer able to prevent internal leakage, the hydraulic pressure within the system will be lost. 

When attempting to brake with decreased hydraulic pressure, you’ll notice a spongy feeling as the lack of pressure prevents the proper amount of resistance in the pedal. In some cases, this could lead to the pedal sinking to the floor on its own due to this lack of resistance.

Leaking Brake Fluid

As your brake system relies on hydraulic pressure, ensuring it’s running with an adequate amount of brake fluid is crucial. Without the proper volume, it will be impossible to produce sufficient hydraulic pressure as there won’t be enough fluid in the system to transfer the force through. 

This issue is likely due to an external fluid leak somewhere within the lines or components of your brake system. If you notice a puddle of oil-like fluid beneath your vehicle, it could potentially be brake fluid that has leaked. Oftentimes when fluid is leaking, it also means that air is entering the system, causing the remaining fluid to become aerated (or full of bubbles and air pockets).

Contaminated/Aerated Brake Fluid

A similar effect can occur when your fluid becomes aerated from the inside. Due to brake fluid being hygroscopic, or able to take on moisture from the surrounding atmosphere, the system may become contaminated with water. Not only will this cause increased corrosion of sensitive brake components, but it also allows for this moisture to boil off within the system due to the vehicle’s heat. As the moisture boils away into gas, your fluid may become aerated with bubbles and air pockets that disrupt hydraulic pressure. 

How Can I Prevent Low Brake Pressure

Now that you know the common issues that lead to a spongy or sinking brake pedal, it’s important to understand how to prevent these symptoms from occurring in the future. 

The best way to prevent problems with your brake fluid is to change it at the recommended interval. Though your brakes might not have an issue at the moment, allowing your system to continue running contaminated or low fluid will cause increased wear and the potential for further leaks. 

We recommend that you have your brake fluid replaced every few years, or around every 30,000 miles. This will give you the longest healthy life from your current fluid while preventing it from reaching a contaminated and harmful condition. 

Brake Services at Lake City Auto Care

If you’re experiencing a sinking or spongy brake pedal, trust the experienced technicians at Lake City Auto Care to return yours to feeling like new. Don’t let a brake issue linger, as it will likely only worsen and lead to a more costly repair. 

Give us a call or schedule online at one of our three Northern Idaho locations today! We’re located in Coeur d’Alene, Hayden, and Rathdrum. Our team is excited to take care of you and your vehicle.