6 Causes of Spongy Brakes (or Soft Brake Pedal)

Last Updated on June 13, 2022

Every driver knows how it’s supposed to feel when they hit the brakes. So, when something doesn’t feel right, it’s essential to track down the problem’s cause and fix it right away.

The good news is that while spongy brakes are a common concern, it’s usually a pretty straightforward fix, and if you know what you’re doing, it typically doesn’t have to cost you a ton of money.

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Below we’ll break down the most common causes for spongy brakes, then walk you through everything you need to know to help diagnose it if you have a problem in the first place!

Top 6 Reasons for Spongy Brakes

Spongy brakes aren’t just annoying – they’re dangerous. If you’re feeling anything weird going on when you step on the brakes, check out the following five reasons that it might be happening.

#1 – Air In the Brake System

brake fluid leak symptoms

Having air in the brakes is by far the most common reason for spongy brakes. But just as crucial as getting the air out is determining how it got there in the first place. If you recently had work done to the brake system, that’s a likely culprit.

Otherwise, you probably have a leak somewhere that you need to look into. Start by bleeding the brakes and see if the problem continues. If the problem persists after bleeding the brakes, keep reading.

#2 – Damaged Brake Lines

damaged brake line

While there are plenty of components that can get damaged, the brake lines are the most common. This is more common in coastal towns and states with lots of rock salt on the road. Both of these things cause corrosion, and the brake lines have no protection from any of it.

The longer it goes on, the more likely they are to rust, leading to leaks that allow brake fluid to escape and air to enter the system.

#3 – Old Brake Fluid

brake fluid change

While brake fluid can last a while, it’s not something that can last forever. While some manufacturers have set service intervals ranging from 20,000 to 30,000 miles, the truth is a little more complicated.

That’s because as long as the brake system doesn’t have any leaks, the fluid itself can last over 100,000 miles. But as soon as air gets introduced to the system, it starts to oxidize and add moisture to the fluid.

This is detrimental to your brake system. The more moisture that gets added, the spongier your brakes will feel, which is a telltale sign that you need to flush the system and change your fluid.

Related: DOT 3 vs DOT 4 Brake Fluid

#4 – Leaking Brake Booster

bad brake booster symptoms

Another critical component in your vehicle’s braking system is the brake booster. The brake booster amplifies the amount of force you generate by pressing on the brake pedal.

While this is a helpful feature, if any of the seals start to fail in the booster, you’ll end up with spongy brakes. If you suspect a faulty brake booster check out this helpful guide on how to diagnose it!

#5 – Damaged Master Cylinder

bad brake master cylinder symptoms

While your brake lines can rust and leak, there are seals throughout your master cylinder that keeps everything working the way it should. If you have a broken seal in the master cylinder, one of two things can happen depending on the leak’s location.

First, brake fluid can leak out of the cylinder, which can lead to spongy brakes. Second, if the leak is above where the brake fluid sits – like at the cap – air will get into the system.

Not only can this air cause problems, but the moisture that it attracts will deteriorate the brake fluid—both result in spongy brakes. You’ll have to fix the leak and flush the brake fluid to keep the problem from coming right back.

#6 – Damaged Brake Calipers

remove brake caliper

Another common area to have a leak is around the brake calipers. The brake pistons have seals that keep the fluid where it’s supposed to be, but a leak can result if those seals start to break down.

While this isn’t super common, it’s a big problem if it does. Not only will you have spongy brakes, but you’ll also have low brake fluid and brake fluid around the rotors and brake pads.

If you have a leaking brake caliper, you need to get it fixed immediately.

See Also: Sticking Brake Caliper (Symptoms/Causes)

Is It Safe to Drive With a Spongy Brake Pedal?

If you have spongy brakes, it is NOT safe to drive, and you need to repair the underlying fault as soon as possible.

Spongy brakes are one of the most dangerous problems your vehicle can have. It’s indictive a deeper problem, and more importantly, it prevents you from stopping as quickly as you should.

Spongy brakes could mean that you have a leak, and small leaks can turn into a big one with just one push of the brakes.

If your leak turns into a blowout, you’ll have a complete loss of brake pressure. It won’t just take you longer to stop – you won’t be able to stop at all!

Even if your brakes aren’t leaking, spongy brakes mean that there is air in the system. The softness you feel while pressing the pedal is air hitting the caliper – when this happens, your brakes aren’t working.

It’s going to take you longer to stop, and it’s just going to get worse until you fix it.

Related: 5 Reasons Brakes Can Lock Up

Diagnosing a Soft Brake Pedal

soft brake pedal

When pushing on the brakes, you should feel solid pressure from start to finish. If it feels as though the brake pedal’s pressure is changing when you press the brakes or if the brakes feel mushy, you have a spongy brake pedal.

Spongy brakes feel like squishy brakes, and it means the same thing.

There is an additional test you can conduct to try and locate the source of the problem. One of the best tests you can perform is to turn the key off and pump the brakes a few times. Once the pedal gets hard, push down on the brakes.

If the pedal starts to sag to the floor after this, you have a leak somewhere in the system, and you know the problem is deeper than just a little air you need to bleed out of the system.


8 thoughts on “6 Causes of Spongy Brakes (or Soft Brake Pedal)”

  1. i have disc in the front new pad, new hose new calipber both side
    new proportion valve with centered and locked shuttle valvle
    new shoes and wheel cylinders in the back
    all new fluid

    spongy pedal bleed all ways still very spongy and low pedal at a loss help, brian doyle

  2. My 2009 Honda AWD CR-V brake pedal started getting soft and traveling closer to the floor. If I pump the brakes the pedal gets firm until braking again. I bled the brakes and noticed some air bubbles, flushed and replaced fluid with Prestone DOT3. About 2-3 weeks later the problem returned. A shop mechanic checked, found air bubbles in the front, replaced the front calipers, the problem returned again in about 2-3 weeks. I see no leaks at the master cylinder, booster, calipers or lines (as much as I can see of them). I’ve done your recommended booster tests, checks OK. Any further ideas would be appreciated.

  3. 2010 mercury milan. has new brake pads, brakes were bled, no visible leaks.
    what could be the problem? brake pedal goes nearly to floor, little braking action

    • I guess the next thing I would check would be the rubber brake hoses. Make sure none of them are swelling or doing anything strange when you press on the brakes.

      I would also double check that the brakes were bled properly and that there is no air in the lines, especially if you have ABS. Air can get trapped inside the ABS module and often requires a professional to properly bleed.


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