Spongy or Soft Brake Pedal?

If your brake pedal feels spongy or soft when you press it and it takes more effort and force to brake, you’re experiencing brake fade. Brake fade is a loss in braking power, and it’s usually because there’s an issue with the brake fluid. Find out how to fix this problem with tips and advice from our experts in this article and video.

What Causes a Spongy, Soft Brake Pedal?

A spongy or soft brake pedal can be caused by brake fade, which is a loss in stopping power from the brakes due to the heat generated by them. It can be caused by frequently braking and stepping on the brake pedal too much, or another failure in the brake system like a stuck brake caliper or contaminated brake fluid.

What Is Brake Fade?

Spongy Brake

Brake fade happens when a hydraulic braking system has temporary or complete loss of braking power from hot brake fluid that vaporizes, caused by excessive friction from the brakes. The brakes will be less effective at stopping and the brake pedal will feel spongy or soft.

What Causes Brake Fade?

Excessive Heat

Most passenger vehicles will have a hydraulic braking system. This means the brake system uses fluid pressure to stop the vehicle. When you press the brake pedal, parts in the brake system work together to create pressure and send brake fluid to the brakes. This pressure pushes the caliper piston into the brake pads, which then press into the spinning brake rotor. When the pads press into the rotor, friction is created, and this friction slows the wheel to a stop.

Heat is a result of this friction, and the brakes get hotter the more you press the brake pedal when the car is moving. If the temperature exceeds the brake fluid’s boiling point, the fluid will boil and vaporize. Vaporized brake fluid has a lower compression rating and provides less braking power, and this brake fade can be felt when the brake pedal is depressed and feels soft or spongy, making the vehicle less safe and effective at stopping.

Contaminated brake fluid is a common cause of a spongy or soft brake pedal because its boiling point will be lower than newer, fresh fluid, making it more susceptible to vaporizing and working less effectively.

Frequent Braking

Repeated braking to the point where the brakes can’t cool before reaching the brake fluid boiling point will cause the brake fluid to vaporize. This can happen, for example, when driving in stop and go traffic.

Different types of brake fluids will have different boiling points, and they will be labeled on the bottle. Old and contaminated brake fluid will have a different boiling point from newer fluid—especially if the old fluid has been contaminated with moisture.

Is Brake Fade Dangerous?

Brake fade is a major safety issue. If you feel like you’ve lost the ability to stop quickly, get it diagnosed and fixed as soon as possible and don’t attempt to drive the vehicle.

How Can I Prevent a Soft Brake Pedal Due to Brake Fade?

Don’t Brake Excessively

To prevent brake fade, don’t ride the brake and brake when necessary not excessively.

Buy Drilled and Slotted Rotors

One way to prevent brake fade is to buy drilled and slotted rotors to help with heat dissipation.

How to Diagnose and Fix a Soft Brake Pedal and Brake Fade

Steps to Diagnose and Fix a Soft, Spongy Brake Pedal

  1. Check the Master Cylinder and the Condition of the Brake Fluid

    The cover on the master cylinder will show what type of brake fluid to use, which could be DOT 3, DOT 4, or in a specialty car DOT 5.
    Remove the cap and look inside the master cylinder to check the condition of the brake fluid. The brake fluid should look clear. If it looks dirty or has debris, or it looks like it has a film or cream on top, it is contaminated and the fluid needs to be replaced. Old, contaminated, and moisture-filled brake fluid will probably have a lower boiling point than new brake fluid.

    It can be difficult to inspect the brake fluid inside the master cylinder. It might be easier to see the fluid level marked on the side of the reservoir, but sometimes it can be hard to see the brake fluid. Testers can help you analyze the brake fluid by testing for acidity and moisture.

    One way to guess if your brake fluid needs changing or flushing is to check the odometer. If your vehicle has been driven for over 200,000 miles and you’re unsure of the last time the brake fluid was replaced, it might be overdue.


  2. Replace Contaminated Brake Fluid

    If you found the brake system was contaminated, the best you can do is flush the brake system. Use the proper fluid when doing this. DOT 3 and DOT 4 fluid are interchangeable and you can add one to the other, but this isn’t best practice because DOT 4 is more expensive and has a higher temp rating, and it won’t change the fluid much if it’s added to DOT 3 fluid.

    If you find you need to put a lot of pressure on the braking system, take out all the DOT 3 fluid in the braking system and replace it with DOT 4. DOT 4 has a higher temperature rating, especially in extreme conditions like towing something or going down a hill where you need to frequently or aggressively brake.

    If replacing or flushing the fluid out, keep the master cylinder full with fresh fluid. Letting the fluid level fall down too far and letting it suck air into the system could cause issues, especially with an ABS unit in the car.

    Tip: Don’t add DOT 5 to systems with DOT 3 or DOT 4 brake fluid. While DOT 3 and DOT 4 are interchangeable, but DOT 5 is a different fluid. DOT 3 and DOT 4 are hydroscopic, meaning they can absorb moisture. DOT 5 is hydrophobic, meaning it will repel moisture. If you mix them, it can cause a major issue with the braking system.

  3. Check If the Brake Caliper Is Stuck

    Don’t just focus on the fluid. Maybe you haven’t driven the car too long, like only 20,000 miles, but find you have an issue. There could be an issue with the brake caliper or the braking material.

    If the brake caliper is stuck in the position with the pads against the rotor, the rotor won’t spin easily since the pads are grabbing it tightly. Friction causes heat, and this can cause other symptoms like smoking brakes.

    Make sure the brake caliper piston is functioning. If it is in good condition, it will press in easily. Make sure the caliper slide pins are greased and sliding without getting stuck. If they are stuck, grease them.

  4. Inspect the Condition of the Brake Line Hose

    Inspect the brake flex hoses. Wiggle and make sure they’re not dry rotted and cracked. If a bubble forms on them, it can expand when there is more brake pressure from the brake pedal.

  5. Check the Cooling Fins on the Rotor

    Inspect the cooling fins on the rotor. Rotted and flaking cooling fins won’t help with heat dissipation and can cause the brakes to overheat.

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Spongy or Soft Brake Pedal? Diagnose Brake Fade - 1A Auto
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Spongy or Soft Brake Pedal? Diagnose Brake Fade - 1A Auto
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If you have a soft or spongy brake pedal and you've noticed a decreased in stopping performance, your brakes need to be inspected. Learn how to diagnose them with these expert tips in this article and video
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1A Auto
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