Why Do My Brakes Feel Spongy?
Ellie Dyer-Brown, 10 days ago
5 min read
- Brakes
- Diagnostic
FixMyCar explains why your car's brakes might feel spongy.
Problems with the brake lines, callipers, master cylinder, wheel cylinders, brake fluid or anti-lock braking system could cause spongy brakes or a brake pedal that sits close to the floor. This guide explains each possible cause with repair advice and average costs, helping you feel more confident about understanding the problem and booking a repair.
Contents
In a nutshell: Spongy brakes are usually caused by faults in the braking system, such as low brake fluid or a faulty master cylinder. Continuing to drive a car with spongy brakes is dangerous and not recommended. Instead, you should book a repair as soon as possible.
Read this guide for a detailed explanation of how car brakes work.
Symptoms of spongy brakes
We all know what sponges feel like, but understanding how this sensation applies to your brakes isn’t necessarily straightforward. Here’s are some other symptoms to look out for.
Your car’s brake warning lights stay on
If one or all of your brake warning lights are on, it could be due to worn brake pads, hydraulic issues or a range of other things. You should never ignore your car’s warning lights.
The brake pedal continues sinking
If you notice your brake pedal goes down with little to no resistance and keeps sinking even after you’ve stopped applying pressure, you should contact a garage or mobile mechanic as soon as possible to arrange a repair.
Your master cylinder may need replacing, there might be a problem with the ABS, or there could be a fluid leak in the braking system.
You have to pump the brake pedal to slow down
When you have to pump the brake pedal to get it to work, this often indicates a fluid leak or your master cylinder is faulty.
Why are my brakes spongy?
Spongy brakes can be caused by various problems with the braking system. Here are the most common causes.
1. Low brake fluid
Brake fluid converts the pressure from you pushing the brake pedal into braking force, making the vehicle slow down and stop.
While spongy brakes can be alarming, they don’t always signal a serious (and expensive) problem. The cause could be something simple and cheap to fix, such as low brake fluid, in which case all you have to do is top it up.
This guide explains how to check and change brake fluid.
If your brake fluid level is frequently low, even after you’ve topped it up, there could be a leak that needs repairing due to corrosion from moisture, salt or general wear and tear.
2. Old or contaminated brake fluid
Just like engine oil, your brake fluid needs checking and replacing every so often to ensure it is clean and able to perform as expected. You should aim to change your brake fluid and flush the system once every two years.
While brake fluid is checked during a full service, it isn’t usually replaced - this is something you may have to pay extra for or book separately. If you leave your brake fluid too long, it can absorb moisture, changing the compression characteristics, which may impact how your brakes feel and their overall effectiveness.
Likewise, some types of brake fluid can’t be mixed as they will gum up the system. A complete flush of the brake system is needed to fix this problem.
A brake fluid change costs £58.31 on average, according to our data.
3. Faulty master cylinder
The master cylinder uses brake fluid to convert the pressure on the brake pedal into hydraulic pressure by feeding it into the brake circuit, controlled by mechanical force. When it is faulty or broken, even if you have sufficient fluid, the system won’t be able to operate, causing your pedal to feel spongy or sink entirely to the floor.
You can expect to pay around £200-300 to have a new master cylinder fitted.
4. Air in the brake lines
Air usually enters your brake lines when there isn’t enough brake fluid, and since it is less dense, it compresses too easily, making your brakes feel spongy. Driving with compromised hydraulic pressure is dangerous, so you should have your brakes checked by a mechanic as soon as possible.
5. Misaligned rear brake shoes
When a vehicle’s rear brake shoes are out of adjustment, you may have to pump your pedal to get it to work, eventually leading to faded or spongy brakes.
6. ABS modulator issues
The anti-lock braking system modulator is a hydraulic assembly that optimises brake pressure. When the modulator is damaged, it may cause the brake valve to malfunction, resulting in a spongy feeling when you press the brake pedal.
Learn more about why your ABS warning light might come on here.
7. Wheel cylinder leak
Wheel cylinders are found in hydraulic drum brakes. They force apart the brake shoes, pressing them against the drum. When you press the brake pedal, it generates hydraulic pressure in the master cylinder, which is transmitted via brake fluid to the wheel cylinder, where it acts on the pistons.
Corrosion can cause small holes in the wheel cylinder where fluid leaks out. When the brake fluid level is too low, you’ll notice your brake pedal feeling spongy or sinking independently.
On average, car leak repairs cost £81.98 when booked through FixMyCar, though the price varies significantly depending on the type and location of the leak.
8. Damaged brake calliper
Brake callipers push the brake pads against the rotors, which generates a lot of heat from friction. Over time, the combination of heat and general wear can corrode or damage the callipers, affecting the fluid pressure and, in turn, how your brake pedal feels.
How to fix spongy brakes
Until you know the exact cause of your car’s spongy brakes, it’s impossible to say for sure what the best fix is. That’s why you should seek advice from a mechanic.
Temporary fix: pump the brake pedal
It’s best to arrange a brake repair as soon as possible. However, it’s essential to know what to do if your brakes start feeling spongy while you’re driving. In this situation, repeatedly pumping the brake pedal should generate enough pressure to stop the car safely.
You can also do this to test for a loss of pressure, which may indicate the cause of the sponginess.
Check for any obvious leaks
Looking for leaks is one of the first things a mechanic will do to find the cause of spongy brakes. They will usually inspect the fluid level of the master cylinder and check for any pools of brake fluid behind the wheels and under the bonnet.
Flush or bleed the brakes
When air is in the brake lines, a mechanic will usually flush the system to get rid of it before adding new fluid.
If you need help fixing spongy brakes, FixMyCar can help you find the right garage at the right price. Access the UK’s biggest network of independent garages and mobile mechanics in just a few clicks.
Frequently asked questions
How do you get air out of brake lines?
The only way to remove air from your car’s brake lines is to “bleed” the brakes. This term refers to draining the brake system to remove air bubbles before topping it up to the correct level. Learn how to check and change brake fluid in this guide.
It usually costs between £40-50 for a brake fluid change.
Why are my brakes still spongy after I bleed them?
After you have bled your brakes correctly, there should be no air in the system, which indicates something else is causing the spongy feeling, such as contaminated brake fluid or a leak in the system. At this point, it’s best to consult a mechanic, as the repair will be more complicated than simply changing your brake fluid.
Why does my brake pedal go to the floor when the fluid is full?
The most likely culprit is a faulty master cylinder, which must be replaced. Typically, replacing a master cylinder costs around £200-300.
Is it safe to drive with spongy brakes?
It is not safe to drive with spongy brakes. Any unusual behaviour from your car’s brake system signals a problem, so you should stop driving and seek professional advice.
Are brakes supposed to feel soft?
Your brake pedal isn’t supposed to feel soft - it should be firm but not hard when you push it down, and your brakes should be reactive. If they feel too soft, too hard or different in any way than usual, it indicates a problem.
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