This page is dedicated to helping you figure out why your brakes feel spongy. On this page, you’ll find a short video outlining the one-person brake bleed procedure. I’ll also share some mechanics top tips for brake repair together with links to tools you’ll need.
Mechanics Spongy Brake Repair Tips
While a spongy pedal doesn’t prevent your brakes from functioning, it does compromise safety and your confidence in the vehicle. Spongy brakes are serious and obviously need investigation immediately. The most common reason a brake pedal feels soft or spongy is – air in the brake lines.
As you apply the brakes and pressure the fluid, the air in the lines compresses and allows the pedal to sink to the floor creating that spongy feeling. The fix here is to bleed the brakes and that’s covered in the video above.
However, air in the system isn’t the only cause of a spongy brake pedal feel. Here are a few of the more common ones together with some repair tips.
New Brake Pads Fitted
It’s common for brakes to feel spongy after fitting new brake pads. The pads must bed in and until they do (usually 8-10 brake applications) the pedal won’t inspire confidence. This assumes of course that the brake caliper bleed screw wasn’t opened during the pad fitting process.
Contaminated Brake Fluid
Brake fluid should be changed every four years at least. Brake fluid attracts moisture and that promotes corrosion but also causes the water in the fluid to boil as the brake system heats up. When the water boils it turns to steam and that causes a spongy brake pedal feel.
If your vehicle suffers from this condition, a fluid flush will fix it.
Brake System Leak
Brake fluid is crucial to brake application, the pressure you apply to the brake pedal is immediately transmitted through the fluid and the force is applied to all four wheels brake calipers/cylinders. If system fluid is low it extends the time to activate the brakes and that can make the difference in an emergency situation.
A brake system employs a master cylinder, metal and rubber hoses, an ABS modulator, and calipers or wheel cylinders.
The master cylinder, caliper, ABS modulator, and wheel cylinders all incorporate seals to keep fluid and pressure in and grit and dirt out. A perished or damaged seal will cause a fluid leak.
Metal pipes run from the front of the vehicle to the rear carrying the fluid, they tend to corrode with age and increasingly so in salt states. The corrosion promotes pinholes which cause leaks.
A leak in any of these components will cause a soft pedal. And obviously, a leak is very dangerous, luckily it is usually easy to spot. Check the fluid reservoir under the hood and also check under the vehicle and pay particular attention to damp or wet patches.
Brake Rotors Warped
A warped or wabble if you like in the brake rotor serves to push the pads away from the rotor and back into the brake caliper. Each brake application, therefore, requires more brake pedal travel to push the pads back out.
Warped rotors are a common complaint and mean your rotors and pads need to be replaced. A single warped rotor may mean you have an underlying issue with the brake on that wheel, typically a dragging caliper.
Rear Shoe Adjustment
Many trucks and older cars employ brake drums at the rear instead of rotors and calipers. Drum brakes require adjustment, most are self-adjusting but they don’t always work as they should.
When the shoes wear down and they don’t self-adjust they move further away from the drum resulting in increased brake pedal travel. Adjusting or replacing the shoes will solve this issue.
Flexible rubber hoses are employed to carry fluid from the chassis out to the wheel. As the wheel is dynamic, metal hoses would simply break.
The rubber hoses then flex as the suspended wheel moves up and down. The constant movement does cause the rubber hoses to fatigue as does the internal brake fluid pressure.
Brake hoses are twin-lined for safety. If the inner layer breaks, the outer will contain fluid pressure. However, a single outer layer of rubber isn’t sufficient to contain the fluid pressure and the rubber hoses expand which results in a spongy brake pedal feel.
Replacing all flexible rubber hoses will help fix this issue.
Spongy Brake Diagnosis Tip
There are a ton of components in a brake system. And after making the usual inspections, fluid level, leaks, etc. you can try this tip to help diagnose a system-wide or localized fault.
Clamp off each wheel’s flexible hoses in turn and check brake pedal feel (not on the road). Finding or not finding a difference helps you figure out what’s going on.
Brake Repair Tools
Here are a few tools to help you nail the spongy brake repair like a pro!
Brake fluid moisture tester, this simple tester is a really fast way to check the moisture content of your fluid. Brake fluid should be changed every three years. Moisture inside the hydraulic system is as you know bad for a couple of reasons.
First, it reduces brake performance when the fluid gets hot and second moisture inside the system attacks metal components causing corrosion. This will lead to caliper, brake line, master cylinder, and possible brake controller damage. Picture links to Amazon.com.
Useful one-man vacuum brake and clutch bleeding kit that won’t hurt the pocket. It’s perfect for occasional brake maintenance chores, easy to use, and gets the job done. Picture links to Amazon.com.
Compact brake line flaring tool, the best thing about this tool is its size. This little guy is ideal for flaring brake lines while on the vehicle, but the handle is detachable for bench work too. Flares 3/16 SAE double flare steel and copper. Picture links to Amazon.com.
The Autel MaxiCOM is a shop-level tool. It is capable of reading, clearing fault codes, coding a new battery, placing EPB module in service mode, and calibration after the repair. It is also capable of activating ABS modulator solenoids when performing a full brake bleed procedure. Picture links to Amazon.com.
Preston is a leading supplier of quality automotive fluids. This is DOT 3 so remember to check your reservoir cap before ordering. This product is sold by Amazon and is conveniently delivered to your door. Picture links out to Amazon.
3M make top-quality products. Brake cleaner is likely one of the most used products in a pro shop. It is used not just to clean brake components and prevent brake squeal but also to clean spilled liquids like brake fluid, oil grease. The cleaner is an aerosol and is powerful enough flush grit from components. Picture links to Amazon.com.
A head-mounted lamp is like having a third hand a real advantage when you are doing battle. This rechargeable LEd head-mounted lamp is conveniently sold and delivered by Amazon.com.