Spongy Brakes After Bleeding (100% Fix)


Spongy brake pedal after a brake bleed is frustrating but you’re in the right place and we’ll get to the bottom of it in this post.

Spongy brakes after bleeding? The most common cause of spongy brakes after bleeding, is contaminated brake fluid. Usual contaminates include air or moisture in the system. Most common causes, include:

  1. Brake bleeding technique
  2. Contaminated brake fluid
  3. System leak

Your correct to bleed the brakes, the most likely cause of the soft pedal is trapped air inside the hydraulic brake fluid system. If you’ve previously done some work like replaced brake pads or rotors, its common to lose confidence in the brakes.

The pedal will feel soft and ineffective until the pads and rotors bed in (surfaces mate). This is normal and test driving and braking lightly will solve the poor pedal feel. Opening the bleed nipple to push home the caliper piston is a preferred method for some when fitting pads, in so doing it is possible to allow air into the system.

If you used this technique or you’ve replaced brake lines or hoses then you likely have air in the system. Bleeding the brakes using the vacuum method below will fix the problem.

In this post you’ll learn about the three most common causes of spongy brakes and what you can do to fix them. I understand you have bled the brakes and they are still soft, so it makes good sense to eliminate a brake bleeding procedure error first.

1 Brake Bleeding Techniques

BRAKE BLEEDING SEQUENCE

Bleeding the brakes isn’t a job you do every day or may be you’ve never done it before so it’s worth checking your technique. Bleeding the brakes successfully isn’t a complex procedure but like lots of jobs requires nailing some crucial steps.

Bleeding is as you know a process where by we purge the hydraulic system of trapped pockets of air. Trapped air is compressible and that’s what causes the horrible spongy pedal feel. The process requires different steps depending on the brake bleed method employed. I prefer the vacuum brake bleed kit, but we’ll cover the 3 most common DIY techniques used.

If you’ve replaced the brake calipers recently and the brakes won’t bleed, you may find the post useful “Brakes won’t bleed”.

Vacuum Method

The vacuum method as its name suggests uses vacuum to pull brake fluid through the lines releasing trapped air. The process is simple, convenient and is a one man job.

This is my preferred method to nail it, but you’ll need a brake bleeder. I like this model, I was surprised at the price. It’s not professional grade but it is close. The Capri Vacuum Brake Bleeder is conveniently sold and delivered by Amazon. Note, this bleeder will require access to a hobby compressor.

Tools you’ll need:

  • Fresh fluid
  • Wrenches 8, 10 or 11mm usually
  • Brake bleeding kit

The process looks like this:

  • Remove, set cap aside and top up fluid reservoir.
  • Starting at the brake line farthest from the brake reservoir, attach the clear vacuum bleeding hose to the brake caliper or wheel cylinder bleed nipple.
  • Open the bleed nipple and apply vacuum to the system.
  • Check and top up fluid reservoir regularly.
  • When the hose runs free from air, close the bleed nipple while under vacuum.
  • Move to each brake line and repeat, finishing with the brake line closest to the fluid reservoir.

Gravity Method

This is my least preferred method, it’s usually successful but some systems may require a few pumps of the brake pedal to move things along. This method is a little different to the vacuum method.

Tools you’ll need:

  • Fresh fluid
  • Wrenches 8, 10 or 11mm usually
  • Brake bleeding bottle and clear hose

The process looks like this:

  • Remove, set cap aside and top up fluid reservoir.
  • Quarter fill the bottle with fresh fluid, and submerge the bottom of the hose below the fluid (important)
  • Starting at the brake line farthest from the brake reservoir, attach the clear bleeding hose to the brake caliper or wheel cylinder bleed nipple.
  • Open the bleed nipple and allow the fluid to gravity bleed.
  • Check and top up fluid reservoir regularly.
  • When the hose runs free from air, close the bleed nipple.
  • A variation on this method includes pumping the brake pedal to move the fluid through the brake lines.
  • Move to each brake line and repeat, finishing with the brake line closest to the fluid reservoir.

This is my least preferred method as the true gravity bleed technique takes longer and pumping the brakes risks damaging the seals of the master cylinder (higher risk on older cars).

Pump & Release Method

This is how my father thought me to bleed brakes, as a kid I was the brake man and my job was to pump and hold the brake pedal when instructed. This is a two person procedure, one person to build brake system pressure (brake person) and the second person releases the the fluid (release person).

Brake bleeding procedure

To execute this procedure you’ll need:

  • 2 People
  • Fresh fluid
  • Wrench’s 8, 10 or 11mm usually
  • Fluid bottle and clear hose

The process looks like this:

  • Remove, set cap aside and top up fluid reservoir.
  • Quarter fill the bottle with fresh fluid, and submerge the bottom of the hose below the fluid (important)
  • Starting at the brake line farthest from the brake reservoir, attach the clear bleeding hose to the brake caliper or wheel cylinder bleed nipple.
  • Brake man is instructed to pump brakes several times and to then hold the brake pedal down. (important)
  • The release man then opens the bleed nipple and releases the fluid pressure together with the trapped air.
  • Release man then closes the bleed nipple and repeats the process until the fluid runs without air in the hose.
  • Check and top up fluid reservoir regularly during the process.
  • Move to each brake line and repeat, finishing with the brake line closest to the fluid reservoir.

This technique isn’t advised for older vehicles, especially those that haven’t had regular fluid maintenance. This type process requires the brake pedal to go to the floor several times. This runs a real risk of damaging the master cylinder seals. Older brake systems may develop corrosion on the piston plunger and running a corroded plunger past it’s normal travel distance can damage master cylinder seals.

2 Contaminated Fluid

Brake fluid

Brake fluid quantity is important but so too is the quality. Hydraulic brake fluid is hygroscopic (attracts moisture) and that’s a problem. When a car breaks it turns that kinetic energy into heat energy at the brake rotors.

The brake caliper positioned over the rotor naturally causes the brake fluid inside the brake caliper to heat, this isn’t a problem when the fluid is fresh. However, when the fluid is old the moisture content boils and turns to steam. Steam isn’t compressible and so the pedal sinks to the floor.

Symptoms: This is generally only a problem when the brakes have been warmed up for a while and usually isn’t isn’t an issue when cold.

The fix: Replace the brake fluid. Brake fluid isn’t drained like you drain motor oil, instead the old fluid is replaced by repeating the brake bleed technique. Approx one quart (litre) of brake fluid is enough to flush the system completely.

I recommend buying a vacuum brake bleed kit, it makes the job simple and mess free. Your brake fluid should be changed every three years and the fluid marked on the reservoir cap is the recommended type.

Mixing DOT 5 (Silicone based) with DOT 3, 4 or 5.1 (Glycol based) is a NO No, it will damage your brake system. It is possible to mix the different spec Glycol fluids but it’s better to keep them separate. The main difference between the different spec Glycol fluids is the boiling point. The higher the DOT the higher the boiling point and a higher boiling point is better.

3 System Leak

Your hydraulic system works under pressure, a leak is very possible. If fluid can leak out then conversely air can leak in. A fluid leak is usually self evident, a wet oily patch around the brake components or lines needs to be investigated. Even the smallest leak will allow air enter the lines.

Common leak prone areas include:

  • Bleed nipples – Corrosion on the bleed nipple beveled seat prevents sealing.
  • Caliper seals – Brake caliper seals damages causing fluid leak
  • Rear wheel cylinder seals – Rear wheel cylinder seal are a common failure (only fitted to vehicles with rear drums)
  • Flexi hose unions – Corrosion on flexi to hard line unions
  • Brake lines – Corrosion
  • Brake unions – Build up of corrosion at unions common

The fix: Find and repair the source of the leak and bleed the system.

Faulty Flexi Brake Hose

Brake flexi hose

A faulty brake hose can also cause a spongy feel, it’s a lot less likely but I have replaced plenty especially on older cars. The flexible rubber brake hose fitted between the chassis and the suspension is flexible to allow for relative movement. The constant movement does take its toll and often without any visual ques.

The rubber hose may show signs of wear and tear and age or may not. The hose is constructed with an inner and outer wall, a rupture of either prevents a fluid loss. However the weakened wall allows the hose to swell and expand instead of sending fluid pressure to the brake caliper, a lot like squeezing a balloon in the middle. The swelling of the hose causes a horrible spongy soft pedal.

The Fix: Replace all brake hoses as the others will also be close to failing and bleed the system.

bRAKE FLUID CHART

Related Question

What do spongy brakes feel like? Spongy brakes feel soft and ineffective. Brake pedal travel towards the floor is excessive and the pedal will only have effect towards the end of its travel.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

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