Brake System Bleed and Flush Guide

Got a spongy brake pedal? Did you do a pad or caliper replacement and you need to bleed and flush the brake system? This repair is a good idea when doing any kind of brake replacement because brake fluid becomes dirty from the pistons of the brake master, caliper and wheel cylinders rubbing against the metal housing of each component. These pistons hold pressurized fluid by using rubber seals that can withstand the chemical properties of the fluid.

Hydraulic pistons slide inside the housing when the brake pedal is pressed down and are held in place by the housing bore hence the metal on metal wear. This wear will cause leaks due to scores in the housing bore which the seal cup cannot seal against therefore causing a leak. A fluid change also removes moisture and contaminants which cause rust pits in the housing bores which also lead to leak failures.

This fluid is subject to extreme pressure and heat, the boiling point of the fluid is much higher then normal fluids of its kind which is important for different applications, higher boiling points (severe duty) and anti-lock braking ABS systems which require a high quality fluid, these ratings are:

  • DOT2
  • DOT3
  • DOT4
  • DOT5

Distinctive ratings define the chemicals in which the fluids are produced from such as mineral oil, ester glycol and synthetic oils. Many of these fluids are not compatible, make sure to add and flush your brake system with the manufacturers recommended fluid.

Avoid accidental fluid spillage, because it is corrosive. If you do accidentally have a spill clean it up with soap and water quickly. Always add fluid from a sealed container to avoid dirt and moisture contamination.

Here is a list of brake repairs or replacements that warrant a bleed or flush.

  • Master cylinder
  • Caliper
  • Flex Hose
  • Metal line
  • ABS valve
  • Wheel cylinder
  • Proportioning valve
  • Pads

I have created this guide to show you how you can do it yourself without using a fancy power bleeder and saving you from going to a repair garage.

I will go over this problem in detail further down in the article and how to complete this service. Watch the following video and then read through the following article to gain additional added information, though appearances may vary, the procedure is the same on most vehicles.

Let's get started

Tools and Supplies Needed

  • Small wrench set
  • Socket set
  • Vacuum hose
  • Brake fluid
  • Protective clothing and gloves
  • Shop towels
  • Helper person

Start with the vehicle on level ground, engine off, lifted safely using jack stands.

Also See: Lift and jack up your car safely

Step 1

Locate and identify the brake master cylinder fluid reservoir, fluid cap, lines, and fluid level sensor. Check the master cylinder for leaks between the master and brake power booster using a flashlight and a small mirror which is a sign of component failure. This is a sign the seals inside the master have failed and there is no reason to continue this procedure until the master has been replaced. If no leaks are present continue with this guide.

Step 2

Before opening the master cylinder cap use a shop towel to wipe it clean. This will help keep dirt out of the reservoir which can cause seal failure by contaminating the fluid.

Step 3

Next, grasp the lid and twist it counterclockwise to remove while gently lifting it upward. Some caps have a fluid level sensor which is will have wires attached to it, simply wipe off any excess fluid and set it off to the side.

Step 4

If a screen is present in the reservoir remove it with a twisting motion then insert a suction device which most of you have in the kitchen (turkey juice remover). Have a small plastic container to release the old fluid into to discard. Avoid spillage if you can and rinse with water if an accidental spill occurs. Some reservoirs are designed with a dual chamber, a small hose will need to be attached to the suction device get over the divider in the middle of the reservoir.

Try to get as much fluid out as possible as to not contaminate the new fluid. If all the fluid cannot be removed it will mix with the new fluid and most of it will be flushed out when the process begins.

Step 5

Then, carefully pour the new fluid into the reservoir, you may need to use a funnel to aid in this process. Continue adding until the fluid reaches the full line and then remove the funnel. Most systems use a DOT 3 or 4 fluid but if you are not sure consult your vehicles owners manual.

Step 6

Wipe off an access fluid then reinstall the reservoir cap.

Step 7

Locate all four brake fluid bleeder fittings located near the top of each caliper or wheel cylinder which may have a dust cap over them. The system bleeder screw can be fairly tight because bleeder screws seals against a taper fit seat in the valve. When loosening apply WD40 or equivalent to aid in rust removal, use a 6 point wrench or socket is best to avoid rounding.

Step 8

Using a small screwdriver or pick remove the bleeder dust cap. Place it to the side to be reinstalled, do not discard.

Step 9

Then place a boxed end wrench and rubber hose positioned onto and over the bleeder. A rubber hose is helpful to avoid fluid contamination from getting onto the pads or shoes, access fluid should be hosed off with water once the job is completed.

Step 10

Now it's time to start the bleeding process, start with the right rear and then the left rear, then head to the front and do the right front and then finish with the left front. Open the first bleeder valve while the opposite end of the rubber tube is in a fluid catch container.

Step 11

Have a helper push down on the brake pedal slowly and hold even pressure downward.

Step 12

Fluid will then start to flow out of the bleeder or tube. Air bubbles will be in with the fluid stream if air is present in the system.

Step 13

As the fluid flow slows down tighten the bleeder valve while maintaining pressure on the pedal. Do not allow the pedal to come upward while the valve is open or it will such air back into the system and then you will need to start the bleeding process all over again.

Never pump the brake pedal as this will cause additional air to get into the system. There is a very small orifice inside of the master cylinder that allows fluid down into the fluid chamber, pumping the pedal cause's air to be sucked in through the seals of the master creating more problems.

Step 14

Once the bleeder valve is closed, allow the brake pedal to slowly return to its normal position. While servicing each wheel observe brake fluid level in the reservoir and refill as needed. Continue this process at each wheel until clean fluid is present with no air bubbles being expelled from the bleeder valve or hose.

Step 15

Add additional fluid to the reservoir to keep the master full. Do not allow the fluid to become empty or air will be pumped into the system.

Step16

Refill the fluid to the full line of the reservoir and reinstall the lid.

Step 17

Using a shop towel wipe any spilled fluid and rinse with water if needed. Then start the engine and check brake pedal operation which should be firm toward the top of its travel. If the pedal is on the floor or spongy there is air still in the system. This means the brake shoes are out of adjustment, the master cylinder is bypassing internally or the system has a leak.

Also See: Brake pedal goes to the floor

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Article first published