Introduction: How to Flush Brake Fluid Using a Pressure Bleeder

By 4DIYers
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Tutorial on how to flush your vehicle’s brake fluid using a pressure bleeder. Here I am working with a 2007 Volvo C30. There is usually specific maintenance intervals for brake fluid and this information can be found in your vehicle’s owner’s manual. Some vehicles may require a replacement at every 30,000km/20,000 miles or every 2 years. Other vehicles may have a longer maintenance interval such as 160,000km/100,000 miles or every 10 years. Brake is a type of oil that is hygroscopic, meaning it’s able to absorb moisture which is present in the air, either through leaks, seals, or even when the cap is off the reservoir. Each type of brake fluid has a boiling point rating and each is effected differently based on moisture content. Excessive moisture can cause premature failure of components, as well as poor braking performance. Heat can break down the fluid, including these additives which will cause poor braking performance and even premature failure of components. Old fluid can also cause a spongy pedal feel and increase the chance of brake fade under heavier braking.

Tools/Supplies Needed:

  • wrenches
  • about 10 inches of clear rubber hose
  • clean rags
  • brake fluid
  • pressure bleeder
  • vacuum pump or turkey baster
  • jack
  • jack stand
  • wheel wrench

Step 1: Fluid Requirements

Start by opening the hood and locating your master cylinder reservoir. Use a clean rag to wipe the surrounding area of the cap to prevent any foreign contaminants entering the reservoir.

In order to determine which type of fluid is required for your vehicle, this can be printed on the top of the reservoir cap. You can also refer to your vehicle’s owner’s manual under a fluid type of capacity section. Along with type, we’ll need to know the capacity required for the vehicle. You should have about 0.5L more of brake fluid, for this vehicle is requires 0.6L and I have 1L which should be plenty.

In the last photo, you can also see the comparison between the old and new fluid.

Step 2: Pressure Bleeder Kit

Here is the pressure bleeder kit which not only allows you to bleed or flush your brake fluid, but also work with other vehicle fluids which I’ll be saving for future vehicles. The tank can hold up to 3 litres of fluid and is pressurized using the pump on the top. The orange cap serves two purposes, one is a fill point and the other is a spring loaded valve to relief the pressure. The pressure gauge allows us to keep an eye on the pressure to ensure there is no leaks or so we can see there is always pressure. With the power bleeder this can be operated by one person, is typically the fastest compared to any other bleeding method, and allows you to pressurize the system with minimal risk of air entering the system.

The kit comes with a generic style caps to be used on any type of master cylinder reservoir or in this case we can also use a cap which is a standardized style for European vehicles. And finally there is the feeder line, the black threaded fitting connects to the pressure bleeder and the other end which includes a valve and quick disconnect attached to the master cylinder cap.

Step 3: Installing the Reservoir Cap

Usually you can use a turkey baster or vacuum pump to remove a majority of the old fluid in the reservoir, however some of these reservoirs can have an irregular design or include baffles making this difficult. So we can skip this method and it will require slightly more fluid removal at the first bleeder unit we start seeing clean fluid.

For this car, I am using the supplied European style cap. Screw that into place and ensure it’s tight.

As another example using the generic clamp on cap. Again ensuring the reservoir is clean. Put the top cap into place. It has a rubber base which is able to compress and seal against the opening. Pull the chain around the bottom side, loop it onto the hook, that hook should be backed off as far as possible, and then tighten that hook.

Step 4: Connecting & Checking for Leaks

Screw the line onto the tank. This kit has a particular great design as the tank side fitting allows for rotation, therefore preventing twisting of the feeder line. The quick disconnect side allows for the same type of rotation as well.

Ensure that valve is turned perpendicular to the line, this will mean it’s turned off. Pump the system up to about 15psi and monitor the gauge for a pressure drop. If there is a pressure drop, you have a leak and any connections will need to be inspected and tightened accordingly. This allows us to check for any leaks between the valve of the line and pressure tank.

Open the valve slowly, it should be parallel with the feeder line. You’ll see the gauge drop about 1psi and again monitor for a leak. We can somewhat centralize a leak if there is one, if the pressure drops here then we have a pressure leak past the quick disconnect.

Once you have verified there is no leaks, release the pressure by pressing the pressure relief valve. Disconnect the line and then fill the tank.

Step 5: Filling & Reconnecting the Pressure Bleeder

As mentioned earlier, the orange cap which has the pressure relief valve is also the fill point. The tank should have enough fluid so it doesn’t run empty and risk the chance of introducing air into the system. The tank will have the full 1L of brake fluid. There is usually specific maintenance intervals for brake fluid and this information can be found in your vehicle’s owner’s manual. Some vehicles may require a replacement at every 30,000km/20,000 miles or every 2 years. Other vehicles may have a longer maintenance interval such as 160,000km/100,000 miles or every 10 years.

Reinstall that cap, make sure it’s hand tight and then reinstall the feed line going directly to the vehicle.

Pump the system up to about 15psi. Pressure requirements may vary between vehicles, if you exceed a manufacturer’s pressure limit this may damage internal seals within the braking system. Monitor the gauge for any pressure drops which would indicate a leak. If a pressure drop is present, it will need to be fixed. Some vehicles also have different bleed procedures, such as bleeding the closest wheel to the master cylinder, while others require bleeding the furthest wheel first that tends to be the most common.

Step 6: Furthest Wheel First

For this vehicle I am starting with the furthest wheel first. Jack the vehicle up. Sometimes you can take a quicker methods by just gaining access to the rear of the wheel if you have access to a hoist or a vehicle with high ground clearance.

As a safety precaution, use a jack stand as well.

This car has four wheel disc brakes, so we will be working with calipers on the rear. Locate the bleeder screw which will be covered by a rubber cap. Clean any dirt off with a rag, remove the cap and clean again. For this car, it has 10mm bleeder screws on the rear. Using the box end of the wrench, this will prevent any slippage and stripped the bleeder. You’ll need a clear rubber line that fits tightly on the bleeder to direct the old fluid into a container. Here I’m using a clear water bottle so you can see the fluid color.

Since we have that pressure bleeder already pressurized, loosen the bleeder and watch the fluid flow. The furthest wheel will be draining the most amount of fluid as it’s the furthest distance and it’s also remove any old fluid from the reservoir too. The pressurized reservoir pushed the old fluid through the system while topping up with free fluid and not allowing air to enter in the system. This water bottle holds 500ml of water, so we should be looking at roughly 250ml of fluid from this wheel including the reservoir. If you remove more, this is fine and just means the system is thoroughly flushed.

Wait until clean fluid is present in the clear rubber hose, then tighten the bleeder and remove the line. Be extremely careful with brake fluid, it can damage paint. The furthest wheel will require about 40% of fluid extraction, this does vary between vehicles and this is just a rough estimate.

Reinstall the wheel and move onto the next furthest wheel which is the driver’s side rear. Against using the same procedure, jack up the vehicle, remove the wheel and used a jack stand.

Step 7: Moving Onto the Next Wheel

Locating the bleeder screw, remove the cap, install the box end of the wrench, and then install the rubber line. If you find the fluid comes slow out of the bleeder, this could either be from a dirty hole in the bleeder or just simply the design.

Brake is hygroscopic, meaning it’s able to absorb moisture which is present in the air, either through leaks, seals, or even when the cap is off the reservoir. Each type of brake fluid has a boiling point rating and each is effected differently based on moisture content. As an example, DOT 3 brake fluid has a boil point of just over 400 degrees
Fahrenheit, but this varies between manufacturers. If moisture content is measured at 3%, this drops the boiling point down to about the DOT minimum requirement of 284 degrees Fahrenheit. Furthermore, brake fluids also have additives to prevent corrosion, foaming, viscosity stabilizers, acid neutralizers, etc that ensures your braking system has a long life. Heat can break down the fluid, including these additives which will cause poor braking performance and even premature failure of components. Old fluid can also cause a spongy pedal feel and increase the chance of brake fade under heavier braking.

Once clean fluid is present in the hose, tighten the bleeder. This time around roughly 30% of the fluid would have been removed from the total system’s capacity. Reinstall the wheel and now we’ll be moving onto the second last wheel.

Step 8: Second Last Wheel

This time it’s the front passenger side. As you get closer to the master cylinder, less fluid will need to be removed as the lines are shorter.

It’s import to periodically check the pressure bleeders gauge so the pressure rating doesn’t drop to a low value, otherwise we an risk introducing air into the system. Personally I prefer to keep the pressure between 10-15 psi. For each wheel, you may see a pressure drop of 2psi at the very most with the furthest wheel. As you get close to the master cylinder, the pressure drop will become less.

The front bleeder screws on the calipers are a different size on this vehicle, so we’ll need a 9mm instead. Install the wrench, then the rubber hose, and ensure you have that catch container or bottle in place.

Crack the bleeder and drain the fluid until clean fluid is present in the line.

Tighten the bleeder, remove the hose, again being careful not to get brake fluid on the paint. I normally like to wipe away any residue from the bleeder, this will help spot a leak if one occurs. Here, roughly 20% of the total system’s fluid should have been removed.

Reinstall the dust cap. If these caps are missing or damaged, then they should be replaced. Reinstall the wheel and finally we’re onto the last wheel.

Step 9: Last Wheel

If these dust caps are stuck in place, try to rotate them slightly to help break them free. Use a rag to clean up any debris around the bleeder screw. Install the wrench and then the clear rubber line, along with the catch bottle. Crack that bleeder and watch the fluid flow. This caliper, considering it’s the closest to the reservoir will require the least amount of fluid to be drained, so roughly 10% of the entire system.

Eventually you’ll see the new clean fluid present in the line, the bleeder can then be tightened. Remove the line and wrench. Wipe off any residue on the bleeder, then reinstall the cap.

And finally reinstall the wheel.

Step 10: Remove the Pressure Bleeder

Once done, there was about 100ml of fluid remaining in the pressure bleeder. Release the pressure by pressing the relief valve. Towards the end of the pressure I also gave the line a light giggle to remove any fluid which my drip once the line is removed.

Close off the valve and then disconnect the line at the reservoir cap. It’s important not to leave the reservoir exposed to air long, as mentioned earlier the brake fluid will absorb moisture. Clean off the cap to remove any contaminants which could be present and then install.

The pressure bleeder does an excellent job maintaining the level of the fluid in the reservoir, as you can see we are between the minimum and maximum markings. If there is too much fluid, then will need to be removed using a turkey baster or vacuum pump. If the fluid is low, then add accordingly.

Step 11: Check the Brake Pedal Feel

Start the vehicle and check the pedal feel. We should have a firm pedal feel with no sponginess. If you have a spongy pedal, then air maybe present in the system and the procedure should be repeated to remove the air.

Step 12: The Comparison Between the Old & New Brake Fluid

And here is a comparison between the old and new fluid. As you can see the old fluid on the right is slightly darker in color and is somewhat murky. Due to no previous maintenance records for this vehicle, it’s hard to say when this fluid was last replaced. As for testing the moisture content in brake fluid, I do have a video on this so be sure to check it out.

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