How to Flush Brake Fluid
In this article, we are going to delve deeper into the braking system by learning how to flush brake fluid. When driving, using the brake pedal will cause your vehicle to slow down and come to a stop. And while that seems simple enough, there is actually a lot more going on behind the scenes that we take for granted when braking.
While made up of many parts, we will be focusing here on the hydraulic portion, or the brake fluid. We will discuss why these components are important to maintain and how realistic it is to conquer a service like this with basic tools that almost all of us have at home.
The Braking System
The brake pedal is connected to a component called the master cylinder. This component takes force (the driver depressing the brake pedal) and converts it into hydraulic pressure. The brake fluid inside your vehicle’s master cylinder travels through hard steel brake lines to each wheel. Once there, it passes through a flexible rubber hose attached to the brake caliper at each wheel, it then pushes the piston inside the brake caliper, resulting in the caliper squeezing the brake pads toward the disc brake rotor.
All of which allows your vehicle to slow down and come to a safely timed stop.
It is the brake pads squeezing the rotor that transform the hydraulic pressure into heat. One way you can picture it is by thinking of when you are cold and you rub your hands together to create heat and warm them up. Same concept.
When this happens, the caliper (which is filled with brake fluid), as well as the brake pads and disc brake rotor, heat up. When the brake pedal is released and the gas pedal has been applied those components then cool off. This flow constantly happens every time the vehicle is driven.
These motions and heat cause the brake components to wear out normally and eventually fail over time. This is why it's an important idea to inspect the brake system regularly.
Depending on how much you drive your vehicle, the brake fluid should be serviced every 12 to 24 months.
How to Flush Brake Fluid
Let's go ahead and start a brake fluid flush!
First, follow all safety procedures to lift all four wheels of the vehicle of the ground.
With the vehicle in the air on jack stands, using a 21mm socket and an electric or pneumatic impact gun lets remove the lug nuts on all four wheels.* This will give us access to the brake calipers.*
* Your particular vehicle may use 17mm, 19mm or even 22mm lug nuts. An example of such is Toyota, which uses a 21mm lug nut.
*Additionally, if you are using hand tools like a ratchet or breaker bar to remove your lug nuts, you will want to break all of your lug nuts loose prior to taking the wheels off the ground.
Release the parking brake so the rear wheels spin freely.
Open the hood of your vehicle and locate the brake master cylinder. The master cylinder for most vehicles is located on the driver's side, toward the rear of the engine bay.
Remove the master cylinder cap.
Return to the wheels and locate the bleeder valve on each caliper. They can be found towards the top of each caliper. Break the bleeder loose and then re-snug them up. The bleeding process requires the bleeders to be snug only since we will be opening and closing them frequently.
Bleeding the brakes
When bleeding the brake system you will want to start at the furthest wheel from the master cylinder (most often the right rear wheel) and work your way around until you reach its closest.
The most common size for the bleeder is 8mm, 10mm, and 3/8in. I highly recommend using a 6 point socket or a line wrench to break the bleeder screw loose. This will prevent damage to the bleeder screw.
For the bleeding process, it is easiest to use a line wrench to open and close the bleeder, but if you don't have a line wrench, a socket and ratchet will work just fine albeit slightly messier.
Grab a drip pan or a Grypmat if you must and position it under the brake caliper to catch any fluid that spills. Grab your clear plastic tubing and insert it over the bleeder to catch the fluid. The other end of the tube into a clear plastic bottle (any disposable water bottle will do).
Bleeding Brakes with Assistance
With your wrench on the bleeder and the plastic tube inserted on the bleeder have your assistant in the driver's seat press the brake pedal and hold pressure.
Open the bleeder valve. Your buddy's foot should follow with the brake pedal all the way to the floor. This will push the brake fluid out of the caliper into our collecting reciprocal.
Next, close the bleeder valve and then have your buddy release the brake pedal.*
*This process requires good communication. This is the easiest way I have found to accomplish this task;
- You say, "Down."
- Footman confirms the command by repeating “Down" and holds the brake pedal down.
- You release the bleeder allowing fluid to leave the caliper.
- Footman should notice brake pedal that can be easily pushed to the floor. Follow the pedal to the floor and hold pressure.
- Footman says "Floor" when the pedal stops.
- You close the bleeder valve and says "Up."
- Footman removes foot from the brake pedal and confirms command by saying "Up."
This process will be repeated several times per wheel.
Every 3-4 rounds make sure to stop and check the level of the master cylinder. Don't let the level fall below half full or you may suck air into the system.
Now while sucking air into the system isn't the end of the world, if it does happen, it just means you will have to continue to bleed the system until all the air is out.
As the fluid leaves the caliper, take note of the color and how dirty it is. What you're looking for is for the fluid to begin to pass through clean. When you see fresh fluid leaving the caliper, that wheel is done and we can move on to the next wheel.
* The first wheel typically takes the longest due to its location being furthest from the master cylinder.
With the right rear wheel now bled, we can move to the left rear wheel, then front right wheel, and finally, the front left wheel. Simply repeat the above steps for each wheel.
When the bleeding process is complete, tighten down each bleeder valve. Snug it down until it stops moving and give it an additional ¼ turn to ensure they are tight.
It's a small screw that only requires about 14 ft-lbs of force, so be sure not to overtighten this screw or it can break.
After all four calipers of the vehicle have been bled, top off the brake fluid and press the brake pedal a few times to ensure you have a solid pedal.
Now go ahead and start the vehicle and check for a solid pedal one more time. If the pedal feels nice and firm, you are done. If the pedal starts to fall or fade to the floor, more bleeding may be necessary. Just start from the furthest wheel and repeat the process until the pedal is firm.
Bleeding Brakes Alone
If you don't have a buddy to assist you with bleeding your brakes, there are two other recommendations that can be performed yourself as well.
First, you can purchase a hand-activated brake fluid vacuum pump from a local parts store or Amazon.
These brake vacuum pumps come with various types of adapters, clear tubing, and a special container to catch brake fluid. With the vacuum pump in one hand, you will have a tube that goes from the pump to the holding container and another tube that goes from the container to the bleeder valve.
With the vacuum pump attached, you can simply open the bleeder valve and activate the vacuum pump.
As you pump the device you create a vacuum that sucks the fluid from the caliper. Follow the same steps as above and continue to bleed until the fluid becomes clean.
You will need to periodically stop and empty the container for the vacuum pump as well as keep the brake master cylinder full of clean fluid.
The second option is to grab yourself a plastic water bottle and some duct tape. Duct tape is always the answer!
Take a small piece of duct tape and roll it over itself so you have a sticky side on the top and the bottom. Use this to secure the water bottle to the ground under the caliper.
Attach the clear tubing to the bleeder valve and insert the other end into the bottom of the bottle. Fill the bottle with some brake fluid until the bottom of the tube is submerged. Open the bleeder valve and walk around to the driver's seat and press the brake pedal to the floor and release it.
Do this 2-3 times then go back to the caliper and check that dirty fluid is coming out. Once you see clean fluid you can move on to the next wheel. Of course, don't forget to keep that brake master cylinder fluid level full.
Keeping the tube in the brake fluid of the water bottle will allow you to pump the pedal without sucking air into the bleeder valve.*
*This last method will get the job done, but the preferred method on how to flush brake fluid is with assistance. It's my preferred method because it's the quickest and most efficient way to bleed the brakes.
There are also fancy and high priced machines that can also get the job done, but those are usually found primarily in dealerships or other high volume automotive shops that supply "shop tools" for their technicians. You don’t need them!
And there we go! Your brakes are bled. You have a nice firm pedal. Lets put those tires back on and get the lug nuts on snug. Use your floor jack to lift the vehicle, remove those safety jack stands, and lower the vehicle to the ground.
Check the vehicle's owner's manual for the exact torque spec required for your lug nuts. If you can't find the spec, it is recommended to use 100 ft-lbs of torque spec to secure the lug nuts. This will ensure that the tires are confidently installed without doing damage to the wheel studs.
Without a torque wrench, you will need to tighten each lug nut by hand until they are nice and snug then apply ¼ to ⅓ of a turn of force. Once complete, take your vehicle for a test drive to your nearest local shop and ask if they could torque the vehicle’s lug nuts.
It is normally a quick service that can be done for free but I always like to hand the tech a few bucks for his time. He will greatly appreciate it and remember you if you need his/her assistance in the future.