How To Easily Master The Brake Bleeding Process.
A vehicle’s brake system must be bled anytime air is introduced into the system. If a brake line is opened air can get trapped in the circuit, causing a spongy brake pedal. Air needs to be bled out of the system to ensure the system operates properly. In this article, I’ll take the mystery out of the brake bleeding process and show you how to do this relatively simple procedure properly.
Why do brakes need to be bled?
Anytime brake work requires opening up the hydraulic system, the system needs to be bled.
An example can be if a brake caliper is replaced, or a flex hose is, anytime fluid escapes the system and air gets in, it requires bleeding of the system.
While it may not seem like a big deal, even a small amount of air trapped in the system can cause many issues including…
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- Spongy Brake Pedal: This is perhaps the most obvious issue when air is present. Air, unlike fluid, will compress. Imagine what happens when you press the brake pedal, instead of directly transferring force to the brake calipers or wheel cylinders, the pedal compresses the air in the system first, leading to a spongy or soft feeling in the pedal. This is a very unsafe situation, depending on how airbound the system is, the pedal can go to the floor and barely stop the car.
- Reduced Braking Performance: Just a little air in the braking system can be a worse situation because you may not realize there is a problem until you need to stop fast in an emergency.
Even a little air in the brake lines disrupts the smooth flow of brake fluid. This decreases the overall hydraulic pressure within the system, leading to reduced braking performance.
If you are reading this chances are you know enough about brakes to realize they need to be bled. If you are having issues getting the brake pedal feeling right, or you are just curious about how brakes are bled properly keep reading to find out the correct brake bleeding process.
How To Master The Brake Bleeding Process.
There are 3 main ways to bleed the air out of a brake system, below I will break them down.
- “Old school” pumping method: Get a helper to pump the pedal and hold it down as the bleeder screw is opened.
- Pressure bleeding: This is when you use a pressurized brake bleeder that sends pressurized brake fluid into the system via the master cylinder.
- Gravity bleeding: This is simply opening up the bleeder screw and allowing the air to escape naturally over time.
Let’s start with the tried and true… “Old school” brake bleeding.
To bleed your brakes this way you will need some help sitting in the driver’s seat. Start with ensuring the master cylinder has enough brake fluid in it and keep checking it throughout this process, if the fluid runs low you will just be pumping more air into the system with every step.
Start at the right rear wheel, the reason for this is it’s the furthest away from the master cylinder. This ensures as you move forward there is no air trapped between the master and further points in the system.
Set up properly.
Brake fluid is pretty nasty stuff, you definitely don’t want this stuff all over the car, in your eyes, or in the driveway. I recommend wearing gloves and safety glasses. As you open the bleed screws the fluid will spit out so you want to avoid letting it all over your wheels, calipers, or tires.
I have found a cheap and easy solution to keep the fluid contained and the job much cleaner listed below.
How to make your own brake bleeding container
Grab a clear empty gallon jug for washer fluid and some small silicone vacuum hose from a parts store, drill a hole in the top, and push the hose through, making sure it’s kind of snug. Then cut another cross hatch in the side near the top, this is where you can store the hose and keep fluid from dripping when you are done.
Add a flexible hook around the handle and you are done! Just place the hose on the bleeder while you open it and all of the fluid will run into the jug!
How to start the brake bleeding process.
Start at the right rear brake caliper (or wheel cylinder.) Have your helper pump the brake pedal 4-6 times and then hold the brake pedal to the floor firmly.
Place the vacuum hose of our makeshift catch over the bleeder nipple and open the bleeder slowly. You will hear (or feel) the air spitting out, keep an eye on the hose going into the jug and watch for air bubbles. This allows you to gauge how progress is going.
For your helper, the pedal will slowly drop down to the floor, be sure to have your helper let you know when the pedal is all the way down to the floor, and make sure they hold it down until you close the bleed screw. Once the bleeder is closed the brake pedal can be let back up. Make sure your helper DOES NOT let the pedal up before the screw is closed again or you will pull air into the system from the open bleeder! Some people place the end of the hose into fresh brake fluid to avoid this, however, it’s not necessary if done properly.
Repeat this same process until no air can be seen as you open the bleeder (usually 3-4 times) then close the bleeder snug and move to the next wheel. Keep going at each wheel being sure to check and top up the brake fluid level every couple of runs.
On 99% percent of cars, the correct wheel sequence for bleeding brakes is…
- Right rear
- Left rear
- Right front
- Left front
After repeating this at all 4 wheels you should have a nice firm brake pedal, if not check the system for leaks and repeat if none are found.
Pressure bleeding the brakes
When using a pressure bleeder the process is exactly the same, just without the need for a helper, the bleeder simply pushes the fluid through the system instead of your buddy pumping the pedal.
Pressure bleeding is great for flushing the entire brake system, while you bleed out the air.
What about gravity bleeding brakes?
Gravity bleeding is a process that allows air to naturally escape the system slowly.
Fill up the master cylinder and open the bleed screw at the right rear wheel, then walk away for a little while. (Usually 10-15 minutes.) Over time the natural gravity and air rising will make its way to the bleeder screws and out. Perform this in the same sequence as above. Be sure to pump the brake pedal in between the wheels to keep the lines full.
Gravity bleeding is very effective in older vehicles that don’t have ABS pumps.
This may be disputed by some but I have had awesome luck with this tactic in the past, gravity brake bleeding has even surpassed the others on some occasions.
Wrapping up the brake bleeding process
Bleeding the brakes on a car is fairly straightforward, The issue that mainly occurs is a frozen brake bleeder or a helper that lifts up the pedal too soon.
Be sure to check for any leaks after you are done and always confirm that the brake pedal feels firm and the car stops well.
