Jump LinksOperation ExplainedBrake Fluid TypesStep One: Fluid LevelStep Two: Gravity BleedStep Three: Pressure BleedStep Four: Check For A Good PedalStep Five: Clean Up!Bleeding The ABS ModuleA vehicle's brake system takes some serious abuse, can generate a ton of heat, and requires regular maintenance for the best performance. Brake fluid flushing for maintenance or after a brake component replacement is critical to the overall health and proper operation of the brakes. However, once the otherwise sealed hydraulic brake system is opened for maintenance and repairs, it must be bled of any air before you'll have a nice firm brake pedal again.Bleeding brakes can be a big job, especially on late model vehicles like the BMW X5, requiring the use of a scan tool to fully deplete the braking system from air pockets. Listed below are the steps on how to bleed brakes, achieve a firm brake pedal and regain the most stopping power from your vehicles brake system.A vehicle's brake system is a highly complex system that deals with vehicle control and the safety of vehicle occupants. It's highly recommended to have your vehicle inspected and serviced by a properly trained automotive technician. Always wear correct PPE, as brake fluid can be harmful to eyes and skin. Under Pressure: Contemporary Brake Systems Operation Explained Centric The braking system of a car has a big job. It all starts with the brake pedal and its interaction with the master cylinder when pressed. The job of the master cylinder is to provide hydraulic pressure to the brake calipers (or wheel cylinders on vehicles equipped with drum brakes) during braking. When you press the brake pedal to slow down or stop your vehicle, a complex series of events takes place. When the brake pedal is pressed, a rod pushes on a piston or primary cup inside the master cylinder. When the primary cup inside the master cylinder is acted upon, it compresses brake fluid, pushing it through small ports or passages in the master cylinder.At the same time, fluid from a reservoir fills the master cylinder through a compensating port. Brake fluid makes its way through the entirety of the brake system, passing through steel lines, proportioning valves and rubber flex hoses. The brake system is a closed or sealed hydraulic system. This means that all brake lines, hoses and valves are constantly filled with brake fluid, leaving no room for anything like air or water. Once pressure has reached the calipers and/or wheel cylinders, the braking action takes place. Since fluid does not compress, the braking action is immediate; we don't have to wait for brake fluid to travel from the master cylinder to calipers or wheel cylinders - we just have to apply the pressure via the brake pedal. Brake Fluid Types Aaron Bersée/CarBuzz/Valnet Besides all the hard parts and computers that comprise a braking system in a late model car, no stopping would happen without the lifeblood of a brake system - the brake fluid. Before the brake bleeding procedure begins, it's crucial to know what fluid your brake system requires. Like engine oil, different versions of brake fluid are applicable to different systems. As a braking system is hydraulic, the fluid is not only a key component of the process, but must be able to withstand the harsh conditions of its environment.As the brake system is not isolated from the elements, brake fluid must maintain fluidity at low temperatures, it must be resistant to corrosion (as much as possible), it must be compatible with rubber seals and hoses, and it must resist boiling at extremely high temperatures. These criteria were established and are maintained by the U.S. Department of Transportation and the NHTSA. Always check to make sure that you're using the correct fluid; Most vehicles of a similar era will share the same fluid, with some fluids even being interchangeable.*Fahrenheit, indicates dry boiling point. How To Bleed Brakes: A Step-By-Step Guide Stellantis Step One: Fluid Level Before bleeding the brakes, it is imperative that the brake fluid reservoir is topped off with brake fluid. The reservoir sits directly on top of the master cylinder. As this is a sealed system, running out of brake fluid while bleeding the system of air can introduce more air into the master cylinder and the lines. This fluid level should be monitored closely throughout the procedure. Step Two: Gravity Bleed There are two ways to begin this procedure. Some technicians prefer to begin the process with what is called a gravity bleed. This step is helpful but, sometimes, not effective and not mandatory. With the cap off of the brake fluid reservoir, open all four bleeders, starting with the one that is furthest away from the master cylinder, typically at the rear right wheel. At this point, it's a waiting game. The idea of the gravity bleed method is just to get fluid to the brake bleeder. With the bleeders open and cap off the reservoir, brake fluid is eventually able to make its way through the brake system and to the bleeder, pushing out much of the air that is trapped in the brake lines.You will know the gravity method has worked once you start to see brake fluid dripping from some or all of the bleeders. At this point, you can close the bleeders. Check the brake fluid level in the fluid reservoir and add as needed. Gravity bleeding is not intended to be a final step, it simply gets the brake system primed for a proper pressurized brake bleeding procedure. Step Three: Pressure Bleed CarBuzz/Valnet To properly bleed the brakes using pressure, you'll need an assistant to pump the brake pedal while you release brake pressure from the system using the bleeders. Starting again from the furthest point from the master cylinder, have your assistance pump the brake pedal several times, and hold the brake pedal down after the last pump. Make sure to keep the brake pedal depressed, as it is crucial to the success of the brake bleeding procedure. This crucial step ensures that the pressure in the lines and the bleeder remain constant, not allowing any air back into the system once the bleeder is opened. Once it's been established that the brake pedal is firmly pressed down, it is safe to open the bleeder. At this point, both air and brake fluid should be observed (visibly or audibly) exiting the bleeder.Your assistant should also feel the pedal move towards the floor. When your assistant feels that the pedal has moved and will travel no further as if it has "bottomed out," it's safe to close the bleeder and repeat the process, working your way around the vehicle and closer to the master cylinder. Your assistant will notice two things about the brake pedal; it will start to feel firmer as you work your way around the vehicle, and it will have a longer distance to travel every time they're holding brake pressure when you open the bleeder and the pedal goes to the floor. The fluid should be closely monitored. The brakes are considered to be bled when you no longer observe air exiting the bleeder, but instead only a steady stream of brake fluid. Make sure to top off the brake fluid reservoir between each bleedign attempt. Step Four: Check For A Good Pedal Ford After all that, the brake pedal should feel firm upon the initial press, and remain that way. It should also have a minimal amount of pedal travel. If the pedal has too much travel, is too low after being pressed, or feels soft or "spongy," air still remains in the system and the procedure must be done again until the pedal feels firm and at the proper level when pressed. If the problem persists, you may have to bleed the antilock brake module, which also may require the use of a scan tool. Step Five: Clean Up! AaronBersée/CarBuzzValnet Brake fluid is corrosive and can cause damage to painted surfaces and the brake pads or shoes. It is very important to clean all the excess brake fluid off all surfaces to avoid damage or contamination of new brake linings. For best results, a non-chlorinated brake cleaning solution is recommended and readily available at auto parts stores. The Computerization Of A Brake Service Bleeding The ABS Module DB Although the mechanical method of pumping the brake pedal to remove air from the brake system is highly effective, cars equipped with anti-lock brake systems (ABS) often need more intervention to fully deplete the system of air. When air gets introduced to an otherwise sealed hydraulic system, it wants to find the highest spot within the system, many times that includes the ABS module. In many cases, a scan tool will be needed to properly perform this procedure. With so many different antilock brake systems across many different makes and models of cars and trucks, the procedure and even software for doing so vary greatly.Typically, this procedure will require at minimum a bidirectional scan tool with ABS-specific software/capabilities. Manufactures have different protocols for the bleeding procedure and scan tools have propietary software and user interfaces to navigate for a successful bleed. Check with the manufacturer or owners manual for explicit instructions or take the vehicle to a professional repair facility that has the proper equipment to bleed the system for best results.