Brake bleeding sequence; right rear, left rear, right front and then left front

Brake bleeding is necessary when a system has been opened or the brake fluid has been allowed to get too low in the master cylinder. Air can enter due to a low master cylinder caused from a leaky wheel cylinder or other brake component. If a hydraulic part like a wheel cylinder, caliper or brake line has been replaced the system will need to be bled. Brake bleeding at the wheels can be done several different ways. The most common way is old fashioned manual brake bleeding. 

It’s when an assistant pumps the brake pedal up and holds pressure while the bleeder screws are opened at the wheels letting air escape. When the fluid streams out without any air and the pedal is firm the job is done.

Manual Brake Bleeding

Manual brake bleeding as stated above involves two people working together. The master cylinder must be kept full during the entire process or air may re-enter the system. While the assistant applies pressure to the brake pedal, start with the wheel that is farthest away from the master cylinder. Open the the bleeder screw allowing fluid and air to stream out. The assistant must keep the pedal down until the bleeder screw is closed. Then the process is repeated several times at each wheel until all the air has been bled out, be sure to keep the fluid level up in the master cylinder during this process.

 But, did you know that this job can be done by ONE person reducing the time and trouble involved? Gravity or Vacuum bleeding makes this possible, read on for more info.

Gravity Bleeding

Gravity bleeding can be done by ONE person. The fluid in the master cylinder is naturally at a higher point than the bleeder screws at the wheels. So gravity will pull the fluid slowly down when the bleeder screws are opened. The process can be sped up a little by lightly pumping the brake pedal while when the bleeder screws are opened (avoid pushing the pedal all the way to the floor). All bleeder screws at the wheels can be opened at once. Like manual brake bleeding, the brake fluid in the master cylinder needs to be kept from going empty or air will enter the system. The bleeder screw farthest wheel from the master cylinder should be closed first.

Vacuum Bleeding

Vacuum bleeding is done in the same sequence as manual brake bleeding. The advantages of using a vacuum brake bleeder like a Vacula brake bleeder is that it saves time and is done with less mess. Vacuum brake bleeders (not the hand pump type) use shop air to create a venturi vacuum that allows the fluid to be drawn out through the bleeder screws quickly. The tube from the vacuum brake bleeder is attached to the bleeder screw and the screw is then opened. The clear tube makes it easy to see when straight fluid with no air is being drawn out.

Hydraulic Clutch Bleeding

One of the hardest hydraulic systems to bleed can be clutch master and slave cylinders. Many times manual bleeding or gravity bleeding cannot remove the air from these systems. On more than one occasion during my time as a technician, my vacuum brake bleeder has saved the day by pulling the air out of a hydraulic clutch system. It seems like the Ford Ranger and some foreign cars can have air trapped in their clutch system easily. When this happens it’s a great feeling to have a vacuum bleeder on hand that can easily remove the air from a stubborn system. 

Question: How do I bleed my master cylinder?

Answer: Bench bleeding a master cylinder is required before installing it on the car, see our master cylinder bleeding article for much more information.

Question: I’ve replaced all the brake lines on my Chevy truck, no matter how much I bleed the system the pedal sinks to the floor. What could be the problem?

Answer: It could be a bad master cylinder. But the master cylinder could just have too much air (lost it’s prime) If the brake fluid went completely empty, the master cylinder may need to be removed and bench bled, then put back on and bled at the lines and then at the wheels.

Question: After putting on new wheel cylinders, I’ve gotten all the air out of the system, but the brake pedal seems a little low. Any suggestions?

Answer:Brake pedals in different cars have different characteristics, simply put they can feel different compared to other make and models, but it could be normal for that car. If you are sure that the pedal was higher at one point ten the rear brakes may need to be adjusted to bring the pedal up (avoid over-adjusting).

Question: I just replaced the front calipers on my Explorer. Do I need to start with the rear brakes when I bleed them?

Answer:You should only have to bleed the front brakes since you only opened the system in the front. Hopefully you didn’t let the fluid go empty in the master cylinder while changing the calipers or it will be harder to bleed. Also you may want to bleed the rear too, not because of air but to replace the fluid for regular maintenance.

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