Understanding Brake Bleeding

Closeup of car mechanic repairing brake padsBrake fluid is one of the most essential parts of your automobile, and any auto mechanic training will hammer that home for you. The proper changing and refilling of brake fluid regularly ensures that your brakes are working in the best condition they can be, which will greatly reduce your chances of an accident, and positively improve the safety of driving your vehicle.

To change and refill your brake fluid, you’ll first have to understand how to “bleed the brakes” in your vehicle, which is a term for emptying out the brake fluid in order to replace and refill the fluid, or to purge out bubbles that occur in the fluid, causing problems. Brake bleeding can be done in several different ways, and should be done every three to four years to ensure a properly working brake system.

Pump and Hold

This is the most common method of brake bleeding, and it can be performed with either one or two people – however, having two people ensures a much smoother and safer operation. In the two person scenario, one person pumps the brake pedal to compress the air, and then they will hold the pressure on it. Then, the other person opens the bleeder valve and lets out the fluid and air from the valve and then closes it up again after the pedal lands, preventing air being sucked back in.

A length of tubing, usually clear, is connected to the valve and run into a container to collect the brake fluid, which is extremely toxic, and so the fluid and bubbles can be viewed. The reservoir in the master cylinder needs to be replenished quite often, because if you let it go dry, the process will have to be done again.

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Vacuum Method

In the vacuum method, a specialized vacuum pump is attached to the bleeder valve and the fluid is extracted until it’s free of bubbles. Again, ensure the master cylinder reservoir level is carefully maintained. The vacuum method, while quick, is not the best and can still result in some bubbles getting back in. Find out more in this video demonstration:

Pressure Method

In this method, a specialized pressure pump is attached to cylinder and then filled up with fluid. The pump puts pressure through at about 10psi and clears the cylinder of air. In this method, one advantage is that it’s very unlikely that the reservoir will run dry.

It is recommended to have an auto mechanic perform this process, as brake fluid is corrosive and highly toxic, and if you’re unfamiliar with the process it could have dangerous consequences. Protective gear and safety precautions should always be taken when dealing with brake fluid, and having the expertise of an automotive technician is highly recommended.


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