To do this flush, we open the brake lines located at each wheel and allow the brake fluid from the brake master cylinder to "gravity bleed" as we continue to feed new fluid to the master cylinder until the fluid runs clear at all wheels. By gravity bleed I mean without the assistance of anything other than allowing the fluid to slowly drip from the lines by the natural force of gravity.

You are probably familiar with the term "bleeding the brakes" when talking about a brake job. When the brake lines are opened or any work is performed to the brake system that can allow air to get trapped within the lines, the brakes must be bled of air. In the earlier days, the mechanic would bleed the brakes by having someone pump and hold pressure on the brake pedal as he opened the brake lines located at each wheel. This method of bleeding the brakes is not a recommended procedure for newer brake systems (discussed later).

What is the difference between flushing and bleeding? Flushing is just that, flushing the old dirty fluid out of the system and replacing it with new clean fluid. Bleeding usually consists of removing just enough brake fluid to get out the air pockets that have become trapped in the system, and usually does not focus on the time consuming process of removing the dirt and old fluid from the system.

One side note learned by experience. If you are interested in doing a brake fluid flush on your own vehicle, be warned of the potential dangers. Foremost, follow the brake bleeding procedures outlined in the repair manual you should be using. Stepping on the brake pedal with the brake lines cracked open can cause the dirt and debris to be pushed into the body of the master cylinder, thus causing damage to internal parts and seals of the master cylinder and the anti-lock brake components. Stepping on the brake pedal as someone under the vehicle opens each brake line at the wheel used to be the way you bled brakes, but not anymore.

Gravity bleeding does take a little longer to perform and can require a lot of new brake fluid to push out the old dirty fluid, but the risk of doing internal damage to the anti-lock system is greatly reduced. They also make vacuum assisted brake bleeding and flushing equipment to help speed up the process.

How can you tell if your vehicle is due for a brake fluid flush? They make special test strips which can detect high levels of moisture present in the brake fluid, but I prefer the old fashioned eye ball method personally. Remove the brake master cylinder cap and visually inspect the condition of the fluid. Brake fluid should be clear or a slight yellowish tent, so black or dark colored dirty fluid should be quite obvious even to the untrained eye.


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