How to Bleed Air From Disc Brake Cylinders

Bleeding the brake system is an important part of brake system maintenance. Most people think of brake bleeding as a way of removing air from the brake hydraulics if the brake pedal feels soft, but not everyone understands that bleeding the brakes every year or so will also remove abrasive contaminants and water-contaminated brake fluid from the system. This in turn will extend the life of the master cylinder and brake cylinders while also contributing to optimum brake performance. Bleeding the brakes is a relatively simple procedure that vehicle owners can easily do themselves.

Instructions

1

Park the vehicle on firm and level ground. Put the transmission in park, or if it's a manual transmission put it in first or reverse gear. Engage the parking brake. Loosen the lug nuts on the wheel on the rear passenger side about one full turn each. Jack up the corner of the vehicle and support it securely on a safety stand. Complete removing the wheel.

2

Locate the bleeder plug. This is a small bolt with a nipple in the middle, and it is normally located on the back of a drum brake, or the back or top of a disc brake caliper.

3

Spray the bleeder plug with penetrating oil and allow at least 15 minutes for the oil to work into the rust on the plug threads. Carefully attempt to loosen the plug slightly using a box-end wrench. Do not force the plug, or damage to the plug could result. If the plug remains seized then reapply penetrating oil and let it sit for a longer period before attempting again. Do not apply heat to loosen it.

4

Leave the box-end wrench on the plug and slip a length of clear tubing over the plug nipple. Put the other end of the tube in a container that is partially filled with brake fluid. Be sure the end is submersed in the brake fluid.

5

Locate the brake fluid reservoir. This is usually a semi-transparent plastic container located near the rear of the engine compartment on the driver's side. Remove the reservoir cap and empty the reservoir fluid by using a turkey baster. Discard the old fluid in accordance with local regulations. Fill the reservoir with new brake fluid that conforms with the vehicle manufacturer's specifications. Replace the reservoir cap.

6

Open the bleeder plug slowly until you see brake fluid just starting to run out through the tube. Do not open the plug too much, or air could flow backwards into the brake line. Start the car and gently depress the brake pedal a couple of times to force brake fluid together with any air and contamination out through the bleeder plug. Close the bleeder plug, taking care not to overtighten or shear the plug off the brake. Replenish the level in the brake fluid reservoir with new fluid and repeat the bleeding process until fresh fluid comes out of the plug.

7

Securely tighten the bleeder plug, again taking care not to damage the plug or shear it off. Replace the wheel and lower the car. Repeat the entire procedure on the rear driver's side brake, followed by the front passenger side brake, and finally the front driver's side brake. Adjust the brake fluid level to the full mark on the reservoir, and test the brake operation before driving the vehicle.