How to Flush a Contaminated Brake System

Modern automobile brakes rely on hydraulics to connect the master cylinder to the brakes on the four wheels. The hydraulic brake fluid will absorb moisture from the air and any exposure to water, and the fluid can also accumulate abrasive solid contamination from brake part wear, corrosion or outside sources. Regular bleeding of the brakes will limit the contamination buildup, but if the system becomes heavily contaminated it may become necessary to completely flush the system and replace all the brake fluid. With a little mechanical aptitude, a helper and a familiarity with the correct procedures, this is a task the DIY mechanic can handle.

Instructions

1

Park the automobile on level ground and shut off the engine. Locate the brake bleeder nuts on the vehicle's four brakes. These are small nuts with a nipple in the middle, and are normally located on the tops or backs of the brake calipers or the backs of drum brakes near the tops. Jacking up the car can make it much easier to reach the bleeder nuts on most vehicles. Be sure to set the vehicle securely on a jack stand before doing any work under the vehicle. Gently remove any rust and dirt from around the bleeder nuts, using a toothbrush or wire brush if necessary. Soak the bleeder nuts with penetrating oil, taking care to not get the oil on any other brake parts. For best results, soak the bleeder nuts the night before and allow the penetrating oil to work on the nuts overnight, and then soak the nuts again about half an hour before you plan on doing the job.

2

Place a box wrench or flare-nut wrench over the bleeder nut of the rear, passenger side brake, and then slip a length of clear vinyl tubing onto the nut nipple. Place the other end of the tubing into a clear plastic container set securely on the ground.

3

Open the hood and locate the brake fluid reservoir. It is a semi-clear plastic container located on the driver's side at the rear of the engine compartment, and it is mounted on top of the master cylinder. Open the reservoir cap and use the baster to remove as much brake fluid as possible from the reservoir. Refill the reservoir with new fluid that corresponds to the manufacturer's specification, and replace the reservoir cap. The correct type of brake fluid for your vehicle is listed in the vehicle's owner's manual, and is usually printed on the brake fluid reservoir cap.

4

Slowly open the bleeder nut until you see brake fluid dripping slowly through the tubing. Have an assistant start the car and gently press on the brake pedal. You will see fluid squirt out of the bleeder when the brake pedal is pushed. Carefully examine the fluid coming out of the bleeder for signs of contamination. Contaminated fluid will be discolored and cloudy, while new fluid is transparent and clean in appearance. When the brake pedal is approaching the floor, close the bleeder nut to prevent air from flowing back into the brake. Continue this process, refilling the brake fluid reservoir as required, until you see clean, new fluid coming out of the bleeder nut. Tighten the bleeder nut and remove the tubing. Move to the rear driver's side brake and repeat the procedure, followed by the front passenger side brake, and finally the front driver's side brake.

5

Top up the brake fluid reservoir to the maximum level mark, and replace the cap. Test the brake operation before driving the vehicle normally.