Bleeding brake fluid will guarantee that no air bubbles are trapped in a car’s brake lines. Fluids transfer force from the master cylinder to the corners of the car, because fluids maintains their state, and do not compress, when brakes are pushed. When too much air has accumulated in the system, braking will compress the air, instead of creating pressure at the brake corners. Air in the lines may cause the pedal to feel spongy when pressed down, and large amounts of air may cause brakes to fail. Fluids only need to be changed once every two to three years in a standard-use car, as long as the hoses maintain integrity.
Choosing the right brake fluid is crucial. Most general-use cars should use a DOT-3, which has a dry boiling point of 205 degrees Celsius and a wet boiling point of 140 degrees Celsius. DOT-4 has a slightly higher boiling point, but is also much more viscous, making it a poor choice for some vehicles. DOT-5 fluids, which are silicone-based, are best for cars which are not driven often, such as older cars which are being restored. Silicone-based fluids should never be used in a car with an anti-lock braking system.
The process is easiest when all four car wheels are off of the ground. However, since most home mechanics don’t have that capability, the car can stay on the ground, as long as there’s room to use a wrench on bleeder valves. Loosening bleeder valves may be a challenge, so a drizzle of penetrating oil the day before brakes are bled will help to budge the bolts. A box wrench which fits the brake bolts is the best tool for the job. Tapping lightly with a hammer will help to loosen bolts, and break through corrosion.
In the beginning, bleeder valves should be loosened, but not open. Then, utilizing a disposable turkey baster from the kitchen, car owners should suck out as much of the old, inky liquid as possible, from the top of the master cylinder reservoir. Any visible contaminants within the reservoir should be cleaned with a lint-free rag. Also, car owners must be careful with brake fluid, which will immediately ruin any painted surface.
Car owners should push one end of a piece of cheap aquarium tubing, over one of the bleeder bolts. The other end should be placed into a clear plastic bottle, into which about an inch of clean brake fluid has been poured. Under the pedal, a one-by-four piece of wood should be placed, to keep the pedal from being depressed too far, when line pressure is released. Then, fresh brake fluid should be poured into the master cylinder reservoir, before replacing the cap.
The next steps in the process are easiest with a helper, to push the pedal. The car owner should signal the helper to push the pedal down, and, when the pedal is pushed down, should turn the bleeder bolt about a quarter turn. Old liquid will trickle into the clear container, through the aquarium tubing. When the trickle stops, the car owner should signal the helper to release the pedal, and should close the bleeder valve. This process should be repeated, until clean liquid begins to come through the tubing, into the container.
After five pushes of the pedal, the fluid in the master cylinder reservoir should be topped off. Allowing the reservoir to be less than half full invites more air into the system, which defeats the purpose of bleeding the brakes. When clean fluid is coming from the brake, then the bleeder bolt should be tightened. Then, the bleeding process should be started on another wheel, until all four wheels have been bled of contaminated fluid.
To dispose of old or unused liquid, pour it into a container of kitty litter. The liquid will evaporate within a few days, and the contaminated litter may be thrown in the garbage, in a closed plastic grocery bag. To decrease the likelihood of waste, car owners should always purchase eight-ounce containers of fluids, instead of purchasing larger containers. Always, old fluids, even when drying in kitty litter, must be kept away from animals and children. Also, fluids are extremely flammable, and must be kept away from any ignition source.
Bleeding an anti-lock braking system may be more complicated, so car owners should consult their owner’s manual before making an attempt. By bleeding the lines every two years, or every 24,000 miles, car owners will ensure that components, including calipers and the master cylinder, last for a long time. The right fluid, the right tools, and the right helper will make bleeding brake fluid an easier, if not less dirty, job.