It may be necessary to bleed the hydraulic system of all four brake mechanisms if air has entered the system due to a low level of brake fluid or the brake pipes have been disconnected from the brake master cylinder.
If the brake pipe was disconnected on only one wheel, then only that working brake cylinder needs to be bled (or caliper).
If the brake pipe was disconnected in the area between the master brake cylinder and any of the wheel brakes, it is necessary to remove air from the part of the brake system to which brake fluid was supplied through the disconnected pipe.
If the brake master cylinder was removed from the vehicle, bleed the air before installing it.
If the master cylinder is installed on the vehicle, but it is known that it contains air, it must be bled before starting to bleed the slave brake cylinder (or caliper). Remove air from the main brake cylinder installed on the car, perform as follows.
Press the brake pedal several times with the engine stopped to release the vacuum in the brake booster.
Remove the cap from the reservoir and fill it with brake fluid, then in the process of removing air, control the fluid level in the reservoir, adding fluid as needed. Replace the cover.
Disconnect the front brake line from the master cylinder.
Allow brake fluid to fill the brake master cylinder until it comes out of the front line connection.
Connect the front brake line to the master cylinder.
Have an assistant depress the brake pedal very slowly and hold it in that position.
Loosen the nut securing the front brake line to the master cylinder, then tighten the connection and slowly release the brake pedal.
Wait 15s (it is very important).
Repeat the operations, including a pause of 15 seconds, until all air has been expelled from the brake master cylinder.
Once the front connection is completely purged of air, bleed the rear connection in the same way.
Before bleeding individual working brake cylinders or calipers, perform the following operations.
Press the brake pedal several times with the engine stopped to remove the vacuum in the vacuum brake booster.
Remove the cap from the master cylinder reservoir and fill it with brake fluid, then check the fluid level in the reservoir while bleeding, adding it as necessary. Replace the cover.
Next, work with an assistant. You will need a container of fresh brake fluid, an empty clear plastic container, a set of 500mm plastic, rubber or vinyl tubing to connect to the bleeder screw, and a wrench to turn and tighten the bleeder screw. It is better to lift the car and fix it on stands.
Starting at the right rear wheel, loosen the bleeder screw slightly, then tighten to a tight but quick and easy to loosen torque.
Put one end of the tube on the bleed valve, lower the other end into a container with brake fluid.
The assistant should depress the brake pedal several times to pressurize the system, then hold the pedal depressed.
With the pedal depressed, release the bleed valve so that the brake fluid begins to flow out of the valve. Watch for air bubbles escaping through the end of the tube immersed in the container. When the fluid flow weakens, close the bleed valve and have an assistant release the brake pedal.
Repeat these steps until no air bubble-free brake fluid comes out of the tube, then tighten the bleeder screw and move to the left rear wheel, right front wheel and left front wheel. Be sure to check the fluid level in the tank. Never use old brake fluid as it contains excessive moisture which will degrade the brake system components.
After removing the air, refill the reservoir with brake fluid.
If there is any difficulty in bleeding the hydraulic system or there is no assistant, a pressure bleeding kit can be purchased. Once it is connected according to the instructions, each of the bleed valves can be opened one by one to remove pressurized fluid until it is free of air bubbles, without the need to refill the tank during pumping.