It may be necessary to bleed the hydraulic system of all four brake mechanisms if air has entered the system due to low brake fluid level or if the brake lines have been disconnected from the master cylinder.
If the brake line was disconnected on only one wheel, then only that wheel cylinder needs to be bled (or support).
If the brake line has been disconnected between the master cylinder and any of the wheel brakes, the air must be removed from the part of the brake system to which the brake fluid was supplied through the disconnected line.
If the master cylinder has been removed from the vehicle, bleed it before installing it.
If the master cylinder is installed on the vehicle but is known to contain air, it must be bled before bleeding the wheel cylinder (or support). To bleed air from the master brake cylinder installed on a vehicle, proceed as follows.
Press the brake pedal several times with the engine stopped to relieve the vacuum in the brake booster.
Remove the cap from the reservoir and fill it with brake fluid, then monitor the fluid level in the reservoir while bleeding air, adding fluid as needed. Replace the cover.
Disconnect the front brake line from the master cylinder.
Allow brake fluid to fill the master cylinder until it comes out of the front line connection.
Connect the front brake line to the master cylinder.
Ask an assistant to press the brake pedal very slowly and hold it in this position.
Loosen the front brake line retaining nut on the master cylinder, then tighten the connection and slowly release the brake pedal.
Wait 15 seconds (this is very important).
Repeat the operations, including a 15-second pause, until all air has escaped from the master cylinder.
Once the front connection has been completely cleared of air, remove air from the rear connection in a similar manner.
Before bleeding individual wheel cylinders or calipers, perform the following steps.
Press the brake pedal several times with the engine stopped to relieve the vacuum in the brake booster.
Remove the cap from the brake master cylinder reservoir and fill it with brake fluid, then check the fluid level in the reservoir while bleeding, adding more fluid as needed. Replace the cover.
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Next, do the work with an assistant. You will need a container of fresh brake fluid, an empty clear plastic container, a set of 500mm long plastic, rubber or vinyl tubes to connect to the bleed nipple, and a wrench to loosen and tighten the bleed nipple. It is better to lift the car and secure it on stands.
Starting at the right rear wheel, loosen the bleed screw slightly, then tighten it until it is snug but can be released quickly and easily.
Place one end of the tube on the air bleed nipple and lower the other end into a container with brake fluid.
The assistant should press the brake pedal several times to create pressure in the system, then hold the pedal down.
With the pedal depressed, release the bleed screw until brake fluid begins to flow out of the screw. Observe air bubbles escaping through the end of the tube immersed in the container. When the fluid flow slows, close the bleed valve and have an assistant release the brake pedal.
Repeat these steps until no air bubbles are seen coming out of the tube, then tighten the bleed screw and move on to the left rear wheel, right front wheel, and left front wheel. Be sure to check the fluid level in the reservoir. Never use old brake fluid as it contains excess moisture which will deteriorate the condition of the brake system components.
After removing the air, refill the reservoir with brake fluid.
If you have any difficulty bleeding the hydraulic system or do not have an assistant, you can purchase a pressure bleeding kit. Once connected according to the instructions, each of the air bleed nipples can be opened in turn to remove the fluid under pressure until it is free of air bubbles, and there is no need to fill the tank during bleeding.