Brake Bleeding: Service and Repair

Pressure bleeding is recommended for all hydraulic brake systems.
The bleeding operation itself is fairly well standardized. First step in all cases is cleaning the dirt from the filler cap before removing it from the master cylinder. This should be done thoroughly.
Pressure bleeding is fastest because the master cylinder doesn't have to be refilled several times, and the job can be done by one man. To prevent air from the pressure tank getting into the lines, do not shake the tank while air is being added to the tank or after it has been pressurized. Set the tank in the required location, bring the air hose to the tank, and do not move it during the bleeding operation. The tank should be kept at least one-third full.
On vehicles equipped with disc brakes and master cylinders without proportioners or pressure control valves located in the master cylinder outlet port, the brake metering valve or combination valve must be held in position using a suitable tool.
If air does get into the fluid, releasing the pressure will cause the bubbles to increase in size, rise to the top of the fluid, and escape. Pressure should not be greater than about 35 psi.
On vehicles equipped with plastic reservoirs, do not exceed 25 psi bleeding pressure.
When bleeding without pressure, open the bleed valve three-quarters of a turn, depress the pedal a full stroke, then allow the pedal to return slowly to its released position. It is suggest that after the pedal has been depressed to the end of its stroke, the bleeder valve should be closed before the start of the return stroke. On cars with power brakes, first reduce the vacuum in the power unit to zero by pumping the brake pedal several times with the engine off before starting to bleed the system.
Pressure bleeding, of course, eliminates the need for pedal pumping.
Discard drained or bled brake fluid. Care should be taken not to spill brake fluid, since this can damage the finish of the car.
Flushing is essential if there is water, mineral oil or other contaminants in the lines, and whenever new parts are installed in the hydraulic system. Fluid contamination is usually indicated by swollen and deteriorated cups and other rubber parts.
Wheel cylinders on disc brakes are equipped with bleeder valves, and are bled in the same manner as wheel cylinders for drum brakes.
Bleeding is necessary on all four wheels if air has entered the system because of low fluid level, or the line or lines have been disconnected. If a line is disconnected at any one wheel cylinder, that cylinder only need be bled. Of course, on brake reline jobs, bleeding is advisable to remove any air or contaminants.
Master cylinders equipped with bleeder valves should be bled first before the wheel cylinders are bled. In all cases where a master cylinder has been overhauled, it must be bled. Where there is no bleeder valve, this can be done by leaving the lines loose, actuating the brake pedal to expel the air and then tightening the lines.
After overhauling a dual master cylinder used in conjunction with disc brakes, it is advisable to bleed the cylinder before installing it on the car. The reason for this recommendation is that air may be trapped between the master cylinder pistons because there is only one residual pressure valve (check valve) used in these units.

TESTING DUAL MASTER CYLINDERS
Be sure that the master cylinder compensates in both parts. This can be done by applying the brake pedal lightly (engine running with power brakes) and observing for brake fluid squirting up in the reservoirs. This may only occur in the front chamber. To determine if the rear compensating port is open, pump up the brakes rapidly and hold the pedal down. Have an observer watch the fluid in the rear reservoir while the pedal is raised. A disturbance in the fluid indicates that the compensating port is open.

WHEEL BLEEDING SEQUENCE
Rear Wheel Drive RR-LR-RF-LF
Front Wheel Drive RR-LF-LR-RF

DUAL MASTER CYLINDER BLEEDING NOTES
The following notes apply to master cylinders without proportioners or pressure control valves located in the master cylinder outlet ports.
1982-87 cars use a self-centering valve. After any bleeding operation, turn ignition switch to ACC or ON position and depress brake pedal. Valve will center itself.