See Figures 1 and 2
This procedure requires the use of a special tool.
The hydraulic brake system must be bled whenever a fluid line has been disconnected or air gets into the system. A leak in the system may sometimes be indicated by the presence of a spongy brake pedal. Air trapped in the system is compressible and does not permit the pressure applied to the brake pedal to be transmitted solidly through to the brakes. The system must be absolutely free from air at all times. When bleeding brakes, begin at the wheel most distant from the master cylinder first, the next most distant second, and so on. During the bleeding operation, the master cylinder must be kept at least 3 / 4 full of brake fluid.
On 1973 and later models, a combination differential and proportioning valve is used in the system. It is attached to the inner side of the left frame rail. When bleeding the brakes, the metering section of the valve must be held open. Loosen the front mounting bolt of the valve and insert Tool J-23709, or J-26869, or its fabricated equivalent, under the bolt. Push in on the metering valve stem to open it and retighten the bolt to hold the tool in place. When bleeding is finished, loosen the bolt, remove the tool and retighten the bolt.
To bleed the master cylinder, loosen one of the line fittings at the master cylinder. Have an assistant slowly depress the brake pedal and hold it at the floor. When the pedal reaches the floor, tighten the fitting. Repeat this procedure until just fluid emerges at the fitting. Repeat the entire bleeding procedure for the other brake line. Make sure that you have absorbant rags under the fittings to catch the fluid. Wear goggles to avoid any fluid spray from hitting your eyes.
To bleed the brakes, first carefully clean all dirt from around the master cylinder filler plug. If a bleeder tank is used, follow the manufacturer's instructions. Remove the filler plug and fill the master cylinder to the lower edge of the filler neck. Clean off the bleeder connections at all of the wheel cylinders or disc brake calipers. Attach the bleeder hose and fixture to the right rear wheel cylinder bleeder screw and place the end of the tube in a glass jar, submerged in brake fluid. Open the bleeder valve 1 / 2 - 3 / 4 of a turn. Have an assistant depress the brake pedal and allow it to return slowly. Continue this pumping action to force any air out of the system. When bubbles cease to appear at the end of the bleeder hose, close the bleeder valve and remove the hose. Check the level of the brake fluid in the master cylinder and add fluid, if necessary.
After the bleeding operation at each caliper or wheel cylinder has been completed, fill the master cylinder reservoir and replace the filler plug.