Master Cylinder Priming - In-Vehicle or Bench

Special Tools:

WARNING: Brake fluid contains polyglycol ethers and polyglycols. Avoid contact with eyes. Wash hands thoroughly after handling. If brake fluid contacts eyes, flush eyes with running water for 15 minutes. Get medical attention if irritation persists. If taken internally, drink water and induce vomiting. Get medical attention immediately.

CAUTION: Do not allow the brake master cylinder reservoir to run dry during the bleeding operation. Keep the brake master cylinder reservoir filled with the specified brake fluid. Never reuse the brake fluid that has been drained from the hydraulic system.

CAUTION: Brake fluid is harmful to painted and plastic surfaces. If brake fluid is spilled onto a painted or plastic surface, immediately wash it with water.

NOTE: When any part of the hydraulic system has been disconnected for repair or installation, air can get into the system and cause spongy brake pedal action. This requires bleeding of the hydraulic system after it has been correctly connected. The hydraulic system can be bled manually or with pressure bleeding equipment.

NOTE: When the brake master cylinder has been installed new or the system has been emptied or partially emptied, it must be primed to prevent air from entering the system.





1. For in-vehicle priming, disconnect the brake lines from the brake master cylinder.





2. For bench priming, mount the brake master cylinder in a vise.





3. Install short brake tubes with the ends bent into the brake master cylinder reservoir.
^ Fill the brake master cylinder reservoir with High Performance DOT 3 Brake Fluid C6AZ-19542-AB or DOT 3 equivalent meeting Ford specification ESA-M6C25-A.





4. For a new brake master cylinder, remove the cruise switch.





5. Fill the cruise switch with the specified brake fluid.





6. Install the cruise switch.
7. Slowly depress the primary piston or, for in-vehicle priming, have an assistant slowly pump the brake pedal until clear brake fluid flows from both brake tubes with no air bubbles.
8. If necessary, install the brake master cylinder into the vehicle.





9. Remove the short brake tubes and install the master cylinder outlet tubes.





10. Loosen a brake outlet tube at the 4WABS hydraulic control unit (HCU).

11. NOTE: Refill the brake master cylinder reservoir as necessary.

Have an assistant depress and hold the brake pedal.





12. Tighten the outlet tube fitting at the HCU.
13. Repeat the above three steps until no air bubbles are seen in the expelled brake fluid.





14. Repeat the above four steps for the remaining master cylinder outlet tube.





15. Connect one end of a flexible tube to the master cylinder bleeder screw. Submerge the other end in a container partially filled with the specified brake fluid.
16. Have an assistant pump and then hold firm pressure on the brake pedal.

17. NOTE: Refill the brake master cylinder reservoir as necessary.

Loosen the master cylinder bleeder screw until brake fluid flows out of the drain tube.





18. Tighten the master cylinder bleeder screw.
19. Repeat the above three steps until there are no air bubbles in the expelled brake fluid.
20. Bleed the brake system.