If you've recently done brake work on your Ford Truck and you get a constant or even random soft brake pedal you may still have air trapped in the system even after bleeding. Air can get trapped in the system and a special procedure is required.
If equipped with the 4 wheel anti-lock brake system and the Hydraulic Control Unit (HCU) has been replaced or is suspected of containing trapped air; bleed the brake system using the procedure below. Conventional brake system bleeding cannot remove the air trapped in the lower portion of the HCU. If a spongy brake pedal is present and air in the hydraulic control unit is suspected, use the following procedure:
1. Bleed the brake system as outlined in the conventional bleeding procedure.
2. Connect a tester or equivalent scan tool, to the serial data link connector below the instrument panel as though retrieving codes.
3. Make sure the ignition switch is in the RUN position.
4. Follow the instructions on the screen. Verify correct vehicle and model year go to the "Diagnostic Data Link' menu item, choose ABS Module, choose "Function Tests", and choose "Service Bleed."
5. Bleed the right-front wheel as follows:
- Open the caliper bleed screw and pump the brake pedal for 3 seconds. Repeat the procedure again.
- When the fluid runs clear, begin the program and continue to pump the brake pedal.
- Continue bleeding for approximately 1 to 2 minutes after the program ends and then tighten the bleed screw.
6. Repeat the bleeding procedure to the left-front, left-rear and finally the right-rear wheel.
7. Remove the pressure bleeding device and adjust the brake fluid level.
8. Road test the vehicle and check for proper brake system operation.