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Brake Plumbing

What You Need to Haul Your Ford Down
By Dick Harrington

Upgrading your brake system is a common discussion among classic Ford owners, especially when it comes to disc brake upgrades and dual master cylinder conversions. However, one often-misunderstood element of these upgrades is properly distributing brake fluid to each wheel. Incorrect fluid distribution can be extremely dangerous, making it crucial to ensure your system is installed correctly.

Key Considerations for Brake Upgrades

  1. Master Cylinder and Distribution Block:
    Properly match these components to your braking system.
  2. Reputable Components:
    Use a complete system from a trusted supplier or ensure all donor components are included when sourcing from a later-model Ford.
  3. System Design:
    Study the installation process to avoid costly mistakes.

Disc Brake Complexity

When replacing front drum brakes with disc brakes, the system becomes more complex:

  • Disc Brakes:
    Operate without return springs, which means they react more quickly.
  • Rear Drum Brakes:
    Require a constant low-level pressure to prevent wheel cylinder seals from leaking.

Combination Valve

A combination valve balances the braking system by managing fluid distribution, proportioning, and metering. Let’s break down its functions in 1970–1980 Ford vehicles with front disc and rear drum brakes:

  1. Fluid Distribution:

    • Ford master cylinders have two outlets to distribute fluid to four wheels.

  2. Proportioning:

    • Disc brakes require more fluid than drum brakes.
    • The valve reduces fluid to rear drums to prevent rear wheel lockup during hard braking, particularly on slippery roads.

  3. Pressure Differential Sensing:

    • Mandated in 1967 for safety, dual master cylinders require a warning light to indicate brake failure.
    • If there’s a fluid leak, a sensor in the combination valve activates the warning light.

  4. Metering Valve:

    • Keeps front disc brakes from activating before rear drum brakes during light braking.
    • Ensures better braking balance and minimizes premature front brake wear.

Ford combination valves with a metering function often include a bleeder valve for easy identification.

Residual Pressure

Drum brakes require 6–25 psi of residual pressure to maintain seal integrity in the wheel cylinders.

  • Ford Design:
    • Residual check valves are built into the master cylinder for drum brakes.
    • When disc brakes were added, the residual check valve was removed from the disc brake circuit.

Using a drum brake master cylinder on disc brakes can cause front brake drag, so selecting the correct master cylinder is critical.

Master Cylinder Bore and Reservoirs

  • Bore Size:

    • Larger bores require less pedal stroke but more effort.
    • Smaller bores require more stroke but less effort.
    • Power brake systems typically use a larger bore than manual systems.

  • Reservoirs:

    • Dual master cylinders have two reservoirs.
    • For disc and drum setups, the larger reservoir (usually in the rear) supplies the disc brakes due to their higher fluid demand.

Important Considerations for Brake Upgrades

  1. Purchase a Complete System:
    • Whether buying new or sourcing from a donor vehicle, ensure all components (calipers, rotors, master cylinder, etc.) are included.
  2. Use the Correct Master Cylinder:
    • Ensure compatibility with your specific braking system.
  3. Rod Length:
    • If upgrading to a dual reservoir master cylinder, the push rod length must match the original.
    • A rod that’s too short may result in insufficient braking force, while one that’s too long may prevent brakes from fully releasing.

Cautions and Tips

  • Be cautious when sourcing parts and advice online. Verify the supplier’s credibility and ensure parts are designed for street use if applicable.
  • Adjustable Valves:
    • While adjustable valves are available, randomly adjusting them to balance front and rear braking can be dangerous.

Conclusion

Upgrading your braking system requires careful planning and attention to detail. Always prioritize safety by using high-quality, properly matched components. With the correct setup, you can enjoy the performance and peace of mind of a well-balanced braking system.