Brake Proportioning Valve

This procedure replaces the brake proportioning valve, which controls hydraulic pressure distribution between front and rear brakes to prevent rear wheel lockup during braking.

Warnings

Tools required

Parts

• Brake proportioning valve assembly × 1 — Use OEM Ford specification
• Brake line crush washers/seals (if equipped) × 4 — Verify with specific valve type

Fluids

• Motorcraft DOT 4 LV Brake Fluid — 1 qt

Preparation

1. Park vehicle on level surface and engage parking brake firmly
2. Chock front wheels securely to prevent any vehicle movement
3. Verify brake fluid reservoir is accessible and note current fluid level
4. Ensure you have a complete brake bleeding kit and assistant if not using a pressure bleeder
5. Locate the proportioning valve on the frame rail near the rear axle (typically passenger side)
6. Take photos of brake line routing and connections before disassembly for reference
7. If brake lines show corrosion, apply penetrating oil to fittings 30 minutes before starting work

Procedure

1. 1

   Raise and support vehicle
   Lift the rear of the vehicle using a floor jack at the rear axle differential. Place jack stands under the frame rails behind the rear wheels at manufacturer-specified lift points. Lower vehicle onto jack stands and verify stability. Remove rear wheels if necessary for access to proportioning valve mounting location.
   ⚠️Never work under a vehicle supported only by a jack. Always use rated jack stands on solid frame contact points.
2. 2

   Prepare brake fluid reservoir
   Open the hood and locate the brake fluid reservoir on the master cylinder. Use a clean turkey baster or fluid transfer pump to remove brake fluid until reservoir is at minimum fill line. This minimizes fluid loss during line disconnection. Dispose of old fluid properly. Leave reservoir cap loose but in place to prevent vacuum formation.
3. 3

   Identify and label brake lines
   Locate the proportioning valve on the frame rail. Identify all brake lines connected to the valve: typically one inlet line from the master cylinder and two outlet lines to rear brakes. Use masking tape to label each line with its position (inlet, left rear, right rear) to ensure correct reinstallation. Take additional photos if needed.
4. 4

   Disconnect inlet brake line
   Position drain pan under proportioning valve. Using the appropriate size flare nut wrench, carefully loosen the inlet brake line fitting at the proportioning valve (this is the line coming from the front of the vehicle/master cylinder). Use a backup wrench on the valve body to prevent twisting. Once loose, carefully unthread the fitting by hand and immediately plug or cap the open line to minimize fluid loss and contamination.
   ⚠Use only flare nut wrenches on brake line fittings. Standard open-end wrenches will round off the soft brass fittings.
5. 5

   Disconnect outlet brake lines
   Using the flare nut wrench, disconnect both rear outlet brake lines from the proportioning valve in the same manner as the inlet line. Hold the valve body with a backup wrench to prevent rotation. Cap or plug all open lines immediately. Allow brake fluid to drain into the pan. Note the condition of any copper crush washers or seals at the fittings for replacement.
6. 6

   Remove proportioning valve mounting bolts
   Locate the mounting bolts securing the proportioning valve bracket to the frame rail. Remove these bolts completely using the appropriate socket or wrench. Support the valve assembly as you remove the last bolt to prevent it from falling. Remove the valve assembly from the vehicle.
   ⚠Brake fluid will continue to drip from the valve. Keep drain pan positioned throughout removal.
   Torque spec

   Proportioning Valve Bolts15 Nm (11 lb-ft)
7. 7

   Prepare new proportioning valve
   Remove the new proportioning valve from packaging and verify it matches the original valve exactly. Check that all port threads are clean and undamaged. If the valve includes new mounting hardware or seals, verify all components are present. Inspect the mounting bracket for any damage or corrosion and clean the frame mounting surface with a wire brush if needed.
8. 8

   Install new proportioning valve
   Position the new proportioning valve and bracket assembly onto the frame rail, aligning the mounting holes. Start all mounting bolts by hand to ensure proper thread engagement. Tighten mounting bolts to specification using a torque wrench in a cross pattern if multiple bolts are used. Ensure the valve ports are oriented correctly to align with the brake lines.
   ⚠Do not overtighten mounting bolts as this can crack the valve body. Always use a torque wrench.
   Torque spec

   Proportioning Valve Bolts15 Nm (11 lb-ft)
9. 9

   Connect inlet brake line
   Remove the plug from the inlet brake line and the inlet port on the new proportioning valve. If the valve uses copper crush washers or seals, install new ones now. Thread the inlet line fitting into the valve port by hand until snug to ensure proper thread engagement. Use a flare nut wrench to tighten the fitting to specification while holding the valve body with a backup wrench.
   ⚠Cross-threading brake line fittings will ruin the valve. Always start fittings by hand and ensure smooth threading before using wrenches.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
10. 10

    Connect outlet brake lines
    Remove plugs from both outlet brake lines and the corresponding valve ports. Install new seals if applicable. Connect each rear brake line to its correct port on the proportioning valve, referring to your labels and photos. Thread each fitting by hand first, then tighten to specification using flare nut wrenches and a backup wrench on the valve body.
    ⚠️Connecting brake lines to incorrect ports will cause improper brake pressure distribution and potential brake failure. Verify connections match original configuration.
    Torque spec

    Brake Line Fittings15 Nm (11 lb-ft)
11. 11

    Reinstall rear wheels
    If rear wheels were removed, reinstall them now. Install lug nuts by hand, then tighten in a star pattern to specification using a torque wrench. This allows the vehicle to be lowered for the bleeding process.
    Torque spec

    Wheel Lug Nuts169 Nm (125 lb-ft)
12. 12

    Bleed brake system completely
    Fill brake fluid reservoir to MAX line with fresh Motorcraft DOT 4 LV brake fluid. Bleed the entire brake system starting with the wheel farthest from the master cylinder (typically right rear), then left rear, right front, and left front. At each wheel, attach a clear hose to the bleeder screw with the other end submerged in a container of clean brake fluid. Have an assistant pump the brake pedal 3-5 times and hold, then open the bleeder screw to release fluid and air. Close bleeder before pedal reaches floor. Repeat until no air bubbles appear in the discharged fluid. Tighten each bleeder screw to specification after bleeding that wheel. Maintain reservoir fluid level throughout bleeding process.
    ⚠️Never let the brake fluid reservoir run empty during bleeding or you will introduce air into the master cylinder and ABS unit, requiring additional bleeding procedures.
    ⚠The brake pedal will feel soft until system is completely bled. Do not attempt to drive the vehicle until pedal is firm and all air is removed.
    Torque spec

    Bleeder Screw16 Nm (12 lb-ft)
13. 13

    Inspect for leaks
    With the brake system bled and reservoir filled to MAX line, have an assistant apply firm, steady pressure to the brake pedal for 30 seconds while you inspect all connections at the proportioning valve. Look for any signs of fluid seepage or drips. Wipe all fittings dry with a clean towel and recheck. If any leaks are found, release pedal pressure, correct the issue, and re-bleed that portion of the system.
    ⚠️Any brake fluid leak is a critical safety issue. Do not proceed until all connections are completely dry under pressure.

Reassembly

1. Verify all brake line fittings are torqued correctly and show no signs of leakage
2. Ensure brake fluid reservoir is filled to MAX line with fresh DOT 4 LV fluid
3. Lower vehicle from jack stands and remove wheel chocks
4. Clean any spilled brake fluid from frame and surrounding components with water
5. Dispose of old brake fluid according to local environmental regulations

Verification

• With engine off, pump brake pedal several times. Pedal should build firm resistance and not sink to the floor
• Start engine and verify brake pedal does not sink when steady pressure is applied for 30 seconds
• Perform a low-speed brake test in a safe area (empty parking lot). Brakes should engage smoothly with no pulling to one side
• Check under vehicle one final time for any brake fluid leaks at all proportioning valve connections
• Test drive at progressively higher speeds in a safe area, verifying proper brake function and pedal feel
• Perform several moderate to firm stops from 30-40 mph to verify rear brakes are not locking prematurely
• After test drive, recheck all connections for leaks and verify brake fluid reservoir level
• If brake pedal feels soft, ABS light illuminates, or braking performance is abnormal, do not drive vehicle and seek professional assistance immediately

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