Brake Proportioning Valve

Replacement of the brake proportioning valve, which regulates hydraulic pressure distribution between front and rear brake circuits to prevent premature rear wheel lockup during braking.

Warnings

Tools required

Parts

• Brake proportioning valve assembly × 1 — Use OEM specification
• Brake line crush washers (if applicable) × 4 — Use OEM specification
• DOT 3 brake fluid × 1 — Meeting DOT 3 specification

Fluids

• brake — 1 qt

Preparation

1. Park vehicle on level, solid surface and apply parking brake firmly
2. Place wheel chocks behind rear wheels
3. Open brake fluid reservoir cap to relieve vacuum and facilitate fluid flow during removal
4. Place absorbent material or cardboard under work area to catch brake fluid spills
5. Gather all tools and new parts before beginning work
6. Ensure you have at least 1 quart of fresh DOT 3 brake fluid from a sealed container
7. Review complete procedure before starting work

Procedure

1. 1

   Locate proportioning valve
   The brake proportioning valve is mounted on the driver side frame rail near the master cylinder, just forward of the driver's door. It is a cylindrical brass or steel component with four brake line connections (two inlet lines from master cylinder, two outlet lines to rear brakes). Use a flashlight to positively identify the valve and inspect all brake line connections for corrosion or damage.
2. 2

   Reduce brake fluid level in reservoir
   Using a turkey baster or brake fluid syringe, remove approximately half the brake fluid from the master cylinder reservoir to prevent overflow when disconnecting lines. Transfer removed fluid to a waste container; do not reuse. This step minimizes fluid loss and mess during valve removal.
3. 3

   Mark and document brake line positions
   Before disconnecting any lines, use masking tape or a marker to label each of the four brake lines at the proportioning valve: mark the two inlet lines from the master cylinder and the two outlet lines going to the rear brakes. Take a photo for reference during reinstallation. Cross-connecting these lines will result in improper brake balance and potential brake failure.
4. 4

   Disconnect brake lines from proportioning valve
   Using the appropriate size flare nut wrench (typically 3/8" or 7/16" for this application), carefully loosen and remove all four brake line fittings from the proportioning valve. Work slowly to avoid rounding the soft brass fittings. Hold the valve body steady with one hand while turning the flare nut wrench. Allow brake fluid to drain into catch container. Cap or plug the open brake lines with rubber caps or clean shop towels to prevent contamination.
   ⚠Use only flare nut wrenches (also called line wrenches) on brake line fittings. Standard open-end wrenches will round off the soft brass fittings.
5. 5

   Remove proportioning valve mounting bolts
   Locate and remove the mounting bolts securing the proportioning valve to the frame bracket. The valve is typically held by 2 mounting bolts. Use the appropriate socket or wrench and support the valve as you remove the final bolt to prevent it from falling.
6. 6

   Remove old proportioning valve
   Carefully remove the proportioning valve assembly from its mounting bracket. Inspect the mounting bracket for corrosion, cracks, or damage. Clean the mounting surface with a wire brush and brake cleaner if necessary. Inspect all four brake line ends for damage to the flare seats; if any flare is damaged, the brake line must be replaced before proceeding.
7. 7

   Prepare new proportioning valve for installation
   Remove the new proportioning valve from its packaging and verify it matches the original valve in port configuration and mounting holes. Check that all four port threads are clean and undamaged. If the valve came with port plugs installed, do not remove them until ready to connect brake lines (this prevents internal contamination). Inspect any included crush washers or sealing washers.
8. 8

   Install new proportioning valve
   Position the new proportioning valve in the mounting bracket, aligning the mounting bolt holes. Install the mounting bolts hand-tight first to ensure proper alignment, then torque to specification. Ensure the valve is positioned so that all four brake line connections are accessible and aligned with their respective lines.
9. 9

   Reconnect brake lines to proportioning valve
   Remove any protective plugs from the proportioning valve ports. Thread each brake line fitting into the correct port by hand first, using your labeling from step 3 to ensure correct routing. Once all fittings are hand-tight and properly seated, use the flare nut wrench to tighten each fitting to specification. Work in a cross pattern (front inlet, rear outlet, opposite front inlet, opposite rear outlet) to ensure even seating. Verify each line is routed correctly before final tightening.
   ⚠️Double-check that inlet lines from the master cylinder connect to inlet ports and outlet lines to rear brakes connect to outlet ports. Incorrect routing will cause brake failure.
10. 10

    Inspect all connections for proper seating
    Visually inspect each of the four brake line connections at the proportioning valve to verify they are fully seated and properly aligned. Check that no cross-threading occurred and that each fitting drew down evenly. Wipe away any spilled brake fluid from the valve body and surrounding area with brake cleaner and shop towels.
11. 11

    Refill brake fluid reservoir
    Fill the master cylinder reservoir to the MAX line with fresh DOT 4 brake fluid from a sealed container. Keep the reservoir topped off throughout the bleeding process. Never allow the reservoir to run dry during bleeding or air will enter the master cylinder.
12. 12

    Bleed brake system completely
    Bleed the entire brake system starting with the wheel farthest from the master cylinder (typically right rear, then left rear, then right front, then left front). At each wheel, attach clear tubing to the bleeder screw and submerge the other end in a container of fresh brake fluid. Have a helper slowly pump the brake pedal 3-5 times and hold pressure. Open the bleeder screw, allow fluid and air to escape until flow stops, then close the bleeder before helper releases pedal. Repeat until no air bubbles appear in the tubing. Check and refill reservoir frequently. Torque each bleeder screw after bleeding that corner.
    ⚠️Never allow the brake fluid reservoir to run empty during bleeding. If reservoir runs dry, air will enter the master cylinder requiring master cylinder bench bleeding.
    ⚠The brake pedal must be held under pressure when opening bleeder screws and released only after bleeder is closed, or air will be drawn back into the system.
13. 13

    Test brake pedal feel
    With engine off, pump brake pedal several times. Pedal should feel firm and high. If pedal feels spongy or sinks slowly to the floor, air remains in the system and further bleeding is required. A properly bled brake system will have a firm, high pedal that maintains pressure when held.
14. 14

    Inspect for leaks
    With a helper applying firm, steady pressure to the brake pedal, carefully inspect all four brake line connections at the proportioning valve for any signs of fluid seepage or drips. Also inspect the valve body itself for leaks. Any leak, no matter how small, must be corrected before driving the vehicle. Dry all connections with a clean shop towel and recheck after 30 seconds of pedal pressure.

Reassembly

1. Reassembly is covered in the installation steps above, as this is primarily a replacement procedure
2. Ensure master cylinder reservoir is filled to MAX line with fresh DOT 3 brake fluid
3. Secure reservoir cap tightly
4. Clean any brake fluid residue from painted surfaces immediately to prevent paint damage

Verification

• With engine off, pump brake pedal firmly 5-10 times. Pedal must feel firm and high, not spongy or soft
• Perform static leak inspection: have helper hold firm brake pedal pressure for 2 minutes while you inspect all connections at proportioning valve with a flashlight. No leaks permitted
• Start engine and apply brakes firmly. Pedal should remain high and firm with engine running. Pedal should not sink or feel different than with engine off
• Perform careful low-speed test drive in a safe area (empty parking lot). Test brake application at 5-10 mph to verify normal brake function and proper pedal feel before driving on public roads
• During test drive, verify no pulling to one side during braking and that rear brakes are not locking prematurely
• After test drive, re-inspect all proportioning valve connections for leaks while helper applies brake pressure
• Road test at progressively higher speeds only after verifying proper function at low speeds
• Check brake fluid level in reservoir after test drive and top off if needed

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

Chasing one of these codes and not sure which part is guilty? Ask a master mechanic about YOUR car →

More procedures for this vehicle