Brake Proportioning Valve

Remove and replace the brake proportioning valve on a 2005 Dodge Viper, ensuring proper brake bias distribution between front and rear axles. Complete system bleeding is required after replacement.

Warnings

Tools required

Parts

• Brake proportioning valve assembly × 1 — Use OEM specification - Mopar replacement recommended
• Brake line crush washers or seals (if equipped) × 1 — Verify fitment for proportioning valve connections
• DOT 4 brake fluid × 1 — Minimum 1 quart for system refill and bleeding

Fluids

• brake — 1 qt

Preparation

1. Park vehicle on level ground and engage parking brake firmly.
2. Chock rear wheels securely with wheel chocks on both sides.
3. Open hood and prop securely. Locate brake master cylinder reservoir.
4. Check current brake fluid level and condition. Note color and clarity for comparison after service.
5. Gather all tools, parts, and at least 1 quart of fresh DOT 4 brake fluid from sealed container.
6. Put on safety glasses and nitrile gloves. Lay out shop towels around brake master cylinder area.
7. Prepare brake line plugs or caps to seal open lines immediately after disconnection.
8. Locate proportioning valve - trace brake lines from master cylinder toward rear of vehicle to identify valve body and mounting location.
9. If working alone, ensure you have a method to bleed brakes (pressure bleeder recommended) or arrange for an assistant.

Procedure

1. 1

   Remove master cylinder reservoir cap and extract fluid
   Remove the brake master cylinder reservoir cap. Using a clean turkey baster or fluid extraction syringe, remove as much brake fluid as possible from the reservoir to minimize spillage during line disconnection. Dispose of old fluid properly - never reuse. Leave cap off for now to monitor fluid level.
2. 2

   Identify and mark brake line connections
   Locate the proportioning valve assembly. It will have multiple brake line connections - typically one inlet from the master cylinder and two or more outlets to the rear brake circuits. Use masking tape or a marker to label each brake line connection (inlet, left rear, right rear, etc.) to ensure correct reconnection. Take a photo for reference if possible.
3. 3

   Disconnect brake lines from proportioning valve
   Place a drain pan under the proportioning valve. Using the correct size flare nut wrench (typically 3/8" or 7/16" for these lines), carefully loosen each brake line fitting at the proportioning valve. Work slowly to avoid rounding the soft brass fittings. Loosen all fittings first, then unthread them completely by hand. Immediately cap or plug each open line and valve port to prevent fluid loss and contamination. Expect significant fluid drainage - keep drain pan positioned and have shop towels ready.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
4. 4

   Remove proportioning valve mounting hardware
   Locate the proportioning valve mounting bolts or bracket. The valve may be mounted directly to the frame rail or to a dedicated bracket. Remove the mounting bolts completely. On this platform, expect 2 mounting bolts securing the valve assembly. Use a socket or combination wrench as access permits. Keep mounting hardware organized for reinstallation.
   Torque spec

   Proportioning Valve Bolts15 Nm (11 lb-ft)
5. 5

   Remove proportioning valve from vehicle
   Carefully maneuver the proportioning valve assembly away from its mounting location. Some brake fluid will continue to drip from the ports - keep drain pan positioned. Inspect the mounting area for corrosion, damage, or debris. Clean mounting surface with a wire brush if necessary. Verify the new proportioning valve matches the original in port configuration and mounting holes.
6. 6

   Prepare and install new proportioning valve
   Remove all protective caps from the new proportioning valve ports. Inspect all ports for debris or damage. If the valve uses crush washers or seals at the line connections, install new ones now (do not reuse old seals). Position the new proportioning valve into the mounting location, aligning mounting holes with frame or bracket. Start mounting bolts by hand to ensure proper thread engagement.
   Torque spec

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

   Torque proportioning valve mounting bolts
   Tighten the proportioning valve mounting bolts to the value specified in the factory service manual (verify OEM spec) in an alternating pattern if multiple bolts are present. Ensure the valve body is seated flush against its mounting surface and is not cocked or misaligned. Verify there is adequate clearance around all ports for brake line installation.
   Torque spec

   Proportioning Valve Bolts15 Nm (11 lb-ft)
8. 8

   Reconnect brake lines to proportioning valve
   Remove caps/plugs from brake lines and valve ports. Thread each brake line fitting into the correct port on the proportioning valve by hand first - refer to your labels/photo from step 2. Ensure fittings thread smoothly without cross-threading. Hand-tighten all fittings until snug, then use the flare nut wrench to tighten to the brake line fitting torque specified in the factory service manual (verify OEM spec). Work in the sequence recommended by the service manual if available, typically starting with the inlet line from the master cylinder, then outlet lines. Do not overtighten - brass fittings strip easily.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
9. 9

   Refill brake master cylinder reservoir
   Fill the brake 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 let it drop below the MIN line or air will enter the system.
10. 10

    Bleed brake system starting at proportioning valve
    Locate the bleeder screw on the proportioning valve body (if equipped - not all valves have one). If present, attach clear tubing to the bleeder and submerge the other end in a container of clean brake fluid. Have an assistant pump the brake pedal 3-4 times and hold pressure, then open the bleeder screw 1/4 turn. Watch for air bubbles in the tubing. Close bleeder before pedal reaches floor. Repeat until fluid flows clear without bubbles. Tighten bleeder screw to the torque specified in the factory service manual (verify OEM spec). Refill reservoir frequently.
    Torque spec

    Bleeder Screw14 Nm (10 lb-ft)
11. 11

    Bleed all four wheel brake calipers
    Bleed the brake system in the sequence specified in the factory service manual for this vehicle. If unavailable, the general guideline is furthest from the master cylinder to closest, but verify the correct order for the Viper before proceeding. For each caliper, attach clear tubing to the bleeder screw and submerge the other end in clean brake fluid. Have an assistant pump the brake pedal 3-4 times and hold pressure. Open bleeder screw 1/4 turn, allow fluid to flow until no air bubbles appear, then close bleeder before pedal reaches floor. Repeat 2-3 times per wheel. Tighten all bleeder screws to the torque specified in the factory service manual (verify OEM spec). Constantly monitor and refill master cylinder reservoir.
    Torque spec

    Bleeder Screw14 Nm (10 lb-ft)
12. 12

    Verify brake pedal feel and check for leaks
    With engine off, pump brake pedal firmly 10-15 times. Pedal should feel firm and consistent with minimal travel. If pedal feels spongy or sinks slowly, repeat bleeding procedure. Start engine (pedal will drop slightly - this is normal with power brakes). Recheck pedal feel with engine running. Inspect all brake line connections at the proportioning valve for any signs of leakage. Wipe connections dry and observe for fresh fluid weeping. Check master cylinder reservoir level and top off to MAX line.
13. 13

    Perform brake system function test
    In a safe area with no traffic, perform multiple test stops from low speed (15-20 mph). Verify brakes apply smoothly without pulling to one side. Gradually increase test speed to verify proper brake function and proportioning. Monitor brake warning lights on instrument cluster - none should illuminate. If any abnormality is detected (pulling, soft pedal, warning lights), do not drive the vehicle. Recheck all connections and repeat bleeding procedure.

Reassembly

1. Reinstall master cylinder reservoir cap securely.
2. Clean any spilled brake fluid from painted surfaces, components, and frame immediately with water.
3. Dispose of old brake fluid according to local regulations - never pour down drains or onto ground.
4. Remove wheel chocks and lower vehicle completely if raised.
5. Final brake fluid level should be at MAX line on reservoir with system at rest.

Verification

• Start engine and verify brake pedal is firm with approximately 1-2 inches of free play before resistance is felt.
• No brake warning lights should be illuminated on instrument cluster.
• Visually inspect all brake line connections at proportioning valve - no leaks or fluid seepage should be present.
• Test drive vehicle in safe area, performing multiple stops from various speeds. Brakes should apply smoothly and evenly without pulling.
• Recheck master cylinder fluid level after test drive - level should remain at MAX line.
• After 24 hours and 50-100 miles of driving, recheck all connections for leaks and verify pedal feel remains firm. This is critical for safety.
• If vehicle exhibits any brake pulling, uneven pad wear, or premature rear lockup, proportioning valve may require adjustment or replacement with correct specification for vehicle brake package.

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