Brake Booster

Replace the vacuum brake booster on a 2007 Ram 3500 with 5.9L Cummins diesel engine, restoring proper brake assist function.

Warnings

Tools required

Parts

• Brake booster × 1 — Use OEM specification for diesel application
• Brake master cylinder gasket/seal × 1 — Replace if damaged during removal
• Vacuum pump check valve (if applicable) × 1 — Inspect and replace if faulty

Fluids

• DOT 3 brake fluid — 1 qt

Preparation

1. Park vehicle on level ground and engage parking brake
2. Disconnect negative battery cable to prevent airbag deployment while working near steering column
3. Wait at least 2 minutes after battery disconnect before beginning work near airbag systems
4. Remove as much brake fluid as possible from master cylinder reservoir using turkey baster or fluid pump into drain pan
5. Chock rear wheels securely
6. Gather all tools and parts before beginning

Procedure

1. 1

   Access brake booster from interior
   Open driver's door and position yourself to work under the dashboard. Remove the lower dash panel if necessary for better access to the brake pedal assembly. Use a flashlight to locate the brake booster pushrod connection to the brake pedal arm.
2. 2

   Disconnect pushrod from brake pedal
   Locate the brake booster pushrod clevis pin that connects the pushrod to the brake pedal arm. Remove the retaining clip from the clevis pin using pliers or a flathead screwdriver. Slide the clevis pin out and disconnect the pushrod from the brake pedal. Note the orientation for reassembly.
3. 3

   Access engine compartment connections
   Move to the engine compartment. Locate the brake master cylinder mounted to the front of the brake booster on the firewall. Clean the area around the master cylinder and brake lines to prevent contamination.
4. 4

   Disconnect brake lines from master cylinder
   Using brake line wrenches to prevent rounding, carefully loosen and remove the brake lines from the master cylinder. Have shop rags ready to catch dripping fluid. Cap or plug the brake lines immediately to prevent fluid loss and contamination. Label lines if needed for reassembly reference.
   ⚠Use proper brake line wrenches to avoid rounding off brake line fittings. Rounded fittings may require line replacement.
5. 5

   Remove master cylinder from booster
   Remove the two nuts securing the master cylinder to the brake booster studs. Carefully pull the master cylinder straight off the booster studs and set aside in a clean area. Avoid tilting to minimize fluid spillage. Inspect the master cylinder seal and replace if damaged.
6. 6

   Disconnect vacuum line from booster
   Verify the brake assist type for this vehicle: some 5.9L Cummins Ram 3500 trucks use a vacuum booster fed by an engine-driven vacuum pump, while others use a hydro-boost system driven by power steering pressure. If equipped with a vacuum booster, locate the vacuum line connection on the brake booster (connected to the vacuum pump on diesel models). Release the clamp or fitting securing the vacuum hose to the booster. Pull the vacuum hose off the booster fitting. Check the check valve in the line for proper operation and replace if faulty. Inspect the vacuum pump and lines for leaks if booster failure is suspected.
   ℹ️The 5.9L Cummins uses an engine-driven vacuum pump to supply vacuum to the brake booster. Inspect the vacuum pump and lines for leaks if booster failure is suspected.
7. 7

   Remove booster mounting nuts
   From inside the vehicle under the dash, remove the four nuts securing the brake booster to the firewall. These nuts are located on the cabin side of the firewall behind the brake pedal support bracket. Use a socket and extension to reach all four mounting nuts. Support the booster as you remove the last nut.
8. 8

   Remove brake booster
   From the engine compartment, carefully pull the brake booster assembly away from the firewall, guiding the mounting studs out through the firewall. Maneuver the booster out of the engine bay, taking care not to damage surrounding components.
9. 9

   Prepare and install new booster
   Compare the old and new brake boosters to ensure correct replacement. Transfer the pushrod if necessary, ensuring it is adjusted to the same length as the original. Apply a thin coat of clean brake fluid to the master cylinder mounting surface seal. Position the new booster to the firewall from the engine compartment side, aligning the mounting studs with the firewall holes.
10. 10

    Secure booster to firewall
    From inside the vehicle, verify the booster pushrod is properly positioned to align with the brake pedal. From inside the vehicle under the dash, install the four mounting nuts onto the studs protruding through the firewall and tighten evenly in a cross pattern to ensure proper seating. Tighten securely but do not overtighten.
11. 11

    Reconnect pushrod to brake pedal
    From the vehicle interior, align the booster pushrod clevis with the brake pedal arm hole. Insert the clevis pin through the pedal arm and pushrod clevis. Install the retaining clip securely. Verify the connection is secure and the pedal moves freely.
12. 12

    Reconnect vacuum line
    Connect the vacuum hose to the brake booster fitting. Secure with the clamp or fitting, ensuring a tight seal. Check that the check valve is properly oriented (arrow should point toward the booster).
13. 13

    Install master cylinder
    Inspect and replace the master cylinder seal if damaged. Position the master cylinder onto the brake booster studs, ensuring the pushrod enters the master cylinder bore properly. Install the two mounting nuts and tighten securely in an alternating pattern.
14. 14

    Reconnect brake lines
    Remove plugs or caps from brake lines. Thread brake lines into the master cylinder ports by hand first to ensure proper thread engagement. Tighten brake line fittings using brake line wrenches to proper tightness. Do not overtighten.
15. 15

    Bleed brake system
    Fill the master cylinder reservoir with fresh brake fluid meeting the specification stamped on the reservoir cap (DOT 3 for this application) to the MAX line. Bleed the brake system completely following the factory-specified bleed sequence for this vehicle (typically starting with the wheel furthest from the master cylinder). Note: a complete bleed on ABS-equipped vehicles may require a scan tool to cycle the ABS/HCU. Ensure a firm pedal before proceeding. Top off reservoir as needed during bleeding.
    ⚠️A soft or spongy brake pedal indicates air in the system. The vehicle is unsafe to drive until brakes are properly bled and a firm pedal is achieved.

Reassembly

1. Reinstall any dash panels removed for access
2. Reconnect negative battery cable
3. Double-check all brake line connections for tightness and no leaks
4. Verify brake fluid level is at MAX line in reservoir

Verification

• Start the engine and let it idle. Listen for any vacuum leaks at the booster connection
• With engine running, press the brake pedal firmly and verify it feels solid with good assist. The pedal should not sink slowly to the floor
• Turn off the engine and pump the brake pedal several times. The pedal should become progressively harder with each pump
• Press and hold the brake pedal, then start the engine. The pedal should drop slightly when the engine starts, indicating booster vacuum assist is working
• Check all brake line connections for leaks with engine running and brake pedal applied
• Test drive in a safe area at low speed to verify proper brake operation before returning to normal use
• Recheck brake fluid level after test drive and top off if needed

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