Brake Booster Check Valve

This procedure replaces the brake booster check valve to restore proper vacuum retention and prevent loss of brake assist when the engine is off.

Warnings

Tools required

Parts

• Brake booster check valve × 1 — Use OEM Mopar check valve or quality aftermarket equivalent

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn ignition off and remove key
3. Allow engine to cool if recently operated
4. Open hood and secure with prop rod
5. Locate the brake booster on the driver side firewall behind the master cylinder
6. Identify the vacuum line connection and check valve on the front of the brake booster

Procedure

1. 1

   Locate brake booster check valve
   The brake booster is mounted on the firewall behind the master cylinder. The check valve is located on the front of the booster where the vacuum hose connects. On the 5.9L Cummins diesel, the brake booster vacuum is supplied by an engine-driven vacuum pump; trace the vacuum line from the vacuum pump on the engine to the brake booster on the driver side firewall. Confirm the exact vacuum pump location against the service manual for your vehicle.
2. 2

   Disconnect vacuum hose from check valve
   Grasp the vacuum hose firmly at the connection point on the brake booster. Pull straight away from the booster while twisting slightly to break the seal. The hose should slide off the check valve nipple. If the hose is stuck, use a flathead screwdriver to carefully pry between the hose and the booster, being careful not to damage the hose or booster housing.
3. 3

   Remove check valve from brake booster
   The check valve is pressed into a rubber grommet in the brake booster housing. Grasp the check valve body firmly and pull straight out from the booster. It may require significant force. Twist while pulling if necessary. If the valve is extremely difficult to remove, use needle nose pliers to grip the valve body, but pad the jaws to avoid damaging the valve if you intend to inspect it.
4. 4

   Inspect old check valve and grommet
   Examine the old check valve for cracks, deterioration, or damage. Test it by attempting to blow through it in both directions - it should allow air flow in one direction only, permitting air to be drawn out of the booster toward the vacuum source, and block flow in the reverse direction back into the booster. Inspect the rubber grommet in the booster housing for cracks, hardening, or deterioration. If the grommet is damaged, it must be removed and replaced. Use needle nose pliers to extract a damaged grommet.
5. 5

   Install new check valve grommet if needed
   If the grommet was removed or is being replaced, press the new grommet into the brake booster housing opening. Ensure it seats fully and evenly in the housing bore. The grommet should be flush with or slightly below the booster housing surface.
6. 6

   Verify new check valve orientation and operation
   Before installation, verify the new check valve operates correctly by blowing through it. It should allow air flow in one direction only. Identify the correct installation orientation - the booster side of the valve is the end that permits air to be evacuated out of the booster toward the vacuum source, while blocking reverse flow back into the booster. Most check valves have an arrow indicating flow direction toward the vacuum source; the arrow must point away from the booster toward the vacuum pump. Note this orientation carefully.
7. 7

   Install new check valve into booster
   Insert the new check valve into the grommet in the brake booster housing with the correct orientation - the valve must allow vacuum to enter the booster but prevent it from escaping. Push the valve firmly into the grommet until it seats completely. The valve should be firmly retained by the grommet and should not pull out easily.
8. 8

   Reconnect vacuum hose
   Push the vacuum hose onto the check valve nipple firmly until it bottoms out. Ensure the connection is secure and the hose is fully seated on the valve. Tug on the hose to verify it is properly retained. Inspect the vacuum hose for cracks, deterioration, or damage and replace if necessary.
9. 9

   Inspect entire vacuum system
   Trace the vacuum line from the engine-mounted vacuum pump to the brake booster, inspecting for cracks, loose connections, or damage. Check the vacuum pump belt for proper tension and condition. Verify all connections are secure.

Reassembly

1. Close hood and ensure it latches properly
2. No disassembly was required beyond the check valve removal

Verification

• Start the engine and allow it to reach normal idle speed. Listen for any vacuum leaks (hissing sounds) around the brake booster area
• With engine running, press the brake pedal several times. The pedal should feel light and easy to press with normal brake assist present
• With engine running, press and hold the brake pedal, then shut off the engine. The pedal should remain in position and not slowly sink, indicating the check valve is holding vacuum
• Wait 1-2 minutes after engine shutdown, then press the brake pedal. You should feel power assist for at least 1-2 pedal applications as stored vacuum is depleted. This confirms the check valve is retaining vacuum
• After vacuum is depleted (engine off), the brake pedal should become noticeably harder but brakes should still function - this is normal without power assist
• CRITICAL: Perform a low-speed test drive in a safe area. Verify brake assist is present and braking performance is normal. If pedal feel is abnormal or stopping distances seem increased, DO NOT DRIVE and seek professional service immediately
• After test drive, recheck all vacuum connections for leaks and proper seating

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