Brake Booster Check Valve

Replace the brake booster check valve to restore proper vacuum-assisted braking function and eliminate brake pedal feedback issues.

Warnings

Tools required

Parts

• Brake booster check valve with grommet × 1 — Motorcraft CM-5191 or equivalent

Preparation

1. Park vehicle on level surface and apply parking brake
2. Turn ignition off and remove key
3. Allow engine to cool if recently operated (check valve is near hot engine components)
4. Open hood and secure with prop rod
5. Locate the brake booster on the driver's side firewall behind the master cylinder
6. Identify the vacuum hose connection on the front of the brake booster (large black rubber hose from intake manifold)

Procedure

1. 1

   Access the brake booster check valve
   Use a shop light to illuminate the area behind the brake master cylinder. The check valve is installed in the front center of the brake booster where the vacuum hose connects. On the 5.0L V8, access is from above on the driver's side. You may need to move wiring harnesses aside for better access.
2. 2

   Disconnect the vacuum hose
   Trace the vacuum hose from the intake manifold to the brake booster. At the booster connection, carefully pull the vacuum hose straight off the check valve. You may need to twist slightly while pulling. If the hose is stuck, use a flathead screwdriver to gently pry between the hose and the booster body, being careful not to damage the booster.
3. 3

   Remove the old check valve
   Grip the check valve body with needle-nose pliers and pull firmly straight out from the brake booster. The valve is retained by a rubber grommet and may require significant force. Use a twisting motion while pulling if needed. If the valve breaks, use pliers or a pick tool to remove any remaining pieces and the old grommet from the booster housing.
4. 4

   Inspect the booster port
   Examine the check valve port in the brake booster for cracks, damage, or debris. The port should be clean and smooth. Remove any old grommet material if it remained in the booster. Wipe the area clean with a dry cloth. Inspect the vacuum hose end for cracks or deterioration and replace if damaged.
5. 5

   Verify new check valve direction
   Identify the directional marking on the new check valve. The valve MUST be installed with the correct orientation: the end with the smaller diameter or the end marked with an arrow should point TOWARD the brake booster (into the booster housing). The larger diameter end connects to the vacuum hose. Hold the valve up to confirm you understand the correct orientation before installation.
6. 6

   Install new check valve with grommet
   If the grommet is separate, install it onto the check valve first, seating it in the groove. Position the check valve with the correct orientation (narrow end toward booster). Align the valve with the booster port and push firmly straight in until the grommet seats completely in the booster housing. You should feel it snap into place. The valve should be secure and not pull out easily.
7. 7

   Reconnect the vacuum hose
   Push the vacuum hose firmly onto the outer end of the check valve until it seats completely against the grommet. The hose should be fully engaged with no gaps visible. Tug on the hose to verify it is secure and will not pull off during normal operation.
8. 8

   Inspect all connections
   Visually verify the check valve is fully seated in the booster housing with no gaps around the grommet. Confirm the vacuum hose is properly connected to both the check valve and the intake manifold connection. Ensure no wiring or other components were disturbed during the repair. Reposition any moved wiring harnesses to their original locations.

Reassembly

1. No disassembly was required for this procedure
2. Ensure all vacuum connections are secure before testing

Verification

• Start the engine and listen for any vacuum leaks (hissing sounds) at the check valve connection. There should be no audible leaks
• With engine running, press the brake pedal multiple times. Pedal effort should be light and consistent with normal power-assisted braking
• Turn off the engine and wait 1 minute. Press the brake pedal - you should get 2-3 power-assisted pedal applications before the pedal becomes hard. This confirms the check valve is holding vacuum in the booster
• If using a vacuum pump: disconnect the vacuum hose and connect a vacuum pump to the check valve. Apply 20 inches Hg vacuum - it should hold for at least 30 seconds, confirming the check valve is sealing properly
• Road test the vehicle in a safe area at low speed. Verify normal brake pedal feel and adequate brake assist. If pedal is hard or requires excessive effort, STOP and recheck the installation immediately
• After test drive, recheck the vacuum hose connection to ensure it has not loosened

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