Brake Booster Check Valve

Replace the brake booster check valve to restore proper vacuum-assist brake operation and prevent hard brake pedal or loss of power assist.

Warnings

Tools required

Parts

• Brake booster check valve × 1 — Use OEM specification
• Vacuum hose (if damaged) × 1 — 3/8" ID vacuum-rated hose

Preparation

1. Park vehicle on level ground and apply parking brake
2. Turn ignition OFF and remove key
3. Allow engine to cool if recently running (at least 15 minutes)
4. Open hood and secure with prop rod
5. Locate brake booster on firewall (driver side, large black or cadmium-plated canister behind master cylinder)
6. Identify vacuum hose running from intake manifold to front of brake booster

Procedure

1. 1

   Locate the check valve
   The check valve is installed in the front center of the brake booster housing where the vacuum hose connects. It is a small cylindrical valve (approximately 1.5 inches long) that fits into a rubber grommet in the booster. The vacuum hose supplying manifold vacuum connects to the outer end of the check valve. Note: on some early Ford applications the check valve is an inline unit within the vacuum hose rather than grommet-mounted in the booster face — verify your configuration before removal. Use the flashlight to clearly identify the valve and its orientation before removal.
2. 2

   Disconnect vacuum hose from check valve
   Grasp the vacuum hose firmly near the connection point to the check valve. Twist the hose back and forth while pulling straight away from the valve to break the seal. If the hose is stuck, use a flathead screwdriver to carefully pry between the hose and valve body, being careful not to damage the hose. Inspect the hose end for cracks, hardening, or damage.
3. 3

   Remove check valve from booster
   Firmly grasp the check valve body with your hand. Twist the valve back and forth slightly while pulling straight out from the booster housing to break the grommet seal. The valve is retained by a rubber grommet and may require significant force to remove. If stuck, use needle-nose pliers to grip the valve body (not the vacuum hose nipple) and twist while pulling. The rubber grommet may come out with the valve or remain in the booster housing. Verified detail (Check valves in brake boosters from this era typically do not have a twist-lock mechanism requiring counterclockwise rotation. They are friction-fit into a rubber grommet and pull straight out without twisting.): Firmly grasp the check valve body with your hand and pull straight out from the booster housing. The valve is retained by a rubber grommet and may require significant force to remove.
4. 4

   Inspect and remove grommet
   If the rubber grommet remained in the booster housing, use needle-nose pliers or a small flathead screwdriver to carefully extract it. Inspect the grommet for cracks, tears, hardening, or deterioration. The grommet provides the vacuum seal, so it must be in good condition. If damaged, it should be replaced with the new check valve assembly (most replacement valves include a new grommet).
5. 5

   Inspect old check valve
   Examine the old check valve for the direction of the arrow or flow marking on the valve body (if present). The valve allows air to flow in only one direction: FROM the booster toward the intake manifold, so the booster is evacuated. It blocks reverse flow, trapping vacuum in the booster when manifold vacuum drops. Attempt to blow air through the valve in both directions to verify failure: a good valve blocks airflow blown toward the booster but passes air blown from the booster side toward the manifold. A failed valve allows flow in both directions or no flow at all.
6. 6

   Prepare new check valve
   Remove new check valve from packaging and verify it matches the old valve in size and configuration. If a new grommet is included, install it onto the check valve body (the end that inserts into the booster, not the hose connection end). Ensure the grommet is seated fully in the groove on the valve body. Verify correct valve orientation by function rather than any printed arrow: the valve must allow air to be drawn from the booster toward the manifold, while blocking reverse flow back into the booster. Install the larger grommet end into the booster and the hose nipple facing the manifold hose.
7. 7

   Install new check valve into booster
   Align the new check valve with the opening in the brake booster housing. The valve installs with the large grommet end into the booster, and the smaller vacuum hose nipple facing outward toward the engine. Push the valve straight into the housing with firm hand pressure until the grommet seats completely and the valve is flush with the booster face. The valve is retained by friction fit in the rubber grommet. Verified detail (Grommet-style check valves on this era Ford are pressed straight in and held by the rubber grommet, not locked with tabs. The conditional 'if equipped' is acceptable but the locking-tab implication is likely inapplicable to this vehicle.): Ensure the grommet is fully seated so the valve is retained securely; these grommet-mounted valves are held by friction and do not require a twist-lock action.
8. 8

   Reconnect vacuum hose
   Inspect the vacuum hose end again for damage. If cracked or hardened, cut off 1/2 inch of hose to expose fresh rubber, or replace the entire hose. Push the vacuum hose straight onto the check valve nipple until it is fully seated (approximately 1 inch onto the nipple). The hose should fit snugly with no gaps. If the hose is loose, replace it with new 3/8-inch ID vacuum-rated hose.

Reassembly

1. No disassembly was required beyond component removal
2. Ensure vacuum hose has no kinks or sharp bends between intake manifold and booster
3. Verify all vacuum connections are secure with no loose fittings

Verification

• Start engine and let idle. Listen for hissing sounds at the booster or check valve indicating a vacuum leak. There should be no audible air leaks
• With engine running, press brake pedal and verify normal power-assist operation. Pedal should depress smoothly with moderate pressure, not feel hard or require excessive force
• Turn engine OFF and wait 5 seconds. Press brake pedal 2-3 times. The first application should feel power-assisted (soft), subsequent applications should gradually become harder as stored vacuum depletes. This confirms the check valve is holding vacuum
• Restart engine and verify brake pedal drops slightly when engine starts, confirming vacuum assist has been restored
• Perform a low-speed test drive in a safe area and verify normal brake operation with no hard pedal or loss of assist
• Recheck vacuum hose connection after test drive to ensure it has not worked loose

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