Brake Booster

This procedure replaces the brake booster on a 2015-2020 Ford F-150 with 5.0L V8 engine, including master cylinder removal, vacuum line disconnection, and brake system bleeding.

Warnings

Tools required

Parts

• Brake booster assembly × 1 — Use OEM specification
• Master cylinder to booster gasket/seal × 1 — Usually included with booster
• Brake booster mounting nuts × 4 — Reuse if not damaged
• Brake booster pushrod clip × 1 — Reuse if not damaged

Fluids

• Motorcraft DOT 4 LV Brake Fluid — 1 qt

Preparation

1. Park vehicle on level surface and engage parking brake. Place wheel chocks behind rear wheels.
2. Disconnect negative battery terminal and wait 2 minutes for airbag system to discharge.
3. Remove engine cover if equipped by pulling upward on retaining clips.
4. Open driver's door and remove lower dash trim panel below steering column using trim removal tools.
5. Remove as much brake fluid as possible from master cylinder reservoir using turkey baster or fluid pump to minimize spillage.
6. Place protective covering over front fender and firewall area to protect paint from brake fluid.
7. Prepare clean workspace for removed master cylinder - brake fluid will drain from it.

Procedure

1. 1

   Disconnect brake lines from master cylinder
   Locate the two brake line fittings on the side of the master cylinder. Use appropriate size line wrench (NOT standard wrench) to loosen each fitting. Turn counterclockwise approximately 1-2 turns to break seal. Have shop towels ready to catch draining fluid. Once both fittings are loose, cap or plug the brake lines with rubber caps or clean rags to prevent contamination and further fluid loss.
   ⚠Use only line wrenches on brake fittings. Standard wrenches will round off the soft metal fittings and cause leaks or require line replacement.
2. 2

   Remove master cylinder from brake booster
   Disconnect the electrical connector from the brake fluid level sensor on top of the master cylinder reservoir. Remove the two nuts securing the master cylinder to the brake booster studs using a socket wrench. Carefully pull the master cylinder straight forward off the booster studs. Have a container ready as residual fluid will drain from the rear of the cylinder. Set master cylinder aside in prepared clean area. Do not allow brake fluid to contact painted surfaces.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
3. 3

   Disconnect vacuum line from brake booster
   Locate the vacuum hose connection on the front of the brake booster (connects to intake manifold). Squeeze or release the hose clamp using pliers and slide it back along the hose. Twist the vacuum hose gently while pulling to disconnect it from the booster check valve. Inspect the check valve - it should remain in the booster. If check valve comes out with hose, reinstall it into the new booster before installation.
4. 4

   Access brake pedal pushrod connection from inside cab
   From inside the vehicle under the dash, locate the brake pedal arm and the booster pushrod connection point. Use a flashlight to clearly see the connection. The pushrod is connected to the brake pedal arm with a clevis pin retained by a clip. Identify the retaining clip style (may be hairpin or spring clip depending on production date).
5. 5

   Disconnect pushrod from brake pedal
   Using needle-nose pliers or appropriate tool, remove the retaining clip from the clevis pin connecting the pushrod to the brake pedal arm. Slide the clevis pin out to separate the pushrod from the pedal. The pin may be tight - do not use excessive force that could damage the pedal assembly. Keep the clip and pin for reinstallation (unless new hardware came with replacement booster). Allow the pushrod to hang free.
   ⚠Do not lose the clevis pin retaining clip. Replacement clips must be the correct type for safe pedal retention.
6. 6

   Remove brake booster mounting nuts
   From the engine compartment side, locate the four mounting nuts that secure the brake booster to the firewall. These nuts are accessed from the engine bay and thread onto studs that pass through the firewall. Using appropriate socket and extension, remove all four mounting nuts. Support the booster with one hand while removing the final nut to prevent it from falling.
   Torque spec

   Brake Booster Nuts25 Nm (18 lb-ft)
7. 7

   Remove brake booster from vehicle
   From the engine compartment, carefully pull the brake booster assembly forward off the mounting studs. The pushrod will come through the firewall from the cab side. Maneuver the booster out of the engine bay, being careful not to damage any surrounding components or wiring. The booster is bulky but not extremely heavy (approximately 10-15 lbs). Inspect the firewall mounting area for any corrosion or damage.
8. 8

   Prepare new brake booster for installation
   Compare the new booster to the old unit to verify correct replacement part. Check that the check valve is installed in the new booster (transfer from old unit if necessary). Inspect the master cylinder mounting surface on the new booster and install new gasket/seal if provided. Verify pushrod length matches the old unit - incorrect pushrod length will cause brake drag or excessive pedal travel. Measure from booster mounting face to end of pushrod and compare.
   ⚠️Incorrect pushrod length will cause either brake drag (too long) or excessive pedal travel/reduced braking (too short). Verify pushrod adjustment before installation.
9. 9

   Install new brake booster to firewall
   From engine compartment, carefully position the new brake booster to the firewall, guiding the pushrod through the firewall opening into the cab. Align the four mounting studs with the holes in the firewall. From engine bay, start all four mounting nuts by hand to ensure proper thread engagement. Tighten the nuts in a cross pattern (opposite corners) using a torque wrench to specification. Do not overtighten as this can distort the booster housing.
   ⚠Tighten mounting nuts in cross pattern to ensure even sealing and prevent housing distortion.
   Torque spec

   Brake Booster Nuts25 Nm (18 lb-ft)
10. 10

    Reconnect pushrod to brake pedal
    From inside the cab, align the pushrod clevis with the brake pedal arm hole. Insert the clevis pin through the pedal arm and pushrod clevis. Install the retaining clip fully onto the clevis pin, ensuring it is properly seated and cannot fall out. Verify the connection is secure by gently pulling on the pedal - there should be no play in the connection. If equipped with adjustable pushrod lock nut, verify it is tight to specification.
    Torque spec

    Brake Pedal Pushrod Lock15 Nm (11 lb-ft)
11. 11

    Connect vacuum line to brake booster
    From engine compartment, push the vacuum hose firmly onto the booster check valve until it seats completely. Slide the hose clamp into position over the connection point (approximately 1/2 inch from end of hose). Ensure the clamp is tight and the hose cannot be pulled off by hand. Verify the other end of the vacuum line is properly connected to the intake manifold.
12. 12

    Install master cylinder to brake booster
    Inspect the master cylinder pushrod contact area and clean if necessary. Verify the gasket/seal is properly positioned on the booster mounting face. Carefully align the master cylinder with the booster studs and push it straight onto the studs until it seats against the booster. Install the two mounting nuts and tighten in a cross pattern to specification using a torque wrench. Reconnect the brake fluid level sensor electrical connector.
    Torque spec

    Master Cylinder Nuts25 Nm (18 lb-ft)
13. 13

    Reconnect brake lines to master cylinder
    Remove the protective caps or rags from the brake line ends. Thread each brake line fitting into the master cylinder ports by hand first to ensure proper thread engagement and prevent cross-threading. Once both fittings are hand-tight, use a line wrench to tighten each fitting to specification. Do not overtighten as this can damage the fittings. Wipe away any spilled brake fluid immediately.
    ⚠Cross-threading brake line fittings will cause leaks and require line replacement. Always start fittings by hand first.
    Torque spec

    Line Fittings26 Nm (19 lb-ft)
14. 14

    Fill and bleed brake system
    Fill the master cylinder reservoir with fresh DOT 4 LV brake fluid to the MAX line. Bleed the brake system using proper sequence: right rear, left rear, right front, left front. Use a vacuum pump or pressure bleeder for best results. Pump brake pedal and hold, then open bleeder screw at each wheel until fluid runs clear with no air bubbles. Close bleeder before releasing pedal. Repeat until pedal is firm. Keep reservoir filled throughout bleeding process. After bleeding all wheels, tighten all bleeder screws to specification.
    ⚠️Never allow master cylinder reservoir to run empty during bleeding or additional air will enter the system requiring complete re-bleeding.
    Torque spec

    Bleeder Screw16 Nm (12 lb-ft)
15. 15

    Reinstall interior and engine compartment components
    Reinstall the lower dash trim panel under the steering column, ensuring all clips are properly seated. Reinstall engine cover if equipped by pressing down on mounting points until clips engage. Reconnect the negative battery terminal. Check the master cylinder reservoir fluid level and top off to MAX line if needed. Inspect all connections for leaks.

Reassembly

1. Ensure all four brake booster mounting nuts are torqued to specification in cross pattern
2. Verify brake pedal pushrod clevis pin retaining clip is fully seated and secure
3. Confirm vacuum hose is properly connected to booster with clamp positioned correctly
4. Double-check both brake line fittings are torqued to specification with no leaks
5. Verify master cylinder reservoir is filled to MAX line with correct DOT 4 LV fluid
6. Ensure all interior trim panels are properly reinstalled and secured

Verification

• With engine off, pump brake pedal several times. Pedal should become firm and hold pressure. Soft or spongy pedal indicates air in system - re-bleed if necessary.
• Start engine and verify brake pedal does not sink. Pedal should drop slightly when engine starts (vacuum assist engaging) then remain firm.
• Check for brake fluid leaks at master cylinder, all brake line connections, and all four wheel bleeder screws. No fluid should be visible.
• Test drive in safe area at low speed. Brake pedal should feel firm with normal travel distance. Brakes should apply evenly without pulling to either side.
• Perform several moderate stops from 30 mph to verify proper brake function and pedal feel before returning to normal driving.
• After test drive, recheck master cylinder fluid level and inspect all connections again for leaks.
• Verify ABS warning light is not illuminated on dashboard. If illuminated, scan for codes as system may require additional bleeding with scan tool.

Related trouble codes on this vehicle

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