Brake Booster

Replacement of the vacuum brake booster assembly on a 1966 Chevrolet Corvette with 327ci V8, including master cylinder removal, booster mounting hardware, and vacuum line connections.

Warnings

Tools required

Parts

• Brake booster assembly (vacuum type) × 1 — Use OEM specification or Delco replacement
• Master cylinder to booster gasket × 1 — Use OEM specification
• Booster mounting nuts × 4 — 5/16"-18 or 3/8"-16 depending on application
• Vacuum check valve × 1 — Replace if damaged
• Brake fluid DOT 4 × 1 — Per fluid specification

Fluids

• DOT 4 Brake Fluid — 1 qt

Preparation

1. Park vehicle on level, stable surface and chock rear wheels securely
2. Disconnect negative battery cable to prevent accidental electrical shorts
3. Open hood and prop securely
4. Remove air cleaner assembly to improve access to master cylinder area
5. Place protective covering over fenders and cowl area to protect from brake fluid spills
6. Extract as much brake fluid as possible from master cylinder reservoir using turkey baster or fluid extraction syringe
7. Prepare clean containers to catch brake fluid during line disconnection
8. Apply penetrating oil to all visible brake line fittings and booster mounting nuts, allow to soak 15-20 minutes

Procedure

1. 1

   Disconnect brake lines from master cylinder
   Working from the engine compartment, identify the brake line connections at the master cylinder. The 1966 Corvette uses a dual master cylinder with two outlet ports. Using the appropriate flare nut wrench (typically 1/2" for front, 7/16" or 1/2" for rear), carefully loosen and remove the brake line fittings from the master cylinder. Have a catch pan ready as fluid will drain. Cap or plug the brake lines immediately with rubber caps or clean bolts wrapped in tape to prevent fluid loss and contamination. Mark the lines (front/rear) if not already obvious for correct reinstallation.
2. 2

   Remove master cylinder from brake booster
   Locate the two mounting nuts securing the master cylinder to the brake booster mounting studs. These are typically 1/2" or 9/16" nuts accessible from the engine compartment. Remove both nuts completely. Carefully pull the master cylinder straight forward off the booster mounting studs. The pushrod from the booster will disengage from the master cylinder piston. Set the master cylinder aside in a clean area where it will not tip over or leak onto painted surfaces. Inspect the pushrod for damage or excessive wear.
3. 3

   Disconnect vacuum hose from booster
   Locate the vacuum supply line connecting from the intake manifold to the brake booster check valve. The check valve is typically installed in the booster housing on the forward face. Using pliers if necessary, loosen and remove the hose clamp securing the vacuum hose to the check valve. Pull the vacuum hose off the check valve. Inspect the check valve; if it is damaged, corroded, or the internal check mechanism does not rattle when shaken, plan to replace it with the new booster or install a new valve.
4. 4

   Access booster mounting area from inside vehicle
   Move inside the vehicle to the driver's footwell area. You may need to remove the driver's side floor mat for better access and to protect it from dirt. Using a flashlight, locate the brake pedal assembly and the connection point where the brake pedal rod connects to the booster pushrod. This connection is typically at or near the top of the brake pedal arm.
5. 5

   Disconnect brake pedal pushrod
   Locate the clevis pin or retaining clip connecting the brake pedal arm to the booster pushrod. On 1966 Corvettes, this is typically secured with a cotter pin or spring clip and clevis pin. Remove the cotter pin or spring clip using pliers, then slide out the clevis pin to separate the brake pedal from the booster pushrod. The brake pedal will now move freely. Note the orientation and any bushings or washers on the clevis pin for reassembly.
6. 6

   Remove booster mounting nuts from firewall
   Still working from inside the vehicle, locate the four mounting nuts securing the brake booster to the firewall. These nuts are on studs that protrude through the firewall from the engine compartment side. The nuts are typically 9/16" or 5/8". Using an appropriately sized wrench or socket, remove all four mounting nuts completely. Keep these nuts if they are in good condition; otherwise use new hardware. Support the booster from the engine compartment side to prevent it from falling once the last nut is removed.
7. 7

   Remove old brake booster assembly
   Return to the engine compartment. With all mounting nuts removed, carefully pull the brake booster assembly straight back away from the firewall. The mounting studs will slide out of the firewall holes. Maneuver the booster assembly out of the engine compartment, being careful not to damage any surrounding components or wiring. The unit is bulky but not excessively heavy. Set the old booster aside for core return or disposal.
8. 8

   Inspect and clean mounting surfaces
   With the booster removed, inspect the firewall mounting surface for rust, damage, or deformation. Clean the firewall mounting area with a wire brush if needed. Inspect the four mounting studs on the new booster to ensure they are straight and threads are clean. Check that the pushrod on the new booster moves freely and that the internal spring returns it properly. Inspect the rubber grommet or seal around the studs where they pass through the firewall; replace if cracked or deteriorated.
9. 9

   Install new brake booster to firewall
   From the engine compartment, position the new brake booster assembly against the firewall, aligning the four mounting studs with the holes in the firewall. Push the booster firmly against the firewall until the studs protrude fully through to the interior side. Have an assistant verify from inside the vehicle that all four studs are protruding correctly and that the booster is seated flush against the firewall. If installing alone, you may need to secure one or two nuts finger-tight from inside to hold the booster in position.
10. 10

    Install and tighten booster mounting nuts
    Working from inside the vehicle, thread all four mounting nuts onto the studs and tighten them finger-tight initially. Then, working in a cross pattern (top left, bottom right, top right, bottom left), progressively tighten the nuts evenly. Tighten to a secure fit; typical specification for 5/16" studs is 15-20 ft-lbs, for 3/8" studs 20-25 ft-lbs. Do not overtighten as this can distort the firewall or damage the booster housing. Ensure the booster is pulled firmly and evenly against the firewall with no gaps.
11. 11

    Reconnect brake pedal pushrod
    Still inside the vehicle, align the brake pedal arm with the booster pushrod clevis. Insert the clevis pin through the pedal arm and clevis, ensuring any bushings or washers are in their original positions. Install the cotter pin or spring clip to secure the clevis pin. Verify the connection is secure by pulling on the brake pedal; it should have normal resistance and return freely. Verify there is no excessive play in the connection.
12. 12

    Connect vacuum line to booster
    Return to the engine compartment. If installing a new check valve, insert it into the booster vacuum port (typically on the front face of the booster) with the correct orientation (arrow on valve points toward booster). Push the vacuum supply hose onto the check valve nipple until it is fully seated. Install and tighten the hose clamp securely. Verify the vacuum hose has no cracks or damage and follows a path that avoids contact with hot engine components.
13. 13

    Install master cylinder gasket and position master cylinder
    Install a new gasket between the master cylinder and the brake booster mounting flange. Ensure the gasket is properly aligned with the mounting studs and the pushrod hole. Carefully position the master cylinder onto the booster mounting studs, guiding it over the pushrod. The pushrod should enter the rear of the master cylinder piston chamber. Push the master cylinder firmly onto the studs until it seats completely against the gasket and booster mounting flange.
14. 14

    Install master cylinder mounting nuts
    Thread both master cylinder mounting nuts onto the studs and tighten them evenly in an alternating pattern. Typical torque specification is 20-25 ft-lbs, but since no specific torque is provided for this vehicle, tighten firmly and evenly until the master cylinder is securely mounted with no movement. Do not overtighten as this can distort the master cylinder body or damage the mounting flange.
15. 15

    Reconnect brake lines to master cylinder
    Remove the caps or plugs from the brake lines. Thread the brake line fittings into the master cylinder ports by hand first, ensuring they start correctly and are not cross-threaded. The front line typically connects to the forward port, rear line to the rear port (verify against your earlier marking). Once hand-tight, use the flare nut wrench to tighten the fittings firmly. Typical specification is snug plus 1/4 to 1/2 turn, or approximately 12-15 ft-lbs for 3/8" fittings. Do not overtighten as this can damage the flare or strip the fitting.
16. 16

    Fill master cylinder reservoir
    Fill the master cylinder reservoir with fresh DOT 3 brake fluid (DOT 4 acceptable as an upgrade) to the appropriate level (typically 1/4" to 1/2" below the top of the reservoir). Use only clean fluid from a sealed container. Install the reservoir cap loosely. The fluid level will drop during the bleeding process.
17. 17

    Bleed brake system completely
    The entire brake system must be bled to remove all air introduced during this procedure. Begin by bleeding the wheel furthest from the master cylinder (typically right rear), then left rear, right front, left front. At each wheel, attach a clear hose to the bleeder valve, submerge the other end in a container of clean brake fluid. Have an assistant pump the brake pedal several times and hold pressure. Open the bleeder valve until fluid flows, then close it before the pedal reaches the floor. Repeat until no air bubbles appear in the fluid. Maintain master cylinder fluid level throughout the process. After bleeding all four wheels, the pedal should feel firm and high. If pedal remains soft or spongy, repeat bleeding process.
18. 18

    Check for leaks and verify booster operation
    With the engine off, inspect all brake line connections at the master cylinder for leaks. Wipe fittings dry and watch for fluid seepage while an assistant presses the brake pedal firmly. Start the engine and allow it to idle. Press and hold the brake pedal with firm pressure, then start the engine; the pedal should drop slightly under your foot as manifold vacuum reaches the booster (indicating booster vacuum assist is functioning). With the engine running, press and hold the brake pedal for 30 seconds; it should remain firm with no creep or sinking. If the pedal sinks, there is a leak or air in the system that must be corrected.

Reassembly

1. Reinstall air cleaner assembly
2. Top off master cylinder reservoir to proper level with DOT 4 brake fluid
3. Reconnect negative battery cable
4. Remove fender covers and clean any brake fluid residue immediately
5. Replace driver's side floor mat

Verification

• With engine off, pump brake pedal several times; it should build pressure and become firm
• Start engine; brake pedal should drop slightly as vacuum assist engages, then remain firm
• Perform a low-speed brake test in a safe area; vehicle should stop straight and smoothly with no pull
• Verify no brake fluid leaks at master cylinder connections or around booster seal
• Check brake pedal free play is correct (approximately 1/8" to 1/4" before resistance)
• Listen for vacuum leaks at booster hose connection with engine running
• Verify brake warning light does not illuminate on dash
• Perform full-pressure brake test in safe area before returning vehicle to service
• After first test drive, recheck all connections and fluid level; retighten if necessary

More procedures for this vehicle