Brake Master Cylinder

This procedure covers the removal and replacement of the brake master cylinder on a 2022 Rivian EDV 500, including brake fluid evacuation, hydraulic line disconnection, and system bleeding.

Warnings

Tools required

Parts

• Brake master cylinder assembly × 1 — Use OEM Rivian specification
• Master cylinder to booster gasket/seal × 1 — Use OEM specification
• Brake line crush washers (if equipped) × 4 — Use OEM specification

Fluids

• DOT 4 Brake Fluid — 1.5 qt

Preparation

1. Park vehicle on level ground and place wheel chocks behind rear wheels
2. Ensure vehicle is in PARK mode and power is OFF
3. Open hood and locate brake master cylinder on driver's side of engine bay near firewall
4. Disconnect 12V battery negative terminal and wait 2 minutes for system capacitors to discharge
5. Place absorbent pads under master cylinder area to protect components from brake fluid spills
6. Using turkey baster or fluid evacuator, remove as much brake fluid as possible from master cylinder reservoir to minimize spillage
7. Prepare clean workspace with all tools and new master cylinder within reach
8. Connect diagnostic scan tool and verify ability to enter brake service mode (required for proper bleeding)

Procedure

1. 1

   Disconnect electrical connector
   Locate the brake fluid level sensor electrical connector on the master cylinder reservoir. Press the locking tab and carefully disconnect the connector. Move it aside to prevent fluid contamination.
2. 2

   Remove reservoir cap and remaining fluid
   Remove the brake fluid reservoir cap. Use a turkey baster or fluid evacuator to remove all remaining brake fluid from the reservoir. Dispose of old fluid properly according to local regulations.
3. 3

   Disconnect brake lines from master cylinder
   Using a flare nut wrench to prevent rounding, carefully loosen the four brake line fittings at the master cylinder ports. There are typically two lines for the front circuit and two for the rear circuit. Once loosened, unthread by hand and immediately cap the open line ends with clean plastic plugs to prevent fluid loss and contamination. Position shop towels to catch residual fluid.
   ⚠Use only a flare nut wrench on brake line fittings. Standard open-end wrenches will round off the soft brass fittings and require line replacement.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
4. 4

   Remove master cylinder mounting nuts
   Locate the two master cylinder mounting nuts that secure the cylinder to the brake booster studs. Using a socket wrench, remove both nuts completely. Keep these nuts as they will be reused unless damaged.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
5. 5

   Remove master cylinder assembly
   Carefully pull the master cylinder straight away from the brake booster. The pushrod from the booster will separate from the master cylinder piston. Be prepared for residual brake fluid drips. Inspect the pushrod for damage and verify proper length (do not adjust unless specified by service manual).
6. 6

   Inspect and clean mounting surface
   Inspect the brake booster mounting surface and pushrod for damage, corrosion, or excessive wear. Clean the mounting surface with a clean, lint-free cloth. Inspect the old master cylinder gasket/seal and remove any remnants from the booster face. Verify pushrod moves freely and returns to proper position.
7. 7

   Prepare new master cylinder
   Remove the new master cylinder from packaging. Verify it matches the old unit in port configuration and mounting pattern. Install the new gasket/seal onto the rear of the master cylinder. Pre-fill the reservoir with fresh DOT 4 brake fluid to approximately half full to facilitate initial bleeding.
8. 8

   Bench bleed master cylinder (recommended)
   If possible, bench bleed the new master cylinder before installation. Thread short sections of brake line into the outlet ports, loop them back into the reservoir, and slowly stroke the piston with a large screwdriver until no air bubbles emerge. This significantly reduces air in the system and simplifies later bleeding. Remove bleed lines before installation.
9. 9

   Install master cylinder to brake booster
   Carefully align the master cylinder with the brake booster studs, ensuring the pushrod properly engages the piston in the master cylinder. Push the cylinder firmly against the booster mounting surface. Thread both mounting nuts onto the studs by hand to prevent cross-threading.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
10. 10

    Torque mounting nuts
    Using a torque wrench, tighten the master cylinder mounting nuts to 25.0 Nm (18.0 lb-ft) in a cross pattern. Verify the cylinder sits flush against the booster with no gaps.
    Torque spec

    Master Cylinder Nuts25 Nm (18 lb-ft)
11. 11

    Connect brake lines
    Remove the protective caps from the brake lines. If equipped with crush washers, install new washers on each line fitting. Carefully thread each brake line into its corresponding master cylinder port by hand, ensuring proper alignment to prevent cross-threading. Note the correct port assignments (typically outer ports for front circuit, inner ports for rear circuit, but verify with service documentation).
    ⚠Connecting brake lines to incorrect ports will cause improper brake balance and potential brake failure. Verify port assignments match factory configuration.
    Torque spec

    Brake Line Fittings15 Nm (11 lb-ft)
12. 12

    Torque brake line fittings
    Using a flare nut wrench and torque wrench, tighten each brake line fitting to 15.0 Nm (11.0 lb-ft). Do not overtighten as this can damage the fittings and cause leaks. Verify each fitting is secure and properly seated.
    Torque spec

    Brake Line Fittings15 Nm (11 lb-ft)
13. 13

    Fill brake fluid reservoir
    Fill the master cylinder reservoir with fresh DOT 4 brake fluid to the MAX level marking. Reconnect the fluid level sensor electrical connector, ensuring it clicks into place securely. Install the reservoir cap loosely (do not seal yet).
14. 14

    Bleed brake system
    Reconnect the 12V battery. Using a diagnostic scan tool, enter brake service mode to activate the ABS pump and open solenoid valves. Bleed the brake system in the proper sequence (typically: right rear, left rear, right front, left front, then ABS modulator if equipped). Use a pressure bleeder or two-person manual bleeding method. At each wheel, attach a clear tube to the bleeder valve, open the valve, and allow fluid to flow until no air bubbles are visible. Close the valve before releasing brake pedal pressure. Continuously monitor and refill the master cylinder reservoir to prevent introducing air. Continue until firm pedal is achieved.
    ⚠️Never allow the master cylinder reservoir to run empty during bleeding. This will introduce air and require restarting the entire bleeding process.
15. 15

    Final inspection and leak check
    With the system bled, fill the reservoir to the MAX mark and tighten the cap securely. Start the vehicle and verify the brake warning light extinguishes. With the vehicle still in PARK and chocks in place, firmly press the brake pedal multiple times. The pedal should be firm and not sink. Inspect all brake line connections at the master cylinder for any signs of leakage. Wipe all fittings clean and observe for 2-3 minutes while applying steady pedal pressure.

Reassembly

1. Verify all brake line fittings are torqued to specification and show no signs of leakage
2. Ensure master cylinder reservoir is filled to MAX level with fresh DOT 4 brake fluid and cap is secure
3. Confirm brake fluid level sensor connector is properly seated and locked
4. Verify no tools or materials are left in the engine bay
5. Clean any brake fluid residue from painted surfaces immediately with water

Verification

• With vehicle in PARK on level ground with wheel chocks, start the vehicle and verify brake warning light is OFF
• Press brake pedal firmly: pedal should be firm and high, with no sinking or sponginess. If pedal is soft, repeat bleeding procedure
• Perform a low-speed test drive in a safe area (empty parking lot): test brakes at 5 mph to verify proper function before proceeding to road speeds
• Verify even braking with no pulling to either side
• Test brake pedal feel at various speeds up to 25 mph in safe conditions
• After initial test drive, re-inspect all master cylinder connections for leaks while system is at operating pressure
• Check brake fluid level after test drive and top off if necessary
• If ANY abnormality is detected (soft pedal, pulling, warning lights, leaks), DO NOT DRIVE the vehicle and seek professional diagnosis immediately
• Schedule a follow-up inspection after 50-100 miles to verify no leaks have developed and pedal feel remains firm

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