Brake Master Cylinder

This procedure covers the removal and replacement of the brake master cylinder on a 2024 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 mounting nuts × 2 — Reuse unless damaged
• Brake line crush washers/seals × 4 — Replace all sealing surfaces

Fluids

• DOT 4 Brake Fluid — 1.5 qt

Preparation

1. Park vehicle on level ground and apply parking brake firmly
2. Place wheel chocks behind rear wheels
3. Disconnect 12V battery negative terminal and wait 5 minutes for system capacitors to discharge
4. If equipped, follow Rivian service manual HV disconnect procedures to isolate high-voltage system
5. Open driver's door to access brake pedal from interior
6. Protect surrounding painted surfaces and wiring harnesses with plastic sheeting or towels
7. Ensure adequate ventilation in work area due to brake fluid vapors
8. Have brake fluid catch container positioned under master cylinder area

Procedure

1. 1

   Remove brake fluid from reservoir
   Use a vacuum pump or clean turkey baster to remove as much brake fluid as possible from the master cylinder reservoir. This minimizes spillage during removal. Dispose of old brake fluid according to local regulations. Do not reuse old brake fluid.
2. 2

   Disconnect brake line fittings
   Locate all brake line fittings on the master cylinder (typically 4 lines for dual-circuit system). Using the appropriate size flare nut wrench, carefully loosen each brake line fitting. Work slowly to avoid rounding the fittings. Have catch container ready as fluid will drain from lines. Once loosened, unthread fittings by hand and immediately cap or plug open lines to prevent contamination and further fluid loss.
   ⚠Use only a flare nut wrench on brake line fittings. Standard wrenches will round the soft brass fittings, requiring line replacement.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
3. 3

   Disconnect electrical connectors
   Locate the brake fluid level sensor connector on the master cylinder reservoir. Press the locking tab and carefully disconnect the electrical connector. On EDV models, there may be an additional connector for the electronic brake boost system - disconnect this as well. Note connector orientation for reinstallation.
4. 4

   Access master cylinder mounting nuts
   Working from inside the vehicle at the brake pedal assembly, locate the master cylinder pushrod connection and mounting nuts. You may need to remove the lower dashboard trim panel for access. The master cylinder is mounted to the brake booster or electronic brake actuator assembly with 2 mounting nuts accessible from inside the cabin.
5. 5

   Remove pushrod retaining clip
   Locate the pushrod retaining clip that connects the master cylinder pushrod to the brake pedal arm. Use needle-nose pliers to compress and remove the retaining clip. Carefully slide the pushrod off the brake pedal pivot pin. Note the orientation and position of any spacers or bushings.
6. 6

   Remove master cylinder mounting nuts
   Using the appropriate socket, remove the 2 master cylinder mounting nuts from inside the vehicle. Support the master cylinder from the engine compartment side as you remove the final nut. Carefully pull the master cylinder forward to disengage it from the mounting studs. Have rags ready to catch any remaining fluid.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
7. 7

   Remove master cylinder assembly
   Carefully maneuver the master cylinder out of the engine compartment, taking care not to spill remaining fluid on painted surfaces or wiring. Inspect the mounting surface on the brake booster/actuator for damage or contamination. Clean the mounting surface thoroughly with brake cleaner and lint-free rags.
8. 8

   Prepare new master cylinder
   Remove the new master cylinder from packaging. Verify it matches the original unit exactly, including reservoir configuration and line port positions. Bench bleed the new master cylinder before installation: Fill the reservoir with fresh DOT 4 fluid, use bleeder fittings or return tubes, and slowly stroke the pushrod until fluid flows from all ports without air bubbles. This critical step prevents introducing large air pockets into the brake system.
9. 9

   Install new master cylinder
   Position the new master cylinder onto the mounting studs from the engine compartment side, ensuring the pushrod properly engages with the brake booster/actuator. From inside the vehicle, start both mounting nuts by hand to ensure proper thread engagement. Thread nuts several turns by hand before using tools.
   Torque spec

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

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

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

    Reconnect pushrod to brake pedal
    Align the pushrod with the brake pedal pivot pin, ensuring any spacers or bushings are in their original positions. Install the retaining clip, ensuring it is fully seated and secure. Verify the pushrod moves freely when the brake pedal is depressed.
12. 12

    Connect brake lines
    Remove caps or plugs from brake lines. Install new crush washers/seals on each brake line fitting. Thread each brake line fitting into the master cylinder by hand for several turns to ensure proper alignment and prevent cross-threading. Using a flare nut wrench and torque wrench, tighten each fitting to 15.0 Nm (11.0 lb-ft). Tighten fittings in sequence rather than fully torquing one at a time.
    ⚠Cross-threading brake line fittings will require replacement of lines and/or master cylinder. Always start fittings by hand and verify smooth threading.
    Torque spec

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

    Reconnect electrical connectors
    Reconnect the brake fluid level sensor connector to the master cylinder reservoir. Ensure the locking tab clicks into place. If equipped, reconnect the electronic brake boost system connector. Verify all connections are secure.
14. 14

    Fill reservoir and bleed brake system
    Fill the master cylinder reservoir to the MAX line with fresh DOT 4 brake fluid. Perform a complete brake system bleeding procedure following Rivian specifications: Start with the wheel furthest from the master cylinder (typically right rear), then left rear, right front, and left front. Use a pressure bleeder or two-person manual bleeding method. Continue bleeding each corner until fluid runs clear with no air bubbles. Maintain reservoir level above MIN line throughout bleeding process. On EDV models with brake-by-wire, you may need a scan tool to activate the ABS pump and bleed the hydraulic control unit.
    ⚠️Incomplete bleeding will result in a soft brake pedal and reduced braking performance. All air must be removed from the system before operating the vehicle.
15. 15

    Check for leaks and test brake pedal
    With the reservoir filled to the MAX line, inspect all brake line fittings at the master cylinder for leaks. Have an assistant press the brake pedal firmly and hold while you inspect. Look for any fluid seepage at fittings. Test brake pedal feel - it should be firm with no excessive travel. If pedal feels soft or sinks slowly, repeat bleeding procedure. Fill reservoir to MAX line as final step.

Reassembly

1. Reinstall any dashboard trim panels removed for access to the master cylinder
2. Reconnect 12V battery negative terminal
3. If HV system was disconnected, follow Rivian reconnection and verification procedures
4. Remove wheel chocks and protective coverings from painted surfaces
5. Clean any brake fluid spills immediately with water

Verification

• Start the vehicle and verify the brake warning light extinguishes after a few seconds (normal system check)
• Check for any warning messages on the instrument cluster related to brake system, ABS, or stability control
• With engine running, press brake pedal firmly - it should feel solid with minimal travel and no sinking
• Perform a low-speed brake test in a safe area to verify normal braking function before road use
• Recheck brake fluid level after test drive and top off if necessary to MAX line
• Inspect all brake line fittings at master cylinder for any signs of leakage
• Verify brake pedal does not sink when held under firm pressure for 30 seconds
• If vehicle is equipped with regenerative braking display, verify normal operation and integration with hydraulic brakes
• Test ABS function in a safe area if conditions permit to ensure hydraulic control unit was properly bled

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