Replacement of the brake master cylinder on a 2024 Tesla Model 3 Long Range. This job requires fluid evacuation from the reservoir, careful disconnection of brake lines from the master cylinder, and a full brake bleed afterward — Tesla's iBooster-style integrated brake system makes this more involved than a traditional ICE master cylinder.

Warnings

Tools required

Parts

• Brake master cylinder assembly (manufacturer-specified for 2024 Model 3 LR AWD) × 1 — Refer to Tesla EPC for current part number
• Master cylinder reservoir seal / grommet kit (if supplied separately) × 1 — OEM seal kit
• Brake line crush washers / sealing washers (if applicable to fittings) × 2 — OEM sealing washers

Fluids

• DOT 4 Brake Fluid (Tesla specification — note: do not use DOT 3 despite generic database listing; Tesla Model 3 specifies DOT 4) — 1 qt

Preparation

1. Park on level ground, place in P, engage parking brake.
2. Exit ALL doors with key fob away from the vehicle. Wait at least 2 minutes for HV systems to fully de-energize, even on this non-HV job.
3. Disconnect the 12V low-voltage battery. On 2024 Model 3, this is located behind the right rear seat back panel (or under the floor on later lithium 12V variants — verify before cutting power). Remove the cover and disconnect the negative terminal first.
4. DO NOT touch, cut, or pierce ANY orange cable — these are high-voltage and lethal.
5. If at any point you encounter an orange cable, an HV component, or are unsure if a system is de-energized: STOP and consult a Tesla-certified technician.
6. Open the frunk and remove the frunk liner / cowl trim as needed to access the brake master cylinder and reservoir on the driver-side firewall area.
7. Place fender covers over both front fenders and cover any painted surfaces under the work area.
8. Have a catch pan and absorbent rags positioned beneath the master cylinder before disconnecting any brake lines.
9. Confirm replacement master cylinder matches the OEM unit by part number before beginning.

Procedure

1. 1

   Evacuate brake fluid reservoir
   Remove the reservoir cap and use a clean fluid evacuator or vacuum syringe to extract as much brake fluid as possible from the reservoir. Dispose of used fluid properly — do not reuse.
   ⚠Brake fluid absorbs moisture rapidly. Keep the new fluid container sealed until ready to refill.
2. 2

   Disconnect electrical connectors from the brake booster / master cylinder assembly
   Locate the low-voltage connectors on the electric brake booster body. Release the locking tabs and disconnect each connector. Note routing for reinstallation. Do not pull on wires — grip the connector body only.
   ⚠If any connector appears orange or thicker than typical signal wiring, STOP and verify — do not disconnect HV-rated connectors.
3. 3

   Disconnect the reservoir from the master cylinder (if separable)
   If the fluid reservoir is a separate piece mounted to the master cylinder via grommets, disconnect any low-fluid sensor connector and gently pull the reservoir upward to release it from its grommets. Some Model 3 units have an integrated reservoir — in that case, leave it attached and remove as an assembly.
4. 4

   Disconnect brake lines from the master cylinder
   Using a properly sized line wrench (flare nut wrench), carefully loosen each hydraulic brake line fitting at the master cylinder. Support the line to avoid bending. Cap each line immediately with a clean plug or wrap with a clean rag to prevent contamination and excessive fluid loss. Note the position of each line for reinstallation.
   ⚠Do not use an open-end wrench — it will round the soft fitting nuts. A line/flare wrench is mandatory.
   ⚠Brake fluid will drip — protect the aluminum subframe and any painted surfaces below.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
5. 5

   Remove master cylinder mounting nuts
   Locate the master cylinder mounting nuts that secure the assembly to the brake booster (or to the firewall bracket, depending on configuration). Loosen each nut evenly in a cross pattern, then remove fully. Support the master cylinder while removing the last nut.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
6. 6

   Remove the master cylinder
   Carefully pull the master cylinder straight off its mounting studs. Be prepared for residual fluid. Place the unit in a catch pan and inspect the mounting surface for debris, old gasket material, or fluid residue. Clean the booster mounting face with a lint-free rag.
   ⚠Do not allow brake fluid to drip onto the booster electronic seal area or any nearby connectors.
7. 7

   Bench-bleed the new master cylinder
   Mount the new master cylinder in a soft-jaw vise. Install the manufacturer-supplied bench-bleed kit (or fabricate using short lines that loop fluid back into the reservoir ports). Fill the reservoir with fresh DOT 4 brake fluid and slowly stroke the pushrod with a blunt tool until no air bubbles are visible exiting the bleed lines. This step is essential to prevent air ingestion into the iBooster.
   ⚠Skipping the bench bleed will likely require a dealer-level diagnostic bleed routine to recover.
8. 8

   Install the new master cylinder
   Position the new master cylinder onto the booster mounting studs. Hand-thread each mounting nut, then torque evenly in a cross pattern to specification.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
9. 9

   Reconnect brake lines
   Thread each brake line fitting into the master cylinder by hand first to avoid cross-threading. Once started, snug with a line wrench, then torque to specification. Verify each line is in its correct port per your earlier notes.
   ⚠Cross-threading the soft fitting will require master cylinder replacement again. Always start by hand.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
10. 10

    Reinstall reservoir (if removed separately) and reconnect electrical connectors
    Lubricate new reservoir grommets with fresh brake fluid, press the reservoir firmly into place, and reconnect the fluid level sensor connector. Reconnect all booster electrical connectors, ensuring locking tabs fully engage.
11. 11

    Fill reservoir and perform initial manual bleed
    Fill the reservoir with fresh DOT 4 brake fluid to the MAX line. Perform a manual or pressure bleed at each caliper in the manufacturer-recommended sequence (typically furthest from master cylinder first). Maintain reservoir level above MIN throughout. Torque each bleeder screw after bleeding.
    ⚠Never let the reservoir drop below the MIN mark during bleeding — this will introduce air into the booster.
12. 12

    Reconnect 12V battery and run scan tool brake bleed sequence
    Reconnect the 12V negative terminal. Wake the vehicle and connect a scan tool capable of executing the Tesla automated brake bleed routine. Run the routine, which actuates the iBooster and ABS valves to purge air from internal passages. Repeat the manual caliper bleed after the automated routine to capture any newly released air.
    ⚠️Without the scan tool routine, trapped air in the iBooster can cause a significantly degraded or delayed brake response.
13. 13

    Top off and seal reservoir
    Top off the reservoir to the MAX line with fresh DOT 4 fluid. Install the reservoir cap hand-tight to specification.

Reassembly

1. Reinstall any frunk liner, cowl trim, or covers removed for access.
2. Verify all electrical connectors are fully seated and locked.
3. Wipe down the entire master cylinder area with clean water to remove any brake fluid residue, then dry.
4. Confirm 12V battery cover and any removed seat-back trim (if 12V was accessed there) is properly reinstalled.
5. Close the frunk and verify latching.

Verification

• With the vehicle awake, press the brake pedal multiple times — pedal should feel firm and consistent, not spongy or sinking.
• Verify NO brake-related warnings are present on the center display (ABS, ESC, regen disabled, brake assist faults, etc.). Any persistent warning indicates the bleed procedure was incomplete.
• Inspect all brake line fittings and the master cylinder mounting flange for any sign of weeping after 5 minutes of pedal pressure.
• Test drive at low speed in a safe area: confirm normal pedal travel, no pulling, and that regenerative + friction braking blend feels normal.
• After the test drive, re-inspect for leaks and check reservoir level — top off if needed.
• Reset the brake fluid service interval — Tesla recommends DOT 4 brake fluid replacement every 2 years regardless of mileage; record this service date for the next interval.

More procedures for this vehicle