G300 - Bleeding and flushing brakes

Here is a good description of the process you need:

On a W463 G300 with conventional ABS (not SBC), Mercedes’ workshop procedure is AR42.10-P-0010GG. The factory method is a pressure bleed at 2.0 bar, not just pumping the pedal. ABS can trap air in the hydraulic unit; if the pedal stays spongy after a normal bleed, you need a scan tool to cycle the pump.

Fluid and specs

• Use DOT 4 only (never mix DOT 5 silicone).
• Keep the reservoir topped up the whole time. Never let it run dry.
• Bleed pressure: 2.0 bar (~29 psi).
• Bleed-screw torque: front fixed caliper 14 Nm, rear floating caliper 15 Nm.
• Per bleed screw, Mercedes typically wants about 80 cm³ of clean, bubble-free fluid.

Tools

• Pressure bleeder with the correct Mercedes reservoir adapter
• Fresh DOT 4
• Clear hose and catch bottle
• Correct bleeder wrench (often 7–11 mm depending on caliper)
• Jack stands / wheel chocks
• Optional: STAR/Xentry or another bidirectional scanner with ABS/ESP bleed / pump activation

Preparation

1. Park level, chock wheels, ignition off.
2. Siphon old fluid from the master-cylinder reservoir and refill with fresh DOT 4.
3. Fit the pressure bleeder, set 2.0 bar, and check for leaks at the cap.
4. Clean every bleed nipple before opening it. Brake fluid strips paint.

Wheel / nipple order

Mercedes numbers the corners 1–2–3–4 and says that order must be followed. In practice that is the longest circuit first:

1. Rear right
2. Rear left
3. Front right
4. Front left

Front fixed calipers on many W463s have two or three bleed screws. Bleed each caliper in this order:

1. Inner bleed screw, bottom (A)
2. Outer bleed screw, bottom (B)
3. Outer bleed screw, top (C)

If your fronts only have two nipples, use the inner-top then remaining outer nipple as marked on that caliper. Rear floating calipers normally have one nipple.

Bleed each corner

1. Cap off, hose on, other end in a bottle with a little fresh fluid.
2. Open the nipple.
3. Let fluid run until it is clean and bubble-free (about 80 cm³).
4. Close the nipple before you move the hose.
5. Repeat on every nipple on that caliper, then the next wheel.
6. Never open more than one nipple at a time.

Two-person pedal bleed works for a simple fluid change if you cannot pressure-bleed: helper presses and holds, you open, close before they release, then they lift the pedal slowly. Do not pump the pedal in jerks.

ABS hydraulic unit

A normal flush often does not empty the ABS block. After bleeding the four wheels:

• Pump the pedal several times until it is firm.
• If it is still soft, or you opened the ABS unit / lines at the modulator, use a scanner:
  • Ignition ON, engine OFF
  • Chassis → ABS / ESP / traction systems
  • Maintenance / special functions → bleed / activate high-pressure and return pump
    Follow the on-screen prompts and keep the reservoir full. Then re-bleed the wheels if the tool tells you to.

A dealer STAR/Xentry session is the surest way after an ABS unit change.

Finish

1. Release bleeder pressure, remove the adapter, set the reservoir to MAX.
2. Refit dust caps.
3. Pump the pedal until the pads sit on the discs and the pedal is hard.
4. Check for leaks at nipples, hoses and the master cylinder.
5. Short low-speed test in a safe place. Confirm ABS warning lamp is out after a short drive.

If the pedal is spongy after all of that, there is still air in the modulator or a leak — do not drive it as normal until it is firm.