how to fix the brake pedal sinking to the floor on my BMW 3 Series

Solution

1. Preparation

• Gather necessary tools and parts.
• Park the vehicle on a flat surface and engage the parking brake.
• Disconnect the battery to ensure safety.

2. Inspect and Replace Brake Fluid

• Sub-steps:
  • Remove the brake fluid reservoir cap.
  • Use a turkey baster or siphon to remove old brake fluid.
  • Refill with new brake fluid (DOT 4 recommended for most BMW models).
• Tools Required: Turkey baster, brake fluid, funnel.
• Safety Warnings: Brake fluid is corrosive; avoid contact with paint and skin.

3. Check and Replace Brake Lines

• Sub-steps:
  • Inspect all visible brake lines for corrosion or damage.
  • If damaged, use a line cutter to remove the defective section.
  • Replace with new brake lines and secure with appropriate fittings.
  • Bleed the brake system to remove air from the lines.
• Tools Required: Line cutter, wrench set, brake line fittings.
• Safety Warnings: Ensure no pressure is left in the brake system before working on lines.

4. Inspect and Replace Master Cylinder

• Sub-steps:
  • Locate the master cylinder (typically near the driver's side).
  • Disconnect the brake lines from the master cylinder using the appropriate wrench.
  • Remove the master cylinder mounting bolts and carefully detach it.
  • Install the new master cylinder, torque bolts to manufacturer specifications (consult service manual).
• Tools Required: Wrench set, socket set, torque wrench.
• Safety Warnings: Handle hydraulic components with care to avoid fluid exposure.

5. Inspect and Replace Brake Pads and Rotors (if necessary)

• Sub-steps:
  • Remove the wheel using a lug wrench.
  • Inspect brake pads for thickness; replace if below manufacturer specifications.
  • Check rotors for scoring or warping; replace as needed.
  • Install new pads and rotors, ensuring proper alignment.
• Tools Required: Lug wrench, socket set, brake pad spreader.
• Safety Warnings: Use jack stands for safety when lifting the vehicle.