BMW 135is Brake Master Cylinder Replacement at your home or office.

How do mechanics replace the brake master cylinder?

• On vehicles with power brakes, the master cylinder is bolted to the metal housing of the power brake booster. There is usually an electrical plug connecting to a brake fluid level sensor on the master cylinder reservoir and that plug must be disconnected.
  
• Once all steel brake lines are disconnected from the master cylinder, the master cylinder is unbolted from the brake booster and removed from the vehicle.
• The new master cylinder must be bench-bled to expel air from internal passages that contain the piston. Then the new master cylinder is bolted to the brake booster and the brake lines are reattached. The electrical plug for the fluid level sensor is reconnected.
• Whenever a new master cylinder is installed, brakes lines to wheel positions must be bled to remove air, old fluid and contaminants. If your vehicle is equipped with anti-lock brakes, the mechanic may use a bidirectional scan tool during brake bleeding to actuate the ABS pump, thus ensuring that all air is removed from the complex valving in the ABS system.
• All brake line connections that were removed during the master cylinder replacement are inspected for any leakage and the vehicle is road tested to ensure normal operation of the brakes.