Brake Booster BMW F46 Servo Brake Master Cylinder Expansion Tank 6857914

Brake Booster BMW F46 Servo Brake Master Cylinder Expansion Tank is a complete, original solution from the BMW group, designed for the factory braking system of the 2 Series Gran Tourer F46 models. The set combines a brake servo, master cylinder, and fluid reservoir in one unit, which facilitates installation and ensures consistent operation of the entire system. It is a practical choice for users looking for a compatible OEM component for professional brake system repair.

Specifications and technical data

• SKU: 6857914
• Mark: BMW (Genuine OE)
• Condition: Used
• OEM Part Number: 6873430
• Substitutable numbers: 6873430, 34336873430, 6868997, 34336868997, 6866164, 34336866164, 6857914
• Category: Brake Servos

Purpose and function in the BMW braking system

The presented brake servo assembly with master cylinder and reservoir has been designed specifically for the geometry and parameters of the BMW F46 braking system. The servo is responsible for increasing the force applied to the brake pedal, the master cylinder converts it into pressure in the hydraulic circuits, and the reservoir ensures the correct level of operating fluid. Thanks to this, the driver receives stable, predictable brake performance while maintaining the factory feel of the pedal.

Set construction: servo, master cylinder, and reservoir

The element belongs to the Brake Servos and Proportioning Valves group, which means it is responsible not only for assistance but also for the correct distribution of braking force between the vehicle's axles. Integrating the servo with the master cylinder and expansion tank reduces the number of connections, facilitates installation, and minimizes the risk of leaks in the system. The OEM solution ensures proper fitment to the bulkhead mounts, the brake pedal, and the factory brake lines.

Selection by OEM number and interchangeable numbers

As an original BMW component, the part has a dedicated OEM number and associated interchangeable numbers, which facilitates precise identification in the manufacturer's catalogs and service systems. When selecting for a specific F46 unit, it is worth comparing the part number with the vehicle documentation or the removed element to maintain full specification compliance. If in doubt, the guide on selecting car parts by VIN and OEM number will be helpful – you can find it in the article Guide: how to choose the right car part by VIN and OEM number, where the verification process is described step by step.

Condition, installation advantages, and service application

The offered element is a used OEM BMW component, which in practice means factory fitment to the braking system and preservation of the original operating characteristics. Compared to replacements, using a part from the same production line allows for reducing the risk of compatibility issues, such as incorrect pedal travel, different mounting points, or differences in the master cylinder piston diameter. The servo–master cylinder–reservoir set is particularly useful for:

• repairs after brake booster failure,
• mechanical damage to the master cylinder,
• leaks around the brake fluid reservoir,
• comprehensive regeneration of the brake system in the BMW F46.

Integration with other components of the BMW braking system

Replacing the servo assembly with the master cylinder and reservoir should be treated as part of a broader brake system service – especially in vehicles operated intensively or with high mileage. After installation, it is recommended to thoroughly bleed the system, check the flexible and rigid lines, and verify the condition of the discs and pads. If you are planning a comprehensive repair or upgrade of the braking system in your BMW and need other elements from the same group, such as servos, proportioning valves, or complete booster modules, check the available parts in the BMW Brake Servos and Proportioning Valves category.

Technical support and operation

With any intervention in the braking system, it is worth paying attention to the general technical condition of the vehicle, including cooperating safety and comfort systems. For a fuller picture of car maintenance, including the selection of used OEM components and service planning, the blog article Air conditioning and heating – part selection and maintenance for year-round comfort will be helpful, where practical service procedures and principles of working with original components are discussed.

Summary

Brake Booster BMW F46 Servo Brake Master Cylinder Expansion Tank is a functional, original element from the BMW group, intended for professional brake system repair. The integrated design, factory fitment, and the presence of interchangeable numbers facilitate selection and installation, and the use of an OEM component allows for maintaining predictable, safe braking characteristics in your BMW F46.