BMW 1 3 Series E81 E87 E90 E91 E92 Brake Servo Unit Master Cylinder 6785645

BMW 1 / 3 Series E81 E87 E90 E91 E92 Brake Booster integrated with the master cylinder is an original BMW braking system component, designed for precise cooperation with the vehicle's factory hydraulics. As part of the Brake Boosters and Force Correctors group, it is responsible for the stable transfer of pedal pressure to pressure in the brake circuits, which translates to predictable vehicle behavior during braking. This solution is dedicated to models of the 1 and 3 Series, E8x/E9x generation, allowing for the preservation of the system's factory operating parameters.

Specifications and technical data

• SKU: rhd-6785645
• Mark: BMW (Genuine OE)
• Condition: Used
• OEM Part Number: 6785645
• Substitutable numbers: 6785645, 34336779718, 6779718, 34336764122, 6764122, 34336785663, 6785663, 34336779719, 6779719, 34316764124, 6764124, 34326764117, 6764117, AS, 13537568050, 7568050, 13537528350, 7528350
• Category: Brake Servos

Purpose and Function in the Braking System

The presented brake booster integrated with the master cylinder is a key component of the hydraulic braking system in BMW 1 and 3 Series, E generation. It is responsible for:

• assisting the brake pedal pressure using vacuum from the engine or a vacuum pump,
• precise metering of pressure in the brake circuits through the master cylinder,
• maintaining a stable pedal engagement point, which improves brake feel,
• cooperating with safety systems such as ABS or stability control by providing adequate working pressure.

Thanks to its factory BMW design, this component is optimized for pedal geometry, piston stroke, and boost characteristics, ensuring consistency with the vehicle's original configuration.

Original BMW Part – Fitment and Compatibility

This is an original BMW component, meaning full compliance with the manufacturer's factory standards regarding materials, manufacturing tolerances, and operating parameters. Using OEM parts instead of aftermarket alternatives allows for:

• maintaining the brake pedal's operating characteristics as intended by the manufacturer,
• minimizing the risk of compatibility issues with the vehicle's electronics,
• ensuring correct mounting to the bulkhead and proper connection of brake lines.

Additionally, the part has assigned replacement numbers, which facilitates selecting the correct variant for a specific vehicle configuration – especially when working with parts catalogs or selecting by OEM numbers.

Performance Characteristics and Installation Advantages

The brake booster with master cylinder in this configuration is prepared for installation as a complete unit, simplifying service work compared to replacing individual sub-assemblies. The main advantages of this solution include:

• maintaining the factory rigidity of the pedal–booster–master cylinder system,
• reducing the risk of leaks due to the use of original connections,
• consistency of operating parameters with the stock braking system of BMW 1 and 3 Series E8x/E9x.

The complete brake booster unit allows for restoring the correct operation of the system in case of wear or damage to the existing component, without the need for installation modifications.

Part Condition and Application in Service Practice

The offered component comes from the secondary market and is intended for service applications in BMW vehicles where restoring the factory braking system's efficiency is required while maintaining a favorable cost-to-quality ratio. In workshop practice, such a component is particularly useful in:

• post-accident repairs where the bulkhead or booster mounting has been damaged,
• cases of brake boost loss or unstable pedal operation,
• comprehensive restorations of 1 and 3 Series, E generation vehicles, where preserving original BMW solutions is a priority.

Choosing a used OEM part allows for maintaining high quality of the braking system while simultaneously reducing costs compared to purchasing a new component.

Safe Online Selection of Used Parts

When selecting a used brake booster with master cylinder, it is crucial to verify compatibility by OEM number and reference numbers, as well as to match it to the specific body version and engine. It is advisable to use selection procedures based on catalog numbers and manufacturer documentation to avoid installation problems. For users who want to streamline the purchasing process, we have prepared a practical guide: how to safely buy used car parts online step by step, which describes, among other things, selection by OEM numbers and cooperation with workshops.