BMW 1 3 Series E81 E90 E91 E92 LCI Brake Servo Unit Master Cylinder 6788040

BMW 1 3 Series E81 E90 E91 E92 LCI Brake Servo Unit Master Cylinder is an original brake servo unit with a master cylinder, designed for the factory BMW braking system. As a component from the Brake Servos and Proportioning Valves group, it ensures stable conversion of pedal force into system pressure, which translates into predictable, safe braking in daily operation. This is an OEM solution that allows you to maintain the braking system's performance characteristics in accordance with the manufacturer's specifications.

Specifications and technical data

• SKU: rhd-6788040
• Mark: BMW (Genuine OE)
• Condition: Used
• OEM Part Number: 6788040
• Substitutable numbers: 6788040, 34336779721, 6779721, 34336785665, 6785665, 34326764117, 6764117, 34316764132, 6764132, 34336779722, 6779722, 34336764130, 6764130
• Category: Brake Servos

Purpose and compatibility

The presented brake servo unit with master cylinder is dedicated to BMW 1 and 3 Series models of the E81, E90, E91, and E92 generations after the facelift (LCI). The design was developed specifically for the body geometry and braking system of these versions, ensuring the correct pedal position, operating travel, and assistance characteristics are maintained.

Its original BMW origin means that the component is designed to work with factory brake lines, the ABS/DSC pump, and other system components without the need for modifications or adaptations.

Construction and function of the brake servo unit with master cylinder

The brake servo is responsible for increasing the force exerted by the driver on the pedal by utilizing vacuum from the engine system. Combined with the master cylinder, it forms a complete unit responsible for generating operating pressure in the brake circuits.

• stable conversion of pedal force into pressure in the brake lines,
• maintenance of the factory pedal "feel" and firmness,
• proper cooperation with safety systems (ABS/DSC),
• appropriate distribution of pressure between the front and rear axle circuits.

As a result, the driver receives a predictable vehicle response to brake pedal input, which is crucial both in city driving and during dynamic use.

Benefits of using an original BMW unit

Using an original brake servo unit with master cylinder in a BMW 1 or 3 Series allows for maintaining the consistency of the entire braking system. Factory fitment minimizes the risk of leaks, incorrect pedal travel, or uneven brake performance between axles.

Key advantages include:

• secure fitment with the bulkhead and brake pedal,
• retention of original mounting points and connections,
• no need for adapters or installation modifications,
• consistency with factory BMW service procedures.

For users who value handling precision and predictable vehicle behavior, the original BMW brake servo unit is a solution that allows you to maintain braking parameters at the level intended by the manufacturer.

Condition, verification, and service application

The component comes from the secondary market, which allows for economical repair of the braking system while maintaining an OEM component. This type of unit is particularly useful for:

• repairs following a servo or master cylinder failure (loss of assistance, "soft" pedal),
• comprehensive renovation of the braking system in a BMW E81/E90/E91/E92 LCI,
• restoring a vehicle to factory specifications after previous modifications.

Before installation, it is recommended to perform a standard brake system leak test, bleed the system according to BMW procedures, and verify the correct operation of the pedal throughout its full range of travel.

Technical support, selection, and related content

For precise part selection, it is worth using OEM markings and interchangeable numbers assigned to a specific BMW configuration – this helps avoid compatibility issues and speeds up the service process. In case of doubt, selection by Vehicle Identification Number (VIN) is the recommended verification method.

If you are planning a comprehensive repair or upgrade of the braking zone in your BMW and need other elements from the same group, such as servos, proportioning valves, or complete assistance units, check out the available parts in the BMW Brake Servos and Proportioning Valves category.

To better understand the relationships between comfort and safety systems in a car and the importance of proper OEM component selection, it is worth reading the guide on our blog: Air conditioning and heating – part selection and maintenance for year-round comfort.

Additional information on the benefits of using original, used components in cars of the Bavarian brand is provided in the article: BMW – sports performance and precision. How do original used parts extend the life of a Bavarian icon?, which discusses practical aspects of selecting parts by OEM numbers and the impact of such solutions on the durability and handling characteristics of a BMW.