Brake Servo Unit Mercedes Vito W639 Brake Booster Master Cylinder A6394300208

Brake Servo Unit Mercedes Vito W639 Brake Booster Master Cylinder is a braking system component from the Brake servos and pressure regulators group, designed for Mercedes Vito and Viano W639 series vehicles. It is responsible for assisting the pressure applied to the brake pedal, which translates into stable, predictable, and comfortable deceleration during daily operation.

Specifications and technical data

• SKU: rhd-A6394300208
• Mark: Mercedes (Genuine OE)
• Condition: Used
• OEM Part Number: A6394300208
• Substitutable numbers: A6394300208, A 639 430 02 08, A0004311727, A 000 431 17 27, A6394300102, A 639 430 01 02, A0004316901, A 000 431 69 01, BG
• Category: Brake Servos

Purpose and function in the braking system

The brake servo in Vito and Viano W639 models acts as an amplifier for the force generated by the driver on the brake pedal. Thanks to vacuum assistance, the system requires less foot pressure, and the vehicle's response to braking is smoother and more repeatable. A properly selected servo allows for maintaining stable pressure in the brake circuit, which is particularly important in commercial and family vehicles that are often operated under heavier loads.

Application and compatibility

The offered component comes from the Mercedes vehicle line and is structurally matched to the braking system architecture of the W639 platform. The servo works with the factory brake master cylinder and other system components, maintaining the operating parameters specified by the manufacturer. The presence of dedicated part numbers and interchangeable numbers allows for precise verification of compatibility with a specific engine version and model year of the vehicle without the need for installation modifications.

Technical and operational characteristics

The brake servo from this series has been designed for intensive, long-term operation in both urban and extra-urban conditions. The construction based on a vacuum diaphragm ensures:

• stable assistance across the full range of brake pedal travel,
• repeatable braking force characteristics under various vehicle loads,
• consistent cooperation with safety systems (ABS, ESP) present in the W639 platform.

By maintaining factory geometry and mounting points, the servo integrates with the firewall and pedal assembly without the need for interference with the body structure. This solution reduces installation time and minimizes the risk of leaks in the engine compartment area.

Condition, origin, and benefits of choosing a used part

The offered component comes from the used parts segment, which allows for combining rational repair costs with maintaining the manufacturer's original specifications. Choosing an OEM servo from dismantling is a beneficial solution wherever the priority is to maintain factory braking characteristics and compatibility with the existing hydraulic and electronic installation. This type of component is particularly attractive for maintenance repairs when you want to reduce costs without sacrificing the predictable operation of the system.

Installation tips and part selection

When replacing the brake servo in a Mercedes Vito or Viano W639, it is recommended to:

• verify compatibility by part number and interchangeable numbers,
• check the condition of the brake master cylinder and rigid lines in the installation zone,
• check the vacuum system for leaks after completing the work.

Selecting the correct servo from the Brake servos and pressure regulators group allows you to maintain the factory feel of the brake pedal and avoid unwanted changes in the system's operating characteristics.

If you are planning a comprehensive repair or upgrade of the braking zone in your Mercedes and need other elements from the same group, such as servos, pressure regulators, or additional assistance components, check the available parts in the Mercedes brake servos and pressure regulators category.

For a complete approach to vehicle service, also covering the thermal comfort of the driver and passengers, it is worth checking out practical tips on selecting and maintaining components responsible for cabin temperature – you will find them in the article Air conditioning and heating – part selection and maintenance for year-round comfort.