MPA Electrical NM55686 Brake Master Cylinder

Brake Master Cylinder for BMW X3 and X4

Restore consistent brake pedal response with this MPA Electrical brake master cylinder, part number NM55686. It is a standard replacement unit for BMW X3 and BMW X4 models with front disc brakes, built with an aluminum body and a 1.039-inch bore for OE-style hydraulic performance.

MPA Electrical’s New with front disc brakes product line focuses on direct-fit brake hydraulic replacements for vehicles that use front disc brake configurations. NM55686 is tested against OE specifications using controlled inspection processes to help deliver reliable braking performance after installation.

• Fits 2015-2018 BMW X4, N/A, new with front disc brakes
• Fits 2011-2017 BMW X3, N/A, new with front disc brakes
• Standard replacement brake master cylinder
• Aluminum master cylinder construction
• 1.039-inch bore diameter
• Gasket or seal included
• Uses DOT 4 brake fluid
• Two mounting holes with 0.357-inch mounting hole diameter
• No reservoir, cap, booster, push rod, sensor, or mounting hardware included

This part cross-references BMW OE numbers 34 3 6 857 872 and 34 33 6 797 471 for the same application.

Detailed Product Overview

NM55686 is a brake master cylinder for BMW X3 and BMW X4 applications that require a front disc brake setup. The aluminum housing helps keep the unit lightweight while maintaining the hydraulic integrity needed for dependable brake pedal feel. With a 1.039-inch bore and DOT 4 fluid compatibility, this master cylinder is built to match the braking system requirements of the listed vehicles.

Use this BMW X3 brake master cylinder or BMW X4 brake master cylinder when replacing a worn, leaking, or internally bypassing unit. The included gasket or seal supports a proper hydraulic seal during installation, while the standard replacement design helps maintain OE-style fitment and function.

Common Issues This Part Can Address

• Soft or sinking brake pedal
• Brake fluid leakage at the master cylinder
• Internal hydraulic bypass causing reduced braking response
• Uneven or inconsistent pedal pressure
• Brake warning symptoms related to master cylinder wear

Installation Notes and Tips

Before installation, confirm the vehicle is equipped with front disc brakes and verify the master cylinder bore and mounting dimensions match the original unit. Bench bleeding is recommended before connecting brake lines to reduce trapped air in the hydraulic system. Because the reservoir, cap, booster, push rod, sensor, and mounting hardware are not included, reuse or source those components as needed for the specific vehicle setup.

Quality Assurance

MPA Electrical tests each brake master cylinder against OE specifications using proprietary inspection processes and strict protocols. That approach helps ensure consistent hydraulic performance and dependable operation right out of the box for BMW X3 and BMW X4 brake system service.