Brake Master Cylinders

After a brake master cylinder was installed, the technician was unable to bleed the brake system. Fluid pulled from reservoir would return to reservoir through the same line as the internal bypass was not functioning properly. Master cylinder was disassembled and bypass was found stuck and unable to move. Metal shavings were found inside, and an O-ring was torn, with black specks mixed in with the shavings. Part replaced with new master cylinder.

Key Takeaways:

• Aircraft brake system failures frequently stem from issues with the master cylinder, affecting various aircraft types.
• Common master cylinder malfunctions include internal component defects (e.g., stuck bypass, torn O-rings, metal shavings), improper assembly (e.g., bottomed-out clevis, unthreaded gland), and general wear or contamination.
• These failures consistently lead to a partial or complete loss of braking capability, often requiring replacement or overhaul of the master cylinder.
• Incidents underscore the critical importance of meticulous maintenance, correct installation procedures, and robust component design for reliable brake system operation.

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