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:

• Multiple aircraft experienced brake system malfunctions, primarily related to the master cylinder, resulting in partial or complete loss of braking.
• Common master cylinder issues included internal failures such as stuck bypasses, torn O-rings, fluid contamination, and unthreaded components leading to pressure loss.
• Other brake failures stemmed from installation problems or inadequate component strength, such as a piston rod shearing due to improper clearance or a critical cotter pin shearing.

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