ACDelco 18M221B Professional Brake Master Cylinder Assembly with Reservoir

The ACDelco 18M221B is a Professional-grade brake master cylinder assembly engineered to deliver reliable hydraulic braking performance. Built with both cast iron and aluminum castings, this master cylinder provides a durable, high-quality replacement that fits precisely without placing extra stress on the brake booster mounting.

Key Features:

• SAE J1153 & J1154 compliant — meets industry brake performance testing requirements for reliability and quality
• Pressure tested prior to shipping to ensure safe, confident braking performance
• Cast iron and aluminum construction — no extra stress on brake booster mounting interface
• EPDM and SBR rubber internal components — superior resistance to heat, corrosion, and fluid leakage
• Precision geometrical tolerances ensure the body and plastic reservoir mate correctly for a leak-free fit
• Piston assembly and return spring help prevent brake drag that can accelerate brake pad wear
• Includes reservoir, cap, bleeder hoses, and pushrod — ready to bench bleed and install, no assembly required
• 0.937" (23.8 mm) bore diameter with dual-port outlet configuration
• OEM Cross-Reference: 19176455 | Replaces OE part numbers including 12385316, 15679677, 15659911, 22586989, and others

This ACDelco Professional brake master cylinder is a direct-fit replacement unit that ships ready for bench bleeding and installation straight out of the box. It is manufactured to meet stringent OEM fit, form, and function standards, making it a trusted choice for restoring proper hydraulic brake system operation.