Raybestos MC39027 Brake Master Cylinder

Brake Master Cylinder for GM Compact Cars

The Raybestos Element3 New MC39027 is a brake master cylinder built for select Buick, Chevrolet, Oldsmobile, and Pontiac applications from the late 1970s and 1980. It features an iron body, a 0.875 bore size, and a two-port layout for direct hydraulic connection in the brake system.

Use this Raybestos brake master cylinder when servicing a vehicle that needs a replacement hydraulic unit with the correct mounting and port configuration. The MC39027 is listed for Buick Skyhawk, Chevrolet Monza, Oldsmobile Starfire, and Pontiac Sunbird applications.

Key Features

• Iron master cylinder construction for brake hydraulic service
• 0.875 bore size
• 2 mounting holes with 0.423 mounting hole diameter
• 2 ports for brake line connection
• Primary port thread: 1/2"-20
• Secondary port thread: 9/16"-18
• Raybestos Element3 New product line

Fitment Details

• Fits 1976-1980 Buick Skyhawk, N/A
• Fits 1978-1980 Chevrolet Monza, N/A
• Fits 1978-1980 Oldsmobile Starfire, N/A
• Fits 1978-1980 Pontiac Sunbird, N/A
• Fits 1976-1977 Chevrolet Monza, N/A with Cast Iron Cylinder; with Stamped Steel Cylinder; Element3; New
• Fits 1976-1977 Oldsmobile Starfire, N/A with Cast Iron Cylinder; with Stamped Steel Cylinder; Element3; New
• Fits 1976-1977 Pontiac Sunbird, N/A with Cast Iron Cylinder; with Stamped Steel Cylinder; Element3; New

Detailed Description

Raybestos MC39027 is a brake master cylinder engineered for select GM compact platforms, including Buick Skyhawk, Chevrolet Monza, Oldsmobile Starfire, and Pontiac Sunbird. The iron housing and 0.875 bore size support hydraulic brake system replacement where the original master cylinder uses a two-port design and the specified thread sizes.

This part cross-references Bosch 18087 for the same application. The Raybestos Element3 New line identifies this as a new replacement part within the Element3 family, making it a direct-fit option for vehicles that match the listed mounting and port specifications.

Common Replacement Reasons

• Brake pedal travel that increases due to internal master cylinder wear
• Loss of hydraulic pressure in the brake system
• Brake fluid leakage at the master cylinder body or ports
• Corrosion or damage to the original iron master cylinder
• Need for the correct bore, port, and mounting configuration during brake repair

Installation Notes and Tips

Verify the bore size, mounting hole count, and port thread sizes before installation. Confirm the vehicle’s original master cylinder style, especially on 1976-1977 Chevrolet Monza, Oldsmobile Starfire, and Pontiac Sunbird applications that list cast iron cylinder and stamped steel cylinder configurations. Always inspect brake lines, fittings, and the rest of the hydraulic system during replacement.

Quality Assurance

Raybestos is a recognized brake parts brand, and the Element3 New line provides a replacement master cylinder built to match the listed application requirements. Confirm fitment by part number MC39027 and the vehicle-specific details before installation.