Raybestos MC390850 Brake Master Cylinder

Brake Master Cylinder Overview

Raybestos MC390850 is a brake master cylinder for select medium-duty applications that require a 40 mm bore and aluminum construction. It is part of the Raybestos Element3; New line and is built around the port and mounting specifications needed for direct hydraulic replacement.

Compatible With Workhorse W42, Workhorse W18, Workhorse W16, Chevrolet C4500 Kodiak, and GMC C4500 Topkick applications listed below. The MC390850 part number is also useful when cross-checking replacement options for the same brake hydraulic setup.

Key Features

• Aluminum master cylinder body for a lighter, corrosion-resistant design.
• 40.000 bore size for the specified hydraulic application.
• Two mounting holes with 0.433 diameter for the listed fitments.
• Primary and secondary port threads: 9/16"-18 and 1/2"-20.
• Raybestos Element3; New product line for brake hydraulic replacement.

Detailed Description

Raybestos MC390850 is engineered for vehicles that use the specified Delco master cylinder and rectangular reservoir configuration shown in the fitment data. The aluminum housing, 40 mm bore, and port thread sizes make it a precise match for the brake hydraulic requirements on select Workhorse Custom Chassis W42 and Workhorse W18 applications, as well as Chevrolet C4500 Kodiak and GMC C4500 Topkick models with the listed notes. The MC390850 part number should be matched carefully to the original hydraulic layout before installation.

This part cross-references Cardone New 13-3798 for the same application.

What It Is Used For

• Restoring brake pedal pressure when the master cylinder is worn internally.
• Addressing fluid bypass that can reduce hydraulic performance.
• Replacing a leaking master cylinder body or seal area.
• Correcting brake response issues tied to bore or port mismatch.
• Servicing brake hydraulic systems on the listed medium-duty platforms.

Installation Notes and Tips

Verify the original master cylinder bore, port thread sizes, and reservoir style before ordering. Confirm the vehicle notes in the fitment table, including Delco master cylinder and axle-related exceptions where listed. Bleed the brake system thoroughly after installation and inspect all hydraulic connections for leaks.

Quality Assurance

Raybestos Element3; New is positioned as a brake replacement line for hydraulic service parts. Match the MC390850 to the original application details to ensure the correct fitment and brake system configuration.