Dorman M390279 Brake Master Cylinder

Reliable Brake Master Cylinder for Chevrolet and GMC Trucks

The Dorman M390279 brake master cylinder is designed to restore proper brake function in Chevrolet and GMC heavy-duty trucks. Engineered with a 1.25-inch bore diameter and constructed from durable aluminum, this master cylinder includes a reservoir to ensure consistent brake fluid supply.

• Master cylinder bore diameter: 1.25 inches for precise hydraulic pressure
• Durable aluminum construction for corrosion resistance
• Includes reservoir for brake fluid storage
• Two outlet ports with rearward outlet size 1/2-20 and secondary outlet thread diameter 9/16-18
• Compatible with Chevrolet C3500, K3500, P30, and P3500 models
• Mounting hardware not included

Product Details and Specifications

The Dorman M390279 brake master cylinder is built to meet the hydraulic braking needs of heavy-duty Chevrolet and GMC trucks such as the C3500, K3500, P30, and P3500. Its aluminum body offers strength and resistance to corrosion, which is critical for long-term brake system reliability. The 1.25-inch bore diameter ensures proper hydraulic pressure is maintained for effective braking performance. This master cylinder features two outlets: a rearward outlet sized at 1/2-20 and a secondary outlet with a 9/16-18 thread diameter, allowing for secure brake line connections. The included reservoir provides a reliable source of brake fluid, though mounting hardware is not part of the package.

Common Applications and Problem Resolution

• Restores brake pressure in Chevrolet C3500 and GMC K3500 trucks
• Replaces worn or leaking master cylinders in P30 and P3500 models
• Addresses brake fluid reservoir leaks or damage
• Solves inconsistent brake pedal feel or sponginess
• Fixes brake system hydraulic failures due to master cylinder wear

Installation Notes and Tips

When installing the Dorman M390279 brake master cylinder, ensure the brake system is properly bled to remove air and maintain hydraulic integrity. Since mounting hardware is not included, reuse existing hardware or acquire compatible fasteners. Verify outlet thread sizes (1/2-20 rearward and 9/16-18 secondary) to ensure proper brake line fitting. Inspect brake lines and connections for leaks after installation.

Quality Assurance and Warranty Information

Dorman manufactures the M390279 brake master cylinder to meet or exceed OEM specifications for Chevrolet and GMC heavy-duty trucks. The aluminum construction and included reservoir contribute to long-lasting performance. While mounting hardware is not included, the part is backed by Dorman's quality standards. Please refer to Dorman's warranty policy for specific coverage details.