Turn pedal effort into hydraulic brake pressure with the Dorman First Stop Brake Master Cylinder M39309, a new cast iron unit with two outlets and the reservoir included. It fits many vehicles, among them the 1976-1996 Chevrolet G30, 1977-1996 Chevrolet P30 and 1979-1996 GMC G3500, all engines. See the Buyer's Guide tab for the full list.
Dorman precision-engineers this master cylinder to match the design, function and performance of the original unit on the listed applications. It is built from new, high-quality materials for a safe, durable replacement.
- Precise replacement: The cylinder housing is made to match the casting material of the original part and is intended to deliver similar performance.
- Durable design: Every rubber component uses a high-quality EPDM compound that resists glycol-based brake fluid.
- 100% new: Made entirely of new materials for quality and safety.
- Strict specifications: Built to meet rigorous SAE International standards.
Specifications: 34 mm bore diameter; two outlets; 1/2-20 in. secondary outlet thread; reservoir included; sensor not included; mounting hardware not included. Country of origin: China.
A master cylinder may need replacing if the brake pedal feels spongy or slowly sinks under steady pressure, or if brake fluid leaks from the cylinder or reservoir. Other brake components can cause similar symptoms, so diagnose the cause before replacing. Consult the vehicle service information for the correct fasteners and whether they may be reused, and bleed the brake system according to the service procedure after installation.
