Dorman M390178 Brake Master Cylinder

Reliable Brake Master Cylinder for Chevrolet, Oldsmobile, and Pontiac

The Dorman M390178 brake master cylinder is engineered to restore proper brake hydraulics in select GM minivans. Designed specifically for Chevrolet Lumina APV, Oldsmobile Silhouette, and Pontiac Trans Sport models, this master cylinder ensures consistent brake fluid pressure and reliable stopping power.

• Master cylinder bore diameter: 24 mm for precise hydraulic control
• Constructed from durable aluminum material for corrosion resistance
• Includes reservoir for brake fluid storage and monitoring
• Equipped with a sensor to support brake system diagnostics
• Two outlets with secondary outlet thread diameter of 10 mm (M10 x 1.0 thread pitch)
• Rearward outlet size: M10 x 1.0 for secure brake line connections
• Package contains the master cylinder unit only; mounting hardware not included

Detailed Product Description

The Dorman M390178 brake master cylinder is a direct replacement part designed to meet the specifications of original equipment for Chevrolet Lumina APV, Oldsmobile Silhouette, and Pontiac Trans Sport vehicles. Its 24 mm bore diameter allows for accurate brake fluid displacement, ensuring consistent pedal feel and braking performance. The aluminum construction offers enhanced durability and resistance to corrosion, extending the service life of the component. This master cylinder comes with an integrated reservoir and sensor, facilitating fluid level monitoring and brake system diagnostics. The two outlet ports, including a rearward outlet sized M10 x 1.0, provide secure connections to the brake lines, maintaining system integrity.

Common Brake Issues Addressed

• Brake pedal sinking or sponginess due to master cylinder wear
• Brake fluid leaks from the master cylinder reservoir or outlets
• Inconsistent brake pressure affecting stopping performance
• Faulty brake fluid level sensor triggering warning lights
• Corrosion-related master cylinder failure in older vehicles

Installation Notes and Tips

• Ensure compatibility with Chevrolet Lumina APV, Oldsmobile Silhouette, or Pontiac Trans Sport before installation
• Bleed the brake system thoroughly after installation to remove air
• Use appropriate brake fluid as specified by the vehicle manufacturer
• Mounting hardware is not included; retain original hardware or source separately
• Inspect brake lines and fittings for wear or damage during replacement

Quality Assurance and Warranty

Dorman manufactures the M390178 brake master cylinder to meet or exceed OEM standards for fit, form, and function. The aluminum construction and integrated sensor contribute to reliable operation within the brake hydraulic system. While specific warranty details may vary, Dorman typically offers a limited warranty covering defects in materials and workmanship. Refer to the product documentation for exact warranty terms.