Replace a leaking or worn master cylinder with the Dorman First Stop Brake Master Cylinder M390186, a new unit that converts brake pedal effort into hydraulic pressure for the brake lines. It fits many vehicles, among them the 1995-1999 Buick Riviera, 1995-1999 Oldsmobile Aurora and 1991-1995 Buick LeSabre (all engines). See the "Vehicles it fits" section for the full list. Dorman precision-engineered it to replicate the design, function and performance of the original master cylinder on the listed applications, and built it from new, high-quality materials for a safe, durable replacement.
- Precise replacement: the aluminum cylinder housing is built to match the original part's material for 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, with quality and safety in mind.
- Strict specifications: made to meet rigorous SAE International standards.
Specifications: 1 in. bore diameter and 2 outlets. The rearward outlet size is M10 x 1.0, the secondary outlet thread diameter is M12 x 1.0, and the primary outlet thread pitch is 1 mm. The unit ships as one master cylinder with the reservoir and sensor included. Mounting hardware is not included. Country of origin: China.
Signs that a master cylinder may need replacing include a soft or sinking brake pedal, brake fluid leaking at the cylinder or reservoir, and a fluid level that keeps dropping. Other brake components can cause similar symptoms, so diagnose the cause before replacing. If the master cylinder is at fault, M390186 replaces it.
Frequently Asked Questions
Is this the right Buick LeSabre master cylinder for a 1991-1995 model?
It is listed as a direct-fit replacement for the 1991-1995 Buick LeSabre with all engines. Check the "Vehicles it fits" section to confirm your exact vehicle.
Does it fit the 1995-1999 Buick Riviera and 1995-1999 Oldsmobile Aurora?
Yes. The listed applications include the 1995-1999 Buick Riviera and the 1995-1999 Oldsmobile Aurora. The "Vehicles it fits" section shows the complete fitment.
Does it come with a reservoir and sensor?
Yes, the reservoir and sensor are both included. Mounting hardware is not, so consult the vehicle service information for the correct fasteners and whether they may be reused.
What are the bore and outlet specifications?
It has a 1 in. bore and 2 outlets. The rearward outlet is M10 x 1.0, the secondary outlet thread diameter is M12 x 1.0, and the primary outlet thread pitch is 1 mm.
What should I know before installing it?
Master cylinders are typically bench-bled before installation, and the brake system is bled afterward. Follow the vehicle service information and use the brake fluid your vehicle's manufacturer specifies.
