Generate the hydraulic pressure your brakes depend on with the Dorman - First Stop Brake Master Cylinder M390186. Pressing the brake pedal pushes fluid from this cylinder to the wheel circuits, and this unit is engineered to match the original's design and function on the listed GM applications — including the 1991-1995 Buick LeSabre and Park Avenue, 1995-1999 Buick Riviera, 1991-1993 Cadillac DeVille, 1991-1995 Oldsmobile 98, and 1991-1995 Pontiac Bonneville. See the Buyer's Guide tab for the full vehicle list.
- Aluminum housing: constructed to match the casting material of the original part for similar performance.
- Fluid-resistant seals: all rubber components use a high-quality EPDM compound that resists glycol-based brake fluid.
- 100% new: built entirely from new materials, not remanufactured.
- Made to SAE International standards with a 1-inch bore and two outlets — a rearward outlet sized M10 x 1.0 and a secondary outlet thread diameter of M12 x 1.0 (primary outlet thread pitch 1 mm).
The reservoir and sensor are included. Mounting hardware is not included — consult the vehicle service information for the correct fasteners and whether they may be reused. Country of origin: China. Manufacturer part number M390186.
Frequently Asked Questions
What does this master cylinder do?
It converts brake pedal force into hydraulic pressure and sends brake fluid to the wheel circuits. If a failed master cylinder is the cause of your brake trouble, this unit replaces it.
Does it include a reservoir and sensor?
Yes. Per the catalog attributes, this master cylinder includes the reservoir and the sensor.
Is mounting hardware included?
No. Mounting hardware is not included, so consult the vehicle service information for the correct fasteners and whether they may be reused.
What vehicles does this fit?
It's a direct-fit replacement for the listed applications, including the 1991-1995 Buick LeSabre and Park Avenue and 1995-1999 Oldsmobile Aurora. Check the Buyer's Guide tab for the full list.
What are signs my master cylinder may need replacing?
A pedal that slowly sinks, feels spongy, or brake fluid leaking near the unit may signal a failing master cylinder. Diagnose the cause before replacing, as other components can produce similar symptoms.
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