84514095 | Genuine GM® Brake Master Cylinder Assembly For Chevrolet, GMC

1. Convert Pedal Force into Hydraulic Pressure

   • Pressing the brake pedal pushes the pistons inside the master cylinder, forcing brake fluid through the brake lines.

2. Distribute Pressure to Wheels

   • Ensures the correct amount of pressure is sent to the front and rear brakes for balanced stopping power.

3. Maintain Brake Fluid Reservoir

   • Holds extra brake fluid to compensate for pad/shoe wear and thermal expansion.

4. Enable Modern Safety Systems

   • Works with ABS, ESC, and other electronic braking systems by providing stable hydraulic pressure.

1. Spongy or Soft Brake Pedal

The pedal feels squishy, sinks slowly, or goes nearly to the floor when pressed.
Usually caused by internal seal wear or fluid bypassing inside the master cylinder.
Air in the brake lines can cause similar symptoms, but if bleeding doesn’t fix it — the master cylinder may be the culprit.

2. Brake Fluid Leak

Look for wet spots or leaks near the master cylinder (usually where it meets the brake booster or around the fittings).
A leaking cylinder reduces hydraulic pressure → weak braking performance.

3. Brake Warning Light On

The dashboard BRAKE or ABS light may turn on if there’s a drop in fluid pressure or imbalance between circuits.
This can indicate internal failure in the master cylinder.

4. Poor Braking Performance / Increased Stopping Distance

The vehicle takes longer to stop, even when pressing the pedal firmly.
Caused by loss of hydraulic pressure or fluid bypass inside the cylinder.

5. Uneven Braking or Pulling to One Side

If one brake circuit isn’t building enough pressure, one side (front or rear) may not brake properly.
This creates an imbalance and can cause the car to pull to one side when braking.

6. Brake Fluid Contamination

Dark, dirty, or rubbery brake fluid can indicate internal seal breakdown inside the master cylinder.
This debris can damage other brake components as well.