Subtle Signs (requiring investigation):
* Spongy or soft brake pedal: This is a classic sign. The pedal feels mushy and doesn't offer firm resistance when pressed. This indicates a loss of hydraulic pressure. It's crucial to distinguish this from simply needing new brake pads; a truly spongy pedal suggests a problem beyond the pads.
* Low brake fluid level: Check your brake fluid reservoir. A consistently low level, especially if it's not explained by recent brake work, strongly points towards a leak *somewhere* in the braking system, and the master cylinder is a prime suspect.
* Brake pedal going to the floor: While this is more dramatic (see below), a slow leak might gradually lead to this. You might notice the pedal getting progressively lower over time.
Obvious Signs (immediate concern):
* Brake pedal goes completely to the floor: This means you've almost entirely lost braking power. This is a very dangerous situation and requires immediate attention; do *not* drive the car.
* Brake fluid leak under the master cylinder: You might see brake fluid leaking from the master cylinder itself, typically around its mounting bolts or seals. Brake fluid is typically a dark brownish color.
* Unusual noises: While not always indicative of a *broken* master cylinder, unusual squeals or grinding noises from the brake system while braking should be investigated. A failing master cylinder *might* contribute to these, especially if other components are already wearing.
* ABS warning light (if equipped): While the ABS system is separate, a serious master cylinder failure *can* trigger this light.
Important Note: If you suspect your master cylinder is failing, *do not drive the car*. A complete failure of your braking system is extremely dangerous. Have the car towed to a qualified mechanic for diagnosis and repair. Do not attempt to repair a master cylinder yourself unless you have extensive mechanical experience and the proper tools. Incorrect repair can lead to serious injury or death.
