Brake System Basics
How hydraulic pressure becomes braking force, and what wears out.
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What you will learn
- Explain the hydraulic principle
- Describe disc and drum brakes
- List the main wear items
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Pressing the pedal moves a piston in the master cylinder, which pushes brake fluid through lines to the calipers or wheel cylinders. Because liquids are essentially incompressible, the force is transmitted almost undiminished, and the hydraulic ratio multiplies it.
At the wheel, hydraulic pressure squeezes the pads against a rotating disc (or shoes against a drum). Friction converts motion into heat, which is why brakes glow and fade when abused. Air in the fluid, a seized caliper or worn pads all change pedal feel and stopping distance.
| Item | What it does | Wear sign |
|---|---|---|
| Pads / shoes | Create friction | Thickness, squeal, grinding |
| Discs / drums | Friction surface | Scoring, lipping, thickness |
| Brake fluid | Transmits force | Moisture, dark colour, soft pedal |
| Calipers / cylinders | Apply the pads | Seizing, leaks, uneven wear |
| Hoses / lines | Carry fluid | Cracking, swelling, leaks |
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Brake fluid absorbs moisture and must be replaced on schedule. A soft or spongy pedal means air or a leak — do not road test until it is resolved.
Key points
- Hydraulics multiply pedal force and cannot be compressed.
- Brakes turn motion into heat; fade is overheating.
- Consumables wear together — inspect as a system.
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Key points
- Brakes convert motion into heat
- Fluid transmits force, not compressible air
- Pads, discs and fluid are consumables
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.
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