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The most risky maintenance item to postpone on a car is the brakes. Neglecting something engine-related usually costs you money; neglecting something brake-related costs you stopping distance. That's why the brake system occupies a different place on the maintenance list than other items.

How does the brake system work?

Brakes are a system that converts kinetic energy into heat. When you press the pedal, the master cylinder pressurises the hydraulic line. This pressure reaches the callipers, and the calliper presses the brake pads against the rotating disc. The friction between the pad and the disc converts the vehicle's speed into heat, and this heat is released into the air through the disc.

This description also reveals the system's three weak points: friction surfaces wear down, heat fatigues components, and the hydraulic line has to transmit pressure accurately. Brake maintenance is the inspection of these three points.

Signs of brake pad wear

The brake pad is, by design, a wearing part; its friction surface gradually thins over time. The signs of wear are generally as follows:

• A metallic screech or continuous whistling sound: Many pads carry a wear indicator element that touches the disc and makes a noise once the friction material has worn down to a certain limit. This sound means "have it checked now", not "soon".
• Brake pad warning light: On vehicles with an electrical wear sensor, a warning appears on the instrument panel.
• A stiffer pedal or reduced braking power: If you need to apply more force for the same deceleration, the system is warning you.
• The vehicle pulling to one side under braking: This usually indicates uneven wear between the two sides or a calliper sticking.
• A burning smell: A sharp, hot smell, particularly after long descents, indicates overheating.

How much of the pad remains can also be checked visually, but the limit value for the remaining thickness varies by vehicle. For this reason, thickness measurement should be carried out against the minimum value specified by the manufacturer.

Why is disc wear a separate issue?

The brake disc is a part that wears more slowly than the pad, but it inevitably wears, and it deteriorates in two different ways:

• Thickness loss: Every braking event removes a certain amount of material from the disc as well. When the disc's thickness drops below the minimum value set by the manufacturer, the disc can no longer carry heat safely and needs to be replaced. This value is usually stamped on the hub of the disc.
• Run-out and surface deterioration: When the disc is no longer flat, its contact with the pad varies rhythmically. The typical sign of this is vibration in the pedal under braking and a recurring judder in the steering wheel. If deep scoring, pitting, or a pronounced lip has formed on the surface, the pad cannot make full contact and braking efficiency drops.

Fitting new pads to a worn disc is a common but mistaken shortcut. The new pad is forced to bed in against the deteriorated surface, and the result is usually premature wear, noise, and vibration. The condition of the pad and the disc should be assessed together.

There is also the pattern of wear to consider. If the pad on one side is noticeably more worn than the other, it suggests the calliper piston or slider pins are sticking. In this case, simply replacing the pad does not solve the problem; it recurs shortly afterwards.

Why does brake fluid need changing?

Brake fluid is one of the few fluids that needs changing even though it isn't a friction part. The reason is chemical: commonly used brake fluids are hygroscopic, meaning they draw moisture from the air into themselves over time. Even though the system appears sealed, some moisture inevitably accumulates.

Think of why this matters this way: hydraulic fluid doesn't compress, so it transmits the force on the pedal directly to the calliper. Water vapour, however, does compress. Brake fluid enriched with water has a lower boiling point. On a long descent or with repeated hard braking, when brake temperature rises, if the moisture in the fluid vaporises, a compressible bubble can form inside the line. When you press the pedal, the pressure compresses this bubble instead of reaching the calliper. What the driver feels is the pedal going unusually low and becoming spongy — in other words, the loss of braking power.

Moisture also causes corrosion in the system's metal internal components and can affect expensive parts, including the ABS unit. These two reasons are why brake fluid needs to be changed "even though it hasn't run low". Since the replacement interval varies by brand and fluid type, it wouldn't be accurate to give a figure here; the measure is your vehicle's owner's manual.

What does it mean if the level drops?

The brake fluid level drops for two reasons. The first is normal: as the pad thins, the calliper piston moves further out and draws part of the reservoir into the line. The second is not normal: there is a leak in the system. It isn't right to make this distinction by guesswork. If the level warning has come on, or there is a visible drop in the reservoir, the system needs to be checked. Brake fluid is also a liquid that damages paintwork, so care must be taken not to overfill or spill it.

Conclusion

Brake maintenance is more about inspecting the whole than replacing a single part: the remaining thickness of the pad, the thickness and flatness of the disc, the free movement of the calliper, the condition of the hoses, and the quality of the fluid together give the full picture. A change in noise, vibration, pulling, or pedal feel is the system giving you an early warning, and these warnings don't fade over time — they grow.

If you are experiencing any of the symptoms described above with your brakes, you can book an appointment for an inspection. A brake check takes little time, and it is one of those rare maintenance items whose scope only grows the longer it is postponed.