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  • Writer's picturejianmei huang

Everything You Need To Know About Brake Fluid

Updated: Feb 29

In fact, for many of the people who - at least - dare to open the hood and do a very basic mechanical check, the brake fluid is nothing more than "that thing that should not be touched because they already look at it in the workshop." Indeed, the lubricating oil cap should not be confused with the antifreeze cap, the power steering fluid cap, or the windshield washer cap. Everything you need to know about brake fluid so that you do not neglect a detail of an essential issue for safety.

Key Components of a Braking System

The braking system in a car is a generally double, sealed hydraulic circuit designed for safety, consisting of:


Brake fluid reservoir: This is a small translucent bucket with a logo similar to the one you see here.


Liquid: It is a specific fluid for this function. It must be in good condition and not mixed with anything. As a general rule, we recommend that you stick to the specifications recommended by the manufacturer.


Pedal: The central pedal activates the so-called service brake, which causes the liquid to push the elements that enable braking in a fundamentally mechanical way and to do so hydraulically.


Bomb: As automobiles evolved, the driver no longer had to operate a lever that rubbed against the wheel, as was done in early models; The braking process began with the foot, as now, thanks to the pedal pumping and the fluid pushing. To facilitate this, elements were developed to help with this, so that the driver did not have to exert so much pressure and braking ended up being more pleasant, but, above all, more effective.


Brake Servo: One of the key advances. This element allowed the driver's force to be multiplied when pressing the pedal.


Switchboards: The arrival of electronics made braking more effective and safer, regulating the intensity based on the demand for force and road conditions in real time.


ABS: it is more than half a century old and continues to be one of the best inventions in terms of safety. The anti-lock brake system is activated when emergency braking is carried out, in such a way that the control unit 'orders' to brake and not brake many times per second. This causes the wheels to lock, the stopping distance to be reduced and the driver to be able to maintain direction and avoid an obstacle.


Channels: these are the 'tubes' through which the brake fluid runs.


Hoses: This is the name given to the last part of the ducts, which go to the brake calipers or the brake shoe cylinders. They are flexible, rubber or metal.


Calipers, pads, and discs: In disc brakes, the calipers are actuated by fluid pressure. When closed, the pads on their internal faces are what exert rolling resistance on the discs.


Drums: In drum brakes, the pressure of the brake fluid activates the cylinders, which transmit the force to the shoes and rub against the inner face of the drums.


The handbrake is not usually associated with this hydraulic circuit, since it is normally activated separately, using a mechanical or electronic system.


Like any fluid, brake fluid also ages and can suffer pressure losses due to leaks in the circuit or aging of the fluid itself. In both cases, the consequences can be very dangerous.

When to Refresh Brake Fluid

Whether in a workshop or on your own, it is worth taking a look at the brake fluid from time to time, preferably more frequently than indicated in the maintenance book. What needs to be checked?


Level: in the glass that contains it, the level must be between the maximum and the minimum, but closer to the line that indicates the former.


Glass: it must be watertight and have no jets or drips.


Cap: that it is in good condition and correctly closed, without cracks.


Age: check that the brake fluid is not older than 2-3 years since its last replacement.


Ducts: the same must happen in the rest of the installation. Make sure that neither internal ducts nor 'peripheral' elements (brake servo, ABS...) have leaks.


Hoses: these elements are some of the most exposed to deterioration, especially if they are made of rubber instead of metal (more expensive, but also more resistant. You must make sure that there are no cracks, cracks, leaks...


Seized cylinders (in drum brakes): this is more difficult to see with the naked eye and usually shows up in the MOT when the braking is unbalanced between one side of the vehicle and the other.


Central pedal: if you notice a 'strange' operation, it may be a sign of leaks, loss of pressure, air in the circuit... Examples: you should not notice that the brake is too hard or too soft. Nor, that when you leave your foot pressing the central pedal (on a hill or at a traffic light), it 'sinks' little by little. If you notice an irregular or 'spongy' feel, also go to the workshop immediately: there could be leaks or even air in the circuit!


When purchasing brake fluid, it's best to follow the manufacturer's recommendations for your specific car model. However, there are different types of products (DOT 3, DOT 4, DOT 5...) classified according to their boiling point, viscosity, duration and properties. As with all products, prices vary slightly.


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Brake fluid is essential for vehicle safety, requiring regular checks and replacement every 2-3 years. Adhering to manufacturer guidelines and being alert to changes in brake pedal feel or visible leaks is crucial for maintaining effective braking performance and ensuring road safety.




What is the main function of brake fluid in a car's braking system?

Brake fluid is essential for transmitting the force applied on the brake pedal to the brake calipers or shoe cylinders, enabling effective braking.


How often should brake fluid be checked or replaced?

Brake fluid should be checked regularly, preferably more frequently than suggested in the maintenance book, and replaced every 2-3 years.


What are some signs of potential issues with brake fluid or the braking system?

Indicators of problems include a brake pedal that feels too hard or soft, a pedal that sinks gradually when pressed, visible leaks in the system, or a spongy feeling when braking.

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