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Your Brake fluid worn out? » Read more about common malfunctions • Repair • Replacement manual
Transfer force to the brake disc
Brake fluid is part of a vehicle's hydraulic braking system. The operating principle is simple: Unlike gasses, fluids cannot be compressed. Thus, if a closed, fluid-filled pipe system is pressurized, the pressure is almost entirely transmitted. Thus, the pressure exerted on the pedal is transferred to the brake pad and brake disc via the brake fluid.
The path of braking force
The braking force begins at the pedal. At this point, a lever system already causes an amplification of force. In addition, the brake pedal opens a vacuum valve, which uses the natural air pressure to increase the braking force. This is the brake booster found in the engine compartment, usually in the form of a can painted black. The brake booster now effects the brake master cylinder. This is where the system filled with brake fluid starts. Force is transferred from the brake master cylinder to the four wheel cylinders via the brake lines. From there, the force is passed to the brake shoes or brake pads to the brake drums or brake discs via small hydraulic cylinders.
Braking system defects
Naturally, brake fluid is of particularly great importance in the power transmission system. If it fails to fulfill its function, the consequences to the vehicle's driving safety will certainly be tragic. Braking force can be lost in two ways: Damage to the braking system or aging of the brake fluid.
Braking system components that can be the cause of issues in aging vehicles are brake lines and seals. Brake lines are made of copper and prone to rusting through, if not properly protected. In this case, brake fluid will leak and no longer transmit force to the brake system. Seals in the brake master and wheel cylinders can also become defective. Brake oil is slightly acidic and therefore gradually attacks the rubber seals on the piston. However, in a braking system, the brake pads and discs or drums are most prone to wear and tear. Also, brake fluid itself can become unusable over time. Brake fluid must reliably transfer the force, even at high temperatures that can occur at the wheel brake cylinders during the braking process. Therefore, water is not suitable for use in braking systems. Unfortunately, brake fluid is hygroscopic. This means that it attracts water in a similar fashion as salt or sugar. If the water content increases over a certain time period, consequences when braking can be fatal: The high temperatures occurring at the brake cause the dissolved water to boil. As a result, it changes from a liquid state to a gaseous state. Gasses, however, can be compressed, unlike liquids. The result can be sudden loss of braking force. Important notes on brake fluid Thus, the water content of brake fluid is crucial for its quality. If the fluid is too old, it changes from a clear, brown color to a dull green. However, this indicates that it is already heavily diluted with water. Even brake fluid that still appears flawless may already have become unusable due to its water content. Only a test provides clarity regarding the condition of the brake fluid. Respective devices are available on the market for 10-50 euro. The best time for checking brake fluid is the beginning and end of the winter season. It can easily be checked when changing tires. In addition to the brake fluid's water content, one should also check the fill level. In a faultless system, the brake fluid's fill level does not change. If a loss is detected, the entire braking system must immediately be checked. The leak must be found and repaired before the car is reintroduced to regular traffic. Simply refilling is not an appropriate measure in this case. Changing brake fluid involves fully bleeding the braking system. Mistakes must be avoided. If the necessary knowledge and tools are not present, it is imperative to have this task performed in a specialist workshop. A checked and overhauled braking system provides the necessary feeling of safety when driving.