Brake - head cylinder: function, replacement and purchase of the master cylinder in the car

The brake master cylinder is one of the most important parts of modern car brake systems. Here, the component has the function of converting the mechanical pressure on the brake pedal into hydraulic brake pressure. Also known as the master cylinder, this brake component is used in both disc brakes and drum brakes. Car parts that are subjected to a lot of stress, such as the brake master cylinder, can wear out and break down over the years. If the first signs of a defect in the component appear, such as decreasing brake pressure, the master cylinder must be replaced.

How the master cylinder works in the brake system

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A brake master cylinder consists of several components such as a cylinder housing and the balance reservoir as a refill reservoir for the brake fluid. It is usually located in the engine compartment above the driver’s footwell and in close proximity to the brake pedal. In a modern vehicle, the brake master cylinder is often flanged directly to the brake booster.

The brake master cylinder consists of a metal cylinder in which a piston rod moves. Firmly connected to the rod are sleeves as sealing elements, which thus act as pressure pistons within the cylinder. The brake pedal in the car is coupled to the outside of the piston rod. When the driver of the car steps on the pedal, the rod is set in motion.

In this way, pressure is created in the pressure chamber of the cylinder, which is transmitted to the brakes via brake lines. Here, the pressure acts on the wheel brake cylinders of the drum brake or the brake pistons of the disc brake, and applies the brake. When the driver takes his foot off the brake pedal, a return spring initiates the release of pressure, ending the braking process.

The tandem master cylinder for two brake circuits

Modern cars today have two separate brake circuits, both of which are operated by the same master cylinder as a tandem master cylinder. If the vehicle had only one brake circuit, no braking power would be available in the event of a circuit failure. Instead, one brake circuit cross-controls one brake at the front and one brake at the rear.

In the tandem master brake cylinder, two master brake cylinders are arranged in a common housing. If one brake circuit is defective, for example because brake fluid leaks, the second brake circuit is still available. Thanks to the tandem master cylinder and modern dual-circuit brake system, the vehicle can still be stopped effectively in this case.

If the master cylinder is defective

Due to various causes, the master cylinder may fail or be limited in its function. In this case, there is no longer sufficient braking force available to brake the vehicle safely in extreme situations. A car with defective or limited brakes should not be moved under any circumstances. Defective brake master cylinders must be replaced with suitable spare parts as soon as possible.

If symptoms such as a drop in brake pressure or poor brake performance are apparent, this may indicate a defective master brake cylinder. In addition to a defective master brake cylinder, however, defective brake shoes, worn brake discs, worn brake pads of the drum brake, a cracked expansion tank or a defective brake caliper are also possible causes. If there are signs that the brakes are defective, the vehicle should definitely be checked by a specialist.

Typical symptoms of a defective brake master cylinder

• Braking force is noticeably reduced
• The brake pedal does not come back
• Pedal travel is unusually long
• Pressure in the brake system drops rapidly
• Error message in the driver display

Replace the brake system master cylinder

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If brake master cylinders are defective, they must be replaced with intact spare parts. As a rule, the cylinders cannot be repaired. Like all work on the brake system, replacing the master cylinder is a professional matter and should only be carried out by really skilled car mechanics.

Depending on the model and manufacturer, the procedure for changing the master cylinder may differ. The brake fluid from the expansion tank should be sucked out, and any brake fluid that escapes when the cylinder is removed should also be collected. After loosening the brake lines and the fastening screws, the defective master cylinder can be removed.

An intact brake master cylinder is then fitted in reverse order. Used master cylinders are often supplied complete with a reservoir, otherwise the old refill reservoir can be used. Once the master cylinder has been installed, brake fluid must be added and the brake system bled.

Four common causes of defective brake cylinders

1. Wear on the brake master cylinder: The car’s service brakes are applied many times every time the car is driven. Therefore, the components inside the cylinder can wear out over time, leading to a defect in the component.
2. Ageing of the material: The brake master cylinder has sleeves and sealing elements inside. These elastic parts can harden or become brittle over the years, causing leaks to form.
3. Corrosion on the brake master cylinder: On some vehicle models, the brake master cylinder is positioned in such a way that it is exposed to high loads from splash water or road salt in winter. In this case, corrosion can occur on the brake master cylinder, which damages the part.
4. Brake fluid has not been changed: If the brake fluid in the vehicle is not changed at regular intervals, this not only reduces the braking effect in dangerous situations. In this case, parts of the brake system such as the brake master cylinder can also wear out due to corrosion on the inside.

Buy suitable parts for the brake system on your vehicle

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If components of the brake system are defective, a timely replacement is essential. At Autoparts24 you will find numerous brake system components for your vehicle. Depending on the manufacturer, suitable brake master cylinders can differ in diameter or thread size.

It is therefore important to select the right type. To list all suitable brake components such as brake master cylinders, simply enter the manufacturer and vehicle model. Alternatively, you can enter the key numbers from the vehicle documents to find the right spare part.

Convenient price comparison possible

If you would like to buy components such as a master brake cylinder, it is worth comparing prices. All fitting OEM replacement parts for your vehicle are clearly displayed at Autoparts24 so that you can choose from numerous offers. All used parts come from certified car recycling, and are listed with detailed photos as well as additional information such as model variant and year of manufacture.

Advantages of buying used car parts

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If you buy parts such as the brake master cylinder used, you can sometimes save a lot of money. In addition, this way you get original spare parts that correspond to the parts installed on the vehicle in all respects. In addition, buying used spare parts protects the environment because the purchased parts do not have to be produced anew.