Brake Master Cylinders & Reservoirs

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Brake Master Cylinders: Explained

Brake master cylinders transform the applied force on the brake pedal into hydraulic pressure by sourcing fluid from the reservoir and feeding it into the brake circuit. The process is controlled through mechanical force.

Types of Brake Master Cylinders

There are two types of master cylinders including the simple and tandem versions. The difference lies in the number of pistons each cylinder contains. Simple cylinders include only one piston, while tandem cylinders integrate two pistons which generate more braking power through higher hydraulic pressure.

What are Integral Reservoir Master Cylinders?

Integral reservoir master cylinders incorporate a reservoir and a precisely engineered cylinder in one piece to increase efficiency and performance. They feature a slim aluminum design, anodized finish and dual mounting bolt systems which makes them suitable for racing cars. Their exterior return spring guarantees a strong pedal feel and decreases pad wear. Most applications integrate built in fill tabs which allow you to easily check fluid levels. However, a special category includes the race car master cylinders which are specifically engineered to withstand the extreme requirements and conditions of F1 or rally competitions. They’re lightweight and made of aluminum alloy and their lean design makes them easy to install in race cars where space is extremely limited.

How do Master Cylinders and Reservoirs Work?

All modern cars include twin hydraulic circuits and two master cylinders which produce hydraulic pressure in turn in case one of them shuts down. Depending on the car manufacturer, one circuit controls the rear brakes and the other one the front brakes, or one circuit controls all four brakes and the other only the front brakes or each circuit controls one rear brake and the two front brakes. If one of the circuits fails due to a leak, the pressure between the primary and secondary cylinders instantly decreases. This leads to contact between the primary and secondary cylinders and in turn the brake master cylinder will behave as if it only has one piston. Although the second circuit is intact, you’ll have to press harder on the brake pedal to activate it. However, the brake power will be significantly lower than normal. In neutral position, the replenishment port and bore holes of the piston achieve the compensation between the wheel brake and the fluid reservoir. The central valve closes when the brake is activated and interrupts the link between the wheel brake and the reservoir resulting in an increase of pressure. When you release the pedal, the circuit’s pressure decreases which in turn releases the wheel brakes. When the piston returns to neutral it creates a vacuum which allows for the brake fuel to replenish via central valve which is open.

Checking the Brake Fluid Level

To maintain the proper functioning of your car’s brake system you should regularly check and replace the brake fluid. Also, you should keep the ventilation hole on top of the reservoir as clean as possible to prevent contaminants from penetrating into the fluid. To check the fluid level in the reservoir you should check the line on the dipstick and make sure it’s between add and full. If it’s below the add mark, then you probably have a leak in the brake system. You should also verify if the liquid is clear or dark. Dark fluid is an indication that it’s contaminated, and you should get the system flushed.

Safety

The brake system is a crucial component which determines a car’s safety levels. That’s why manufacturers only integrate tandem master cylinders in today’s vehicles. If one of the brake circuits fails, the other will take over and prevents any incidents. Although master brake cylinders are made from top-quality materials they can depreciate in time. You should regularly check your car’s braking system to ensure its functions at optimal levels and to avoid any accidents.

Frequently Asked Questions about Brake Master Cylinders & Reservoirs

What does a bigger brake master cylinder do?

A bigger brake master cylinder increases the volume of brake fluid that can be pushed through the braking system. This can lead to several benefits:

  • Improved Brake Response: A larger cylinder can provide a quicker response when the brake pedal is pressed.
  • Increased Brake Force: It can generate more hydraulic pressure, enhancing the overall braking force applied to the wheels.
  • Better Performance with Larger Brakes: If larger brake calipers or rotors are installed, a bigger master cylinder can help maintain optimal performance.
  • Reduced Pedal Travel: It can decrease the distance the brake pedal needs to be pressed to achieve effective braking.

What does a brake master cylinder do?

The brake master cylinder is a crucial component of a vehicle's braking system. Its primary functions include:

  • Fluid Pressure Generation: It converts the force applied to the brake pedal into hydraulic pressure.
  • Brake Fluid Distribution: It distributes brake fluid to the brake calipers or wheel cylinders at each wheel.
  • System Monitoring: It often includes a reservoir to maintain the brake fluid level and may have a warning system for low fluid levels.
  • Dual Circuit Design: Many master cylinders have a dual circuit design for safety, ensuring that if one circuit fails, the other can still function.

How much does it cost to fix bleeding brakes?

The cost to fix bleeding brakes can vary based on several factors, including the make and model of the vehicle and the labour rates in your area. Generally, you can expect the following costs:

  • DIY Bleeding: If you choose to bleed the brakes yourself, the cost may be minimal, typically around £10 to £30 for brake fluid.
  • Professional Service: Hiring a mechanic can cost between £50 and £100, depending on the garage and the complexity of the brake system.
  • Additional Repairs: If there are underlying issues (e.g., leaks or damaged components), costs can increase significantly, potentially ranging from £100 to £500 or more.

How often should you bleed your brakes?

Bleeding your brakes is essential for maintaining optimal braking performance. It is generally recommended to bleed your brakes:

  • Every 1-2 years as part of regular maintenance.
  • Whenever you replace brake components, such as calipers or brake lines.
  • If you notice a spongy brake pedal or reduced braking performance.
  • After any brake fluid contamination or leaks.
Always refer to your vehicle's owner manual for specific recommendations related to your make and model.

What do brake bleeders do?

Brake bleeders are essential components in a vehicle's braking system. Their primary function is to remove air bubbles from the brake lines, ensuring that the brake fluid can flow freely and effectively. This process is crucial for maintaining optimal braking performance. Key functions of brake bleeders include:

  • Allowing for the expulsion of air trapped in the brake lines.
  • Facilitating the replacement of old brake fluid with fresh fluid.
  • Ensuring consistent brake pedal feel and responsiveness.
  • Preventing brake system failure due to air contamination.
Properly functioning brake bleeders contribute to the overall safety and efficiency of a vehicle's braking system.

What is the best material for brake lines?

The best materials for brake lines are:

  • Stainless Steel: Highly resistant to corrosion and offers excellent durability. Ideal for high-performance vehicles.
  • Copper-Nickel Alloy: Combines the benefits of copper and nickel, providing good corrosion resistance and flexibility.
  • Rubber: Commonly used for flexible brake lines, it offers good flexibility but may degrade over time due to heat and exposure to brake fluid.
  • PTFE (Polytetrafluoroethylene): Known for its chemical resistance and low friction, often used in high-performance applications.

How often should I change brake fluid?

It is generally recommended to change brake fluid every 2 years or 24,000 miles, whichever comes first. However, this can vary based on the vehicle manufacturer’s guidelines and driving conditions.

  • Check the owner's manual for specific recommendations.
  • Inspect brake fluid regularly for contamination or moisture.
  • Consider changing brake fluid more frequently if driving in harsh conditions.

What is a brake duct?

A brake duct is a component used in vehicles to enhance the cooling of the brake system. It directs airflow towards the brake components, helping to dissipate heat generated during braking. Key functions of brake ducts include:

  • Improving brake performance by maintaining optimal temperatures.
  • Reducing the risk of brake fade, which can occur when brakes overheat.
  • Extending the lifespan of brake components by preventing excessive heat buildup.
Brake ducts are commonly found in high-performance and racing vehicles, but they can also be beneficial in regular road cars, especially in demanding driving conditions.

Does anti-roll bar affect steering?

Yes, an anti-roll bar can affect steering. It plays a crucial role in maintaining vehicle stability during cornering, which indirectly influences steering response. Effects of an anti-roll bar on steering include:

  • Improved Handling: By reducing body roll, the anti-roll bar helps keep the tyres in better contact with the road, enhancing grip and steering precision.
  • Steering Feedback: A stiffer anti-roll bar can provide more direct feedback to the driver, making the steering feel more responsive.
  • Understeer/Oversteer Balance: The design and stiffness of the anti-roll bar can influence the balance of the vehicle, potentially leading to understeer or oversteer, which affects steering behaviour.

Is an anti-roll bar necessary?

An anti-roll bar, also known as a sway bar, is not strictly necessary for a vehicle to operate, but it plays a significant role in enhancing handling and stability. Benefits of an anti-roll bar include:

  • Improved Handling: It reduces body roll during cornering, allowing for better control.
  • Increased Stability: It helps maintain a level stance, improving traction and grip.
  • Enhanced Safety: By minimising roll, it can prevent loss of control in sharp turns.
While some vehicles may perform adequately without one, especially in everyday driving conditions, an anti-roll bar is particularly beneficial for performance-oriented cars or those frequently driven in challenging conditions.

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