What Is brake Master Cylinder ? Working | Applications | Uses |

In this article we will Discuss in Details About What is Master Cylinder ? It’s Working Functions, Applications, Advantages and Disadvantages with Figure.

What is Master Cylinder ?

The Master Cylinder is a Control Device which converts the Force (commonly from a driver’s foot) into the hydraulic Pressure.

Master cylinder

Definition: A master cylinder is a hydraulic device consisting of pistons and cylinders designed to convert mechanical power, applied by the driver through the brake pedal in vehicles or the brake switch in bicycles, into hydraulic force. This hydraulic force is then utilised to activate the brake calliper, enabling the braking action.

It acts as a controller for slave cylinders positioned at the opposite end of the hydraulic brake system. This means that when you press the brake pedal, the master cylinder converts your foot’s force into hydraulic pressure, which then controls the slave cylinders. These slave cylinders activate the brakes, helping the vehicle slow down or come to a complete stop.

history of master cylinder

In a hydraulic braking system, the chamber plays a crucial role in delivering the necessary force or braking power to the final braking stage. This force is generated through the conversion of mechanical power input by the driver via the brake pedal or brake switch.

The chamber operates on the fundamental principle of Pascal’s law, which states that when force is applied to a larger inlet area, a high-pressure fluid is obtained at a smaller outlet area.

Similarly significant to the brake disc/rotor, the master cylinder is an essential component of a disc brake assembly. Typically composed of aluminum or cast iron, it functions in a manner similar to a throttle system.

Just as the throttle supplies fuel to the engine, the master cylinder supplies brake fluid to the caliper assembly under high pressure. This ensures the provision of the necessary braking force to the final braking elements, amplifying the mechanical force applied by the driver on the brake pedal or brake lever.

This system leverages the specific properties of brake fluid, allowing it to operate effectively under high temperatures and pressures. The ideal brake fluid possesses characteristics such as high operating temperature tolerance, suitable viscosity-temperature properties, physical and chemical stability, corrosion protection for metal components, and lubricating effects.

Types of master cylinder

  1. Open system
  2. Closed
  3. Single cylinder
  4. tandem cylinder
  5. Portless master cylinder

#1. Open system

An open system master cylinder assembly comprises of reservoir tanks containing bladders that serve to regulate the brake fluid level within the cylinders. These bladders respond to changes in temperature by expanding or contracting, as one side is exposed to the surrounding environment.

Advantages: The automatic adjustment of the brake fluid level in the master cylinder assembly offers several benefits. It provides protection to the disc brake system from overheating. Additionally, since the brake fluid level is regulated automatically through the bladder’s expansion or contraction, it does not impact braking performance. This means there is no need to manually apply the brakes, as the system operates effectively in an open configuration.

Disadvantages: One drawback of the automatic adjustment feature is that it can cause issues when the brake pads malfunction. In such cases, the open system supplies an excessive amount of fluid to the caliper bore, allowing for adjustment of the malfunctioning pad. If this condition persists for a prolonged period, it can lead to expensive damage to the disc and caliper assembly. Furthermore, the open system may generate brake noise and adversely affect the overall braking performance.

An open system master cylinder with underfilled bladders under vacuum or overfilled bladders under pressure can significantly compromise the braking performance. Consequently, this technology is considered outdated.

# 2. closed

The closed system master cylinder differs from the open system as it lacks a bladder within its reservoir tank. Consequently, this system necessitates manual adjustments.

Advantages: The closed system master cylinder finds extensive usage in various automobile types. It allows for convenient monitoring of the brake fluid level through the reservoir tank, enabling easy detection of dark or inadequate fluid levels. Moreover, in such systems, worn-out brake pads can be readily identified.

Disadvantages: This system is prone to overheating issues. If the brake fluid level deviates from the recommended range, it can adversely affect the braking performance. Additionally, the presence of air anywhere within the system can impact braking efficiency, requiring the bleeding of oil to remove any air pockets.

#3. single cylinder

The single-cylinder serves as the most fundamental form of a master cylinder and shares inherent similarities with a plastic medical syringe. When the brake pedal lever is pressed, it activates the plunger pistons within the cylinders, causing the fluid to flow through the lines and into the slave cylinder. Once the brake pedals are released, springs situated inside the cylinder push the plunger back to its original position.

By employing negative pressure, the brake fluid is drawn from the lines and reservoir into the cylinder. Although automakers have transitioned to more redundant tandem master cylinders, many race car manufacturers still prefer utilizing a pair of single cylinders instead of a single tandem cylinder to regulate the bias of front and rear brake pressure.

#4. Tandem Cylinder

A tandem cylinder is a hydraulic device that incorporates two pistons within a single unit. The primary pistons are directly linked to the brake pedal. When the brake pedal is depressed, the primary piston applies force to a spring located at the rear of the secondary piston. Once the spring is fully compressed, the secondary piston initiates the movement of fluid through its dedicated system.

To ensure consistent pressure on both sides, the reservoir inlets port enables the fluid to flow past the piston. This mechanism helps maintain equilibrium. When the brake pedal is released, the spring’s pressure pushes the piston back, and a small compensating port in the brake fluid reservoir allows for the introduction of excess fluid into the chamber.

The presence of the compensating port is crucial to expedite brake release. Without it, the backward movement of fluid through the lines would impede the release process.

#5. Portless master cylinder

Portless master cylinders, initially introduced on the Toyota MR2, provide a quicker brake release compared to standard designs that utilize a compensating port. Instead of relying on a compensating port, portless cylinders employ a valve assembly within the piston that opens to equalize pressure when the brake pedal is released.

This design eliminates the need for a compensating port, which can restrict fluid flow and decrease initial pressure from the brake system.

The fast-acting portless cylinder demonstrates enhanced performance when paired with an anti-lock braking system (ABS), which employs rapid pressure modulation to fine-tune the braking force.

working of master cylinder

The master cylinder is a vital component of a hydraulic braking system. Its main function is to convert the force exerted on the brake pedal by the driver into hydraulic pressure, which is then transmitted to the wheel brakes to engage them.

Working of master cylinder

The working principle of a master cylinder can be summarized as follows:

  1. Brake pedal activation: When the driver presses the brake pedal, a mechanical linkage transmits the force to the master cylinder. This force is applied to a piston or plunger located within the cylinder.
  2. Piston movement: As the piston receives the force from the brake pedal, it moves forward or downward (depending on the design). This movement creates a hydraulic pressure within the master cylinder.
  3. Fluid displacement: The movement of the piston within the master cylinder displaces the brake fluid stored in the cylinder’s reservoir. This fluid is pushed through the hydraulic lines or brake hoses connected to the master cylinder.
  4. Hydraulic pressure transmission: The hydraulic pressure generated by the master cylinder is transmitted through the brake lines to the wheel cylinders or brake calipers at each wheel. The pressure acts on pistons within these components, causing them to move and apply force to the brake pads or brake shoes.
  5. Brake engagement: The force applied by the brake pads or brake shoes against the rotating brake discs or drums creates friction, which slows down or stops the vehicle.
  6. Brake pedal release: When the driver releases the brake pedal, springs within the master cylinder and other brake components return the pistons to their original positions. This action allows the brake fluid to return to the master cylinder’s reservoir, relieving the hydraulic pressure in the system and releasing the brakes.

Overall, the master cylinder’s working principle relies on the conversion of mechanical force from the brake pedal into hydraulic pressure, which is then used to activate the wheel brakes and enable effective braking of the vehicle.

Parts of Master Cylinder

  1. Reservoir
  2. Cylinder
  3. Piston
  4. Piston assembly
  5. Spring return
  6. Valve
  7. Brake pedal
  8. Brake fluid
  9. Series of gasket
  10. Clamp
Parts of master cylinder


In hydraulic braking systems, the reservoir serves as the storage container for brake fluid. Typically, it is constructed from aluminum, cast iron, or occasionally plastic.

The reservoir is predominantly rectangular in shape, although round-shaped reservoirs are employed specifically for rear disc brakes. Its design allows for convenient monitoring of the oil level and observation of the oil’s color.


The brake system comprises an enclosed chamber that houses the piston, which moves in response to the brake pedal’s pressure, resulting in the conversion and amplification of force. This cylinder is typically constructed from either cast iron or aluminum.

3 Piston

When the brake pedal is depressed, the piston within the cylinder undergoes rotational motion. As a consequence, the piston compresses the brake fluid contained within the cylinder, creating significant hydraulic pressure. The piston of the master cylinder is connected to a push rod and is equipped with return springs.

4 Piston Assembly

The piston assembly consists of various components, including the piston itself, a series of O-rings or gaskets known as cup O-rings, circle P, primary cup, secondary cup, and a return spring. Located in close proximity to the cylinder’s bore, the piston assembly plays a crucial role in the functioning of the master cylinder.

5 Spring Return

A spring installed within the cylinder plays a crucial role in preserving the initial positions of the piston and brake pedal after the release of the brake pedal. This type of spring can be found in both drum brake and disc brake setups.

6 valve

This valve serves as the connection point for the brake line. Its purpose is to facilitate the transfer of compressed brake fluid to the caliper.

7 brake pedal

The brake pedal plays a crucial role within the master cylinder assembly, as it serves as the mechanism through which instructions are given to the master cylinder.

8 brake fluid

Brake fluid, typically a form of hydraulic fluid, holds immense importance similar to engine oil. Its primary function is to enable the vehicle to exert force on the brakes, thereby facilitating deceleration and stopping.

9 Bladder

The bladder is a component commonly found in open system master cylinders. It is typically constructed from thin rubber, allowing it to undergo deformation through expansion and contraction. One side of the bladder contains liquid while the other is exposed to the surrounding atmosphere.

10 series of gasket

The gasket set comprises various components, namely a cup or O-ring, primary cup, secondary cup, and circle P. The cup and circle P serve as retainers for the piston and are positioned between the pushrod and the piston.

The primary seal facilitates the passage of brake fluid from the reservoir into the brake hose pipe when the brake lever or pedal is activated. On the other hand, the secondary seal ensures that the brake fluid remains securely contained and prevents any leakage towards the outer side when the brake pedal is pressed.

symptoms of faulty master cylinder

Here are some common symptoms that may indicate a faulty master cylinder:

  1. Soft or spongy brake pedal: If you notice that your brake pedal feels soft or spongy when you apply pressure, it could be a sign of a failing master cylinder. This can occur due to internal seal leaks or a loss of hydraulic pressure.
  2. Brake fluid leakage: A faulty master cylinder can lead to brake fluid leakage. You may observe fluid pooling underneath the vehicle near the wheels or detect a decrease in the brake fluid level in the reservoir.
  3. Contaminated brake fluid: If the master cylinder is failing, it can allow contaminants such as air, moisture, or debris to enter the brake fluid. As a result, the brake fluid may appear discolored, murky, or contain visible particles.
  4. Brake pedal sinking or going to the floor: When the master cylinder fails, you may experience a situation where the brake pedal sinks to the floor or requires excessive force to engage the brakes properly. This can indicate a loss of hydraulic pressure within the system.
  5. Delayed or unresponsive braking: A faulty master cylinder can cause delayed or unresponsive braking. You may notice a delay between pressing the brake pedal and the brakes actually engaging, or the brakes may not respond effectively to pedal input.
  6. Brake warning light: In some cases, a failing master cylinder can trigger the brake warning light on the dashboard. If this light illuminates, it is important to have the braking system inspected and repaired promptly.

It’s important to note that these symptoms can also be caused by other issues within the braking system, so it is advisable to have a professional mechanic diagnose the problem for an accurate assessment and proper repairs.

functions of master cylinder in Automobiles

The master cylinder plays a crucial role in the hydraulic braking system of an automobile. Its primary functions can be summarized as follows:

  1. Brake Force Amplification: The master cylinder amplifies the force applied by the driver on the brake pedal. When the driver presses the pedal, it exerts a mechanical force on the master cylinder, which converts it into hydraulic pressure.
  2. Hydraulic Pressure Generation: The master cylinder generates hydraulic pressure using the force received from the brake pedal. This pressure is created by the movement of a piston or plunger within the cylinder. The hydraulic pressure is essential for transmitting force to the wheel brakes.
  3. Brake Fluid Distribution: The master cylinder distributes brake fluid to the individual wheel brakes. It stores brake fluid in a reservoir and displaces it when the brake pedal is pressed. The pressurized brake fluid is then sent through brake lines or hoses to the wheel cylinders or brake calipers.
  4. Hydraulic Pressure Transmission: The generated hydraulic pressure is transmitted through the brake lines to the wheel brakes. It acts on the pistons within the wheel cylinders or calipers, causing them to exert force on the brake pads or brake shoes. This force creates friction against the rotating brake discs or drums, resulting in deceleration or stopping of the vehicle.
  5. Hydraulic Pressure Release: When the brake pedal is released, springs within the master cylinder and other components return the pistons to their initial positions. This action allows the brake fluid to return to the master cylinder’s reservoir, relieving the hydraulic pressure in the system and releasing the brakes.

Overall, the master cylinder serves as a vital component in the hydraulic braking system of an automobile. It converts the mechanical force from the brake pedal into hydraulic pressure, ensuring effective transmission of braking force to the wheel brakes, thus enabling safe and reliable vehicle braking.

Advantages of master Cylinder

Advantages of the master cylinder in vehicle braking systems:

  1. Efficient force conversion from foot to hydraulic pressure.
  2. Multiplies force for increased hydraulic pressure.
  3. Controls pressure distribution for balanced braking.
  4. Incorporates safety features for stability and control.
  5. Durable and reliable performance.
  6. Compatible with power brake systems for added braking power.

Disadvantages of Master Cylinder

Disadvantages of the master cylinder in vehicle braking systems:

  1. Fluid leaks can occur, affecting brake performance.
  2. Susceptible to corrosion, potentially compromising functionality.
  3. Contamination of brake fluid may impact braking ability.
  4. Complex repairs requiring specialized knowledge.
  5. Costly replacement if the master cylinder fails.
  6. Brake pedal feel issues can arise.

Source :- https://en.m.wikipedia.org/wiki/Master_cylinder

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