Hydraulic brakes: Basics, Principle, Working, Advantages and Disadvantages

Hydraulic brakes: Basics, Principle, Working, Advantages and Disadvantages

The brakes or the system of braking mechanism which are operated and applied by liquid or oil pressure from controlling mechanism to braking mechanism in order to slow down or completely stop the vehicle is known as hydraulic brakes. In simple language, hydraulic brakes are brakes that use oil pressure for braking action. In this article, we will cover the Basics, Principles, Working, Advantages, and Disadvantages of hydraulic brakes.

What are the main parts of hydraulic brakes?

Hydraulic brakes: Basics, Principle, Working, Advantages and Disadvantages

The main parts of hydraulic brakes are:

1) Master cylinder:

Master Cylinder in Hydraulic Brakes

The master cylinder, also known as the master brake cylinder, converts the pressure on the brake pedal to hydraulic pressure by feeding brake fluid into the brake circuit and controlling this according to the mechanical force. Disc and drum brakes, both use a master cylinder.

2) Brake lines:

Brake lines are tubes that carry fluid between brake components. Brakes translate the pressure from your foot on the brake pedal into stopping power.

3) Brake pedals in hydraulic brakes:

The brake pedal is the pedal that you press with your foot in order to make a vehicle go slower or stop accordingly with respect to the force applied to the brake pedal.

4) Braking action by Disc/drum (Near wheels):

Different types of brakes (Disc and drum) that slow down the vehicle by the pressure of oil or fluid/ by generating hydraulic pressure directly applied to the wheel brakes.

5) Wheel cylinder in hydraulic braking system:

It is a different cylinder than the master cylinder. It is the cylinder of the wheel. Located in each wheel. Its function is to exert force onto the shoes so as to bring them into contact with the drum and stop the vehicle with friction.

6) Brake fluids:

The common brake fluids used for hydraulic brakes are DOT3, DOT4, DOT5, etc. For instance, DOT3 DOT4 and DOT5 are glycol ether-based which generally means that they absorb moisture from the atmosphere.

However, liquid pressure helps in the application of hydraulic brakes. The transmission of pedal force to the brake shoe with the means of a confined liquid through a system is brake fluid. The force applied to the pedal multiplies and transmits to all the brake shoes by a force transmission system. This system is based upon Pascal’s principle, which states that “the confined liquids transmits pressure without loss equally in all directions”.

Essentially there are two main components, master cylinder, and wheel cylinder. The master cylinder is connected by tubing to the wheel cylinders at each wheel. The system is filled with light pressure when the brakes are not in operation. However, the liquid is known as brake fluid.

Each wheel brake consists of a cylinder brake drum mounted on the inner side of the wheel. The wheel brake revolves with the wheel but two brake shoes mounted inside the brake drums do not rotate. The brake shoes consist of heat and wear-resisting brake lining on their surfaces.

How Hydraulic Brakes system work?

The brake pedal is connected to the master cylinder piston by means of a piston rod. When we apply brakes or when we press the brake pedal, the piston forces into the master cylinder, which increases the pressure of fluid inside the master cylinder and in the entire hydraulic system. This pressure is conducted instantaneously to the wheel cylinders on each of the four brakes, where it forces the wheel cylinder pistons outwards.

These pistons, in turn, force the brake shoes out against the brake drums. Hence, brakes are applied.

When we release the brake pedal, the master cylinder piston returns to its original position due to the return spring pressure. Thus, the fluid pressure inside the entire system drops to its original low value, which allows retracting springs on wheel brakes to pull the brake shoes out of contact with the brake drums into their original positions. This causes the wheel cylinder pistons to come back in their original inward position. Thus, the braking mechanism is complete.

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What are applications of Hydraulic brakes?

We use hydraulic brakes mostly in cars or automobiles. This is the most important application in the usage of hydraulic brakes. They can be seen in almost any car.


Here is a list of some most important advantages of hydraulic brakes.

  1. They transmit uniform pressure. (Due to hydrostatic pressure being equal in all directions, Pascal law).
  2. They help in multiplying the driver’s effort more times than that of Mechanical Brakes. (Hydraulic leverage ratio, hydraulic advantage). Higher mechanical advantage.
  3. The brake fluid also acts as a lubricant and reduce the frictional losses at high-speed braking.
  4. They are simpler in construction and lighter in weight.
  5. Thermal stresses generated are much lower in hydraulic brakes than Mechanical Brakes.
  6. However, they are more wear resistant. Hence, improving the advantages of hydraulic brakes.


  1. There is always a possibility of oil/fluid leakage which can render the system inoperative or compromise the friction surfaces.
  2. Extreme heat may cause the fluid to boil forming gas bubbles which compress and can’t transmit pressure effectively.
  3. However, Environmental factors such as moisture can deteriorate the hydraulic fluid over time and cause corrosion/failure of internal components.

Also see Drum Brakes, Disc Brake, and their working principles.

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