Master Cylinder:
In automotive technology, the brake cylinder is a control device that converts force (commonly from a driver’s foot) into hydraulic pressure. This device controls slave cylinders located at the opposite end of the mechanism.
As piston(s) move along the bore of the hydraulic brake cylinder, this movement is transferred through the hydraulic fluid, to lead to a movement of the slave cylinder(s). The hydraulic pressure created by moving a piston (inside the bore of the master cylinder) toward the slave cylinder(s) compresses the fluid evenly. But by varying the comparative expanse of the brake cylinder and every slave cylinder. One can vary the number of force and displacement applied to every slave cylinder, relative to the quantity of force and displacement applied to the brake cylinder.
hydraulic pressure
The hydraulic brake cylinder is found behind the driver’s side dashboard mounted on the vacuum booster. The pressure inside the piston chamber is made by a primary and secondary piston. These are pushed by the output rod of the vacuum booster to compress fluid within its primary and secondary chambers (hydraulic pressure). The hydraulic pressure is translated through the brake lines to the brake calipers. When the brake fluid is pushed through the brake lines, the piston chamber chambers are replenished by the reservoir (attached to the highest of the master cylinder).
For hydraulic brakes or clutches alike, flexible high-pressure hoses or inflexible hard-walled metal tubing is used; but the flexible style of tubing is required for a minimum of a brief length adjacent to every wheel, whenever the wheel can move relative to the car’s chassis (this is that the case on any car with steering and other suspension movements; some drag racers and go-karts haven’t any rear suspension).

How Do Master Cylinders Work?
Most master cylinders have a “tandem” design (sometimes called a dual master cylinder).
In the tandem master cylinder, two master cylinders are combined inside a single housing, sharing a common cylinder bore. This allows the cylinder assembly to control two separate hydraulic circuits.
Each of these circuits controls the brakes for a pair of wheels.
The circuit configuration can be:
- Front/rear (two front and two rear)
- Diagonal (left-front/right-rear and right-front/left-rear)
This way, if one brake circuit fails, the other circuit (that controls the other pair) can stop the vehicle.
There’s also a proportioning valve in most vehicles, connecting the master cylinder to the rest of the brake system. It controls the pressure distribution between the front and rear brake for balanced, reliable braking performance.
The master cylinder reservoir is located on top of the master cylinder. It must be adequately filled with brake fluid to prevent air from entering the brake system.
Here’s what happens in the master cylinder when you press down on the brake pedal:
- A pushrod drives the primary piston to compress the brake fluid in its circuit
- As the primary piston moves, hydraulic pressure builds inside the cylinder and brake lines
- This pressure drives the secondary piston to compress the brake fluid in its circuit
- Brake fluid moves through the brake lines, engaging the braking mechanism
When you release the brake pedal, the springs return each piston to its initial point.
This relieves the pressure in the system and disengages the brakes.

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