Classic car brake systems come in various forms and components. In restoring or even maintaining your classic which brake master cylinder types do you want to use and why. Do you go with factory original, mild modification, or major change to the heart of your brake system?
We often talk about the components and forces that help the vehicle to speed up or to perform. But have you ever thought about the amount of force required to stop the vehicle at such a high speed? Now this question gives rise to many other questions like from where does this high force generated? Which component is responsible for this high stopping force? Let us just discuss about the component responsible for generating this high brake force i.e., Master Cylinder. Hydraulic systems are comprised of three basic parts: a master cylinder (piston) that pushes fluid through the lines, the lines that carry the fluid and a slave cylinder that moves when fluid pressure pushes upon it. Modern “tandem” master cylinders utilize a pair of pistons in the same tube that control two different fluid circuits for redundancy that no single-piston design can offer.
Master cylinder in a classic car braking system is a hydraulic device in which cylinder and one or two pistons are arranged in such a manner that the mechanical force applied by the driver of a vehicle either by brake pedal (in cars) or by brake lever (in bikes) is converted into hydraulic pressure which in turn transferred to the brake caliper for braking. In hydraulic braking system, master cylinder is a device that provides required amount of pressure or braking force to the final braking components after multiplication of the mechanical force applied by the driver through brake pedal or brake lever.
Why We Need a Master Cylinder
As we all know now that a master cylinder in hydraulic braking system is an intermediate component that worked as an energy converter as well as force multiplier i.e., mechanical energy into hydraulic pressure so we need master cylinder in hydraulic braking system because-
- When we talk about today’s automobile vehicles due to their high speed, the brake force required (to stop or de-accelerate vehicle efficiently) is also high, which cannot be efficiently fulfilled by mechanical braking, so hydraulic braking with master cylinder is the new need of today’s vehicle as it generates higher brake force.
- As we all know that the brake force required in front wheels is higher than that of real wheels due to the shifting of mass from rear to front during braking, this distribution of brake force between rear and front wheels is a function of master cylinder.
- In hydraulic braking, the force applied by driver on brake pedal (in car) or brake lever (in bikes) during braking (50N-70N) is not enough to cause actual braking, so an intermediate component i.e., master cylinder is required that can multiply this force and further transfer this high force to the brake caliper which in turn generates high brake force and finally actual braking happens.
- In hydraulic braking the brake pedal or lever effort required for braking is drastically decreased due to the use of master cylinder as it acts as a converter that can convert the mechanical force applied by driver on brake pedal or lever into the high hydraulic pressure.
- The use of master cylinder decreases the chances of brake failure as it provides the constructional flexibility in which the braking in front and rear tire can be made independent of each other.
Brake Master Cylinder Types
Based on its construction and application brake master cylinders are of 2 types that are:
- Single Circuit Master Cylinder
- It is the simple type of master cylinder just like a medical syringe, in this type of master cylinder single piston inside a cylinder is used to cause braking.
- Single circuit m c (master cylinder) distributes equal force in all the wheels due to the use of single cylinder single piston or circuit.
- This type of master cylinder is commonly used in many 2 wheelers and some light weight 4 wheelers.
- Tandem Master Cylinder or Dual Circuit Master Cylinder
- It is the modified type of master cylinder in which dual cylinder-dual piston or single cylinder dual piston along with dual circuit is used for independent braking between front and rear wheels.
- This type of master cylinder is used in almost all cars as it is more efficient than single circuit master cylinder c.
- It provides the independency between front and rear wheels braking or diagonal type of braking which is the important safety feature for a vehicle.
Components
Single Circuit Master Cylinder
Single cylinders are the most basic type of master cylinder and are internally remarkably like a plastic medical syringe. The brake pedal lever pushes the plunger (piston) inside the cylinder, which shoves fluid through the lines and into the slave cylinders. When the brake pedal is released, a spring inside of the cylinder pushes the plunger back to its original position. Negative pressure pulls the brake fluid into the cylinder from the lines and from the brake fluid reservoir. Automakers long ago switched to the more redundant tandem master cylinder, but many race car builders prefer to use a pair of single cylinders instead of a single tandem cylinder to control front/rear brake pressure bias.
It consists of 5 parts:
- Reservoir
It is the storage tank used for storing the brake fluid in hydraulic type of braking system, usually it is made up of plastic.
- Cylinder
It is the airtight housing inside which the piston moves with the moment of brake pedal which in turn causes conversion and multiplication of force. Cylinder is usually made up of cast iron or aluminum.
- It relates to the reservoir through inlet valve and with brake lines through outlet valve.
- In single circuit m c, there is only 1 compression chamber.
- Piston
It is the reciprocating part of the master cylinder that reciprocates inside the cylinder due to the movement of brake pedal, the piston causes compression of brake fluid inside the cylinder which in turn generates high hydraulic pressure.
- In single circuit only 1 piston is used.
- Returning Spring
It is the simple coil type of spring used inside the cylinder which helps the piston and brake pedal to retain its original position after brake pedal is released.
- Valve
In single circuit master cylinder, it is the outlet valve through which the brake line is attached, the compressed brake fluid is further transferred to the caliper through this valve.
Tandem Master Cylinder
A tandem cylinder is two pistons in one. The primary piston is connected to the brake pedal. When the brake pedal is pressed, the piston pushes on a spring connected to the back of the secondary piston. Once that spring compresses fully, the secondary piston starts to push fluid through its own dedicated system. The reservoir inlet port allows fluid to flow behind the pistons to keep pressure even on both sides. When the brake pedal is released, spring pressure pushes the pistons back and a small compensating port from the brake fluid reservoir introduces extra fluid into the chamber. The compensating port is necessary to speed up brake release, which would otherwise be inhibited by the speed of the fluid moving backward through the lines.
1. Reservoir
In tandem master cylinder instead of single reservoir 2 or dual chamber reservoir is used as a storage tank for brake fluid.
- Cylinder
Same cylinder as in single circuit type is used with the little modification i.e., it is the housing of 2 pistons and there are 2 outlet and 2 inlet valves.
- In tandem master cylinder there are 2 compression chambers inside the cylinder.
- Piston
Instead of one piston, 2 pistons that are primary piston and secondary piston are used in tandem master cylinder, the actuation of secondary piston occurs after completion of the primary piston movement.
- primary piston is connected to the brake pedal and secondary piston is placed just behind the returning spring of primary piston.
- Returning Spring
In tandem master cylinder 2 returning springs are used one with the primary piston and second with the secondary piston.
- Valves
In tandem master cylinder as it is the dual circuit master cylinder, 2 inlet and 2 outlet valves are used.
Working
Single Circuit Master Cylinder
- In single circuit master cylinder when brake pedal is not pressed i.e., non actuation position the piston remains at its original position which in turn closes the inlet valve of the reservoir due to which there is no incoming of brake fluid takes place between reservoir to compression chamber.
- When brake pedal is pressed i.e., actuated position, the piston which is connected to the brake pedal through connecting rod moves which in turn opens the inlet valve due to which incoming of brake fluid from reservoir to compression chamber takes place.
- This brake fluid inside the compression chamber is compressed due to the movement of piston inside the cylinder just like the medical syringe.
- After compression up to a certain pressure the outlet valve opens, and this highly compressed brake fluid is further transferred to the brake lines for further brake actuation.
Tandem Master Cylinder
The working of tandem master cylinder is 70% same as the single circuit master cylinder, but in this type 2 independent circuits of braking is used. Let us see how it works:
- When brake pedal is not actuated, the piston remains at their original place, closing the inlet valve of both the compression chambers, which in turn cuts the incoming of brake fluid between both the reservoir and both the reservoir chambers.
- When the brake pedal is actuated, at first the primary piston moves due to which opening of primary inlet valve takes place.
- Initially due to the movement of primary piston compression of the brake fluid inside primary chamber takes place.
- After completion of the compression in primary chamber primary outlet valve opens and this compressed brake fluid is further sent to brake calipers through brake lines and actuation of the primary circuit brakes take place.
- After the completion of the primary piston movement i.e., at its extreme end, the secondary piston starts moving because of the force applied by the primary piston’s spring which in turn opens the secondary valve and incoming of brake fluid from secondary reservoir to secondary compression chamber takes place.
- This brake fluid is then compressed and after complete compression secondary outlet opens and this highly compressed fluid is sent to the brake calipers through brake lines and actuation of the secondary circuit brakes take place.
Single Circuit Master Cylinder
- It is mainly used in 2 wheelers like Bajaj pulsar, TVS apache etc.
- Many lightweight vehicles like e-rikshaws are also using this type of master cylinder.
Tandem Master Cylinder
- It is widely used in almost all the cars equipped with hydraulic braking system.
- Using tandem master cylinder in vehicle equipped with hydraulic braking system is made compulsory by governments of many countries because of its safety to brake failure.
The brake master cylinder is a critical component to your vehicle’s braking system. Understanding the role of the brake master cylinder can help you determine if you want to replace it and what to look for in a replacement. In Part 2 let us take a brief overview of a braking system, then get into detail about the role of the master cylinder. We will look at single and dual reservoir cylinders, bore size, and all the components of the master to help you make the best choice for your classic car.
