LEARN ABOUT BRAKES

A vital part of your vehicle that you definitely don’t want to take for granted.

Pascal’s Law

By unknown; a copy of the painting of François II Quesnel, which was made for Gérard Edelinck en 1691[réf. nécessaire]. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=12193020 — By unknown; a copy of the painting of François II Quesnel, which was made for Gérard Edelinck en 1691[réf. nécessaire]. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=12193020

Blaise Pascal stated that pressure exerted on a fluid in an enclosed container is transmitted equally and undiminished to all parts of the container and acts at a right angle to the enclosing walls.

A common example of his work is shown by the use of a u-tube. With fluid in it and a piston of equal size on each side, if Piston A were to move, Piston B would move the same with the same amount of force.

Pascal’s Law Put To Work

A more practical use of this law comes into play when using pistons of a different size. If a smaller piston is being moved like the image below, a larger piston will move less distance but with a greater force.

HYDRAULIC

“operated by a liquid moving in a confined space under pressure”

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LEVERAGE

“the exertion of force by means of a lever or an object used in the manner of a lever”

HYDRAULIC LEVERAGE

The force applied at one point is transmitted to another point using an incompressible fluid. Almost always an oil of some sort. Most brake systems also multiply the force in the process.

Introduction to Brakes

Whenever an object is put into motion, kinetic energy is being produced. The brakes are used to stop this motion by removing the kinetic energy which is done by converting it to heat through the use of friction.

In physics, the kinetic energy (KE) of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes.

If for example you were riding your bicycle, there are a few different ways you could stop. You could hit a tree, drag your feet or squeeze the brakes.

The first way works great if you want to stop fast. The downside is that your only going to do it once and you may get an injury from it.

The second way by dragging your feet, not as much damage would occur besides scuffing your shoes but also it may take awhile to get you to stop.

With the incorporation of brakes, mechanical and / or hydraulic leverage can be used to supply sufficient stopping power.

Automotive Braking System

A lot more friction is going to be needed when it comes to trying to stop a moving vehicle and the pressure from your foot alone wouldn’t be possible without taking advantage of mechanical and hydraulic leverage. As you can see in the first image, the brake pedal is on a pivot giving the operator more leverage to push against the master cylinder pushrod. You will also notice by looking at the second cylinder that there are two pistons within the master cylinder. These pistons are much smaller than the ones found in your brakes.

What does all this mechanical and hydraulic leverage allocate to?

The ability to put a tremendous amount of force on the brakes.

Another thing worth noting is that since the brake fluid is contained in a sealed environment, there should be no reason for the fluid to escape. It is still possible though for the fluid level to drop in the reservoir. Why do you think this happens?

As your brakes wear down, the pistons in the calipers and drums are extruding more causing less fluid to return to the reservoir after release. With this in mind, if you see your fluid is low and there is no obvious leaks or drips, check your brakes.

Two of the main types of braking systems seen on vehicles today are disk brakes and drum brakes. The system can have either one style or a combination of the two. Disc brakes on the front and drum brakes on the rear being the most common.

Looking at the designs, what advantages can you see with one vs. the other?

Disc Brakes

The disc brake system operates by squeezing brake pads against a rotor. The brake pads are attached to the brake calliper which is mounted to the vehicle and the rotor spins with the wheel. When the operator pushes the brake pedal down, mechanical leverage is converted to hydraulic by the master cylinder. The additional pressure in the system causes the pistons to press the brake pads against the rotor creating friction, stopping the vehicles motion as a result.

Potential Issues

Seized brake piston or slider pins
Worn out or warped brake rotors

Disc Brake Advantages

Higher performance braking
Less moving parts
Better resistance to water than a brake drum setup
All components are open to air flow

Calliper Components

Piston Seal prevents fluid leakage between the piston and the cylinder and helps pull the piston back into the cylinder when the brakes are not applied.

Dust Boot prevents road dirt and water entry on the caliper piston.

Bleeder Screw allows air to be removed from the system for repair or servicing.

Brake Pads are steel plates to which linings are riveted or bonded.

Brake Pad Material is made of heat resistant organic, semi-metallic, metallic or ceramic friction material. Semi-metallic linings withstand higher temperatures without losing their frictional properties. Ceramic brake pads are more expensive and last longer.

Brake Pad Selection: organic or semi metallic brake pads are commonly used in conventional passenger car applications, metallic pads are used on performance vehicles (Police, ambulance, taxi and sports cars.)

Anti Rattle Clips keep the brake pads from vibrating and rattling.

Pad Wear Sensors are metal tabs on the brake pad that emit a loud squeal when it scrapes against the brake disc when the lining has worn too thin.

Anti Squeal Compound keeps the brake pads from squealing, the compound is puasft on the contact surfaces of the pad and creates a gasket between the metal components

Brake Rotors use friction from the brake pads to slow or stop wheel rotation. Normally made of cast iron, constructed as part of the hub or a separate unit and can be solid or a ventilated rib construction.

Drum Brakes

A drum brake works somewhat opposite of a disc brake system. Instead of brake pads squeezing a rotor, brake shoes are forced outwards against a cast iron drum within which it is contained. Lets take a look at the following slide to see how they work.

Brake Fluid

In order for a hydraulic brake system to work properly a special fluid must be used which surprisingly enough is called brake fluid. There are a few different types available, each with it’s own properties. The one you use depends on manufacturer specifications and can very from vehicle to vehicle.

Desired Brake Fluid Characteristics

Correct viscosity at all temperatures
High boiling point
Non Corrosive
Water tolerant
Lubricates components
Low freezing point

Why are these characteristics so important?

DOT 3

Commonly found in domestic cars & Trucks, DOT 3 brake fluid is alcohol based and can absorb 2 percent of its volume in water every year. Over a long period of time, moisture can cause corrosion in the brake system leading to vapor-lock or a spongy brake pedal. You must also be mindful of spilling it on paint.

DOT 4

Like DOT 3, it’s an alcohol base and is made for use by all vehicles. The difference between the two would be that the DOT 4 has a higher boiling point and it does not absorb moisture as fast. You can interchange the two fluids although it is not recommended. Most commonly found in high performance vehicles that demand a lot from their brakes.

DOT 5

Unlike the previous fluids, DOT 5 is silicone-based. For this reason it does not absorb any moisture and has the possibility of expanding more when compressed which can make the pedal feel spongy. A positive to this type of fluid is that since it doesn’t contain alcohol, it’s not corrosive to paint or brake components.