Lesson 7: Brakes & Suspension Systems

                                                                                               

                                                 

Welcome to the brakes and suspension systems lesson. In this lesson

we will cover:

o Brakeso How your brakes worko What maintenance is required?o Checking brake fluido Checking brake pads

o How to know if your brakes are worn outo Learn to recognize symptoms and causes of common brake

problemso What are anti-lock braking systems?

o Suspension Systemso What is the suspension system?o Springso Shock absorbers

o How to know if something is wrong with the suspension system

BrakesA lot of emphasis is placed on how fast a car can go from zero to sixty miles per hour, but many people don’t even consider how long it might take them to go from sixty back to zero.

The braking system is perhaps the most important system on any automobile—and making sure that it works properly may be one of the most important decisions you ever make!

How your brakes stop your car: When you press your brake pedal,

you are actually pushing on a piston inside of a master cylinder.

This piston pushes brake fluid through brake lines and hoses to each wheel, where the pressure is used to apply the brakes and stop the car.

At each wheel, there is one of two types of brakes: Disc Brakes or Drum Brakes. Each of these types of brakes will be discussed in the next two slides.

Piston

Did you know? The front brakes on your car do 60%-80% of the braking! Because of the momentum and weight transfer that occurs during braking, a whole lot more is expected of your front brakes than of your back brakes.

Because disc brakes are more efficient than drum brakes, all modern cars have disc brakes on the front wheels (where most of the braking takes place), while the back brakes can be either type, depending on the car.

To slow or stop the wheel from turning, brake fluid forces a piston to clamp the brake pads against the rotor. The harder you press on your brake pedal, the harder the brake pads clamp against the rotor. This clamping causes friction, which slows the rotor and wheel down, eventually stopping it completely.

Disc Brakes

Brake fluid

As just mentioned, all modern cars use disc brakes on the front wheels. Disc brakes have a disc or “rotor” just inside the wheel. It turns when the wheel turns.

RotorCaliper (has piston and brake pads in it)

Wheel Stud (lug nuts go here)

Rotor

Brake Pads

Drum BrakesThough they are becoming less common, drum brakes are still found on the rear wheels of most cars on the road today. Drum brakes have a “drum” that sits just on the inside of the wheel and rotates with the wheel.

When you apply your brakes, the brake fluid pressure causes the pistons in the wheel cylinder to push the brake shoes out, against the inside of the rotating drum. The friction caused as the brake shoes push against the drum slows the drum and the wheel.

Click here to see an animation showing how drum brakes work

Wheel cylinder

Drum

Brake Shoes

Drum Brake Shoe

Parking BrakesAll cars have a parking brake—a separate braking system operated by a cable rather than by hydraulics. In most cars, when you pull the parking brake lever or push the parking brake pedal, it pulls a cable which applies the drum brakes on the rear wheels.

Parking Brake being applied

Parking brake leverThe most common cause of parking brake problems is forgetting to take the brake off before driving. This wears the brake shoes out quickly.

If your parking brake doesn’t work well enough to hold the car from rolling on a hill, have it checked. If the brake shoes are in good shape and are adjusted properly, the parking brake cable may need to be tightened.

Return to I-learn now and watch the video entitled “Brakes Basics.”

What needs to be checked?Basically, the braking system is designed to work without a lot of trouble. The only maintenance you should have to perform is to have your brake pads or brake shoes changed when they wear out. However, a conscientious car owner will keep an eye on things, spotting problems before they become dangerous.

It is strongly suggested that you regularly check:

o Your brake fluido Your brake pads and/or brake shoeso For new or unusual noises or vibrations

(each of these will be discussed next)

Check your brake fluidWhen you are under your hood checking your other fluids, why not check your brake fluid, too?

To check your brake fluid level, locate your brake fluid reservoir and look at the marks on the side. The fluid should be somewhere between the “min” and the “max” marks.

As your brake pads and brake shoes wear thinner, more of your brake fluid travels into the lines and to the brakes, where it takes up the space that used to be occupied by the thicker brake pads or shoes. This makes the fluid level in the reservoir appear lower.

Your braking system does not use up fluid, so if the level is low, it is either because the brakes are wearing out or there is a leak in the system.

As a rule of thumb: Keep the fluid level above the “min” mark, but otherwise, don’t add fluid. If the fluid level is near the “min” mark, have your brakes checked!

When Should you add fluid?

MIN

MAX

The brake fluid reservoir is connected to the master cylinder—which is usually

under the hood on the driver’s side of the car (it

is directly through the firewall from where the brake pedal is located).

What type of brake fluid should you use?

As with other fluids, only use the type of brake fluid that your car calls for!

Most cars call for DOT 3 brake fluid, but a few require DOT 4 fluid.

You can usually find this information on the cap of your brake fluid reservoir. But if not, check in your owner’s manual.

• If you spill it on a painted surface and don’t clean it up immediately, the paint will peel off!

• It can be cleaned up with water.

• It absorbs moisture—even from the air—so never use brake fluid from a container that has been opened for very long!

Here are some interesting facts about brake fluid:

Brake pads & brake shoesBrake pads (disc brakes) and brake shoes (drum brakes) consist of a backing plate and friction material. As brakes get used, the friction material wears away. Checking your brakes basically means checking to see how much friction material is left.

You should have your brakes checked each time you have your tires rotated. It is recommended that you do this every 6,000 miles or at every other oil change.

Brake Pads (disc brakes)

Brake Shoes (drum brakes)

Friction Material

Backing Plate

Checking pads & shoesIf you choose to check your own brakes rather than have a professional do it, here is what you should know:

You should remove each wheel from your car and locate the brakes. Look at the thickness of the friction material on each brake pad and/or brake shoe. If any part of the material is as thin or thinner than a nickel, the brakes should be serviced and changed.

If the friction material is thicker than this, you may still have some wear left. Remember that at each wheel there are two pads or two shoes; check them both!

New Brake Pad

No Friction Material Left NOT USABLE

To check brake pads, you can usually look through the caliper and see the pads once the wheel is off.

Rotor

Backing Plate

Friction Material

What’s that noise?We’ve all heard squeaky brakes before. Is that something to

worry about? The answer to that question is, “it depends.” If the brakes only squeak when you apply the brakes to stop, it is probably nothing to worry about. This is often caused by brake dust or cheap brake pads.

However, if you experience a “squeaking” or “scraping” sound that occurs when the brakes are not applied and either disappears or changes slightly when the brakes are applied, this is the sound of a “wear indicator.” This means that your brake pads are worn out!

Backing plate

Wear Indicator

Or ‘Squeaker’

Friction material

Most brake pads are equipped with a wear indicator—a small

metal clip that will start to scrape on the rotor when the friction

material is worn down. When you hear this noise it is time to

change the pads!

Rotor Wear Indicator

Friction Material

Other brake problems you may experienceSymptom Cause FixBrake pedal pulsates (or steering wheel vibrates) when stopping--especially from highway speeds

Brake rotors are warped-- caused by overheating brakes

or using power tools to tighten lug nuts

Rotors must be resurfaced or replaced

Rough, grinding noise while braking

Brake pads or shoes are beyond worn out--the friction material is completely gone

and the metal backing plate is rubbing on the rotor or drum

Service brakes immediately, replace pads, drums and/or

rotors

Brake pedal sinks farther than it should; car doesn't stop well

Drum brakes adjusted incorrectly, air in the brake

lines, brake fluid leakHave the braking system

checked immediately!

When stopping on ice or snow, brake pedal buzzes and pushes

back at your foot

The anti-lock brakes are working normally to help

prevent the car from sliding out of control

No repair necessary; this is normal

Tips for those who choose to service their own

brakes:• Don’t use the “cheap” brake pads. They wear out fast and are often noisy! Rather, buy “original equipment” or better pads.

• Don’t get grease or fingerprints on brakes pads, shoes, rotors, or drums.

• Clean and lubricate caliper sliders with special brake grease (not ordinary grease).

• Make sure all clips, shims, and retainers are installed correctly.

• Tighten wheel lug nuts evenly and by hand (no power tools).

Whether you choose to service your own brakes or to have it done professionally, just make sure that it is done before the pads or shoes are completely worn out. If you wait too long, the cost of the repair will increase.

Also, make sure that the brake service is done correctly—your life may depend on it!

Optional: Return to I-learn and watch the video entitled, “Checking Brakes.”

Putting the whole braking system together:

What is ABS?Antilock Braking Systems (ABS) are designed to help you maintain control of your car when you are braking. Basically, the brakes on vehicles with ABS work just like any other car. However, the car has a sensor at each wheel that is constantly monitoring for a skidding wheel.

If, while you are braking, one or more of the wheels loses traction and breaks free from the road, the ABS system begins “pumping” the brakes in order to help the tires regain traction.

An ABS system may or may not help you stop faster, but what it will do is help you to be able

to steer and control your car while you are braking. Without ABS, skidding usually means

a loss of control—and often an accident.

Return to I-learn now and watch the video entitled “ABS.”

Question: If I have a car with antilock brakes, should I still pump the pedal when I am stopping on ice?

Answer: No. The ABS system does it for you. Just apply the brakes like you would on dry pavement.

The components of an ABS-equipped vehicle:

Dash warning lights:

Your brake warning light on your dash will come on for any one of the following reasons:

If you have anti-lock brakes, your ABS warning light on your dash will come on if there is a malfunction in your ABS system. Here’s what it means:1. The parking brake is

applied2. Brake fluid is too low in the

reservoir3. There is a problem with

the hydraulic system that applies your brakes

If this light is on, the ABS system will be disabled. However, your regular brakes will continue to work—so don’t panic, just get checked out soon.If your brake warning light

comes on, figure out why and get it fixed immediately; your

safety could be at risk!

Here’s some “braking” news:When driving down a steep hill, we often have to use our brakes a lot to keep the car from gaining too much speed. However, this has some serious implications.

If you apply the brakes too much, a lot of heat builds up in the brake pads and rotors. In fact, it can burn the brake pads, warp the rotors, and worst of all—it can cause the brake fluid to boil, resulting in NO BRAKES!

There are a couple of things every driver should know about driving down hills:

1. Don’t ride your brakes! Go slowly and apply your brakes as little as possible, allowing them to rest and cool down between applications (you should never brake more than about 20% of the time).

2. Shift to a lower gear. If you have an automatic transmission, you can shift into the gear just past “Drive.” This will allow the engine to help slow you down.

3. If you smell burning brakes, pull over immediately and let them cool off.

Suspension SystemsTo help us understand the suspension system, we can separate the car into two parts:

1. The tires, wheels and brakes that sit on the ground (unsprung) 2. The body and the rest of the car that rests on springs (sprung)

Sprung

Unsprung

Why do I need a suspension system?

1. Obviously, it helps to smooth out the ride. The springs allow the wheels to move up and down in response to bumps or dips in the road with minimal movement of the car itself.

2. It also helps to keep the wheels on the road. The car is much safer if all four wheels maintain contact with the road! As the car maneuvers around corners and over bumps, the suspension system allows the wheels to move independently of the rest of the car.

The suspension system does two things for you and your car:

When cornering, the suspension system helps to keep the wheels

on the road.

The suspension system

responds with agility to bumps

or dips in the road.

A bit of history:Early cars and horse-drawn wagons did not have suspension systems.

This is a photograph of Henry Ford and his first car. Without a suspension system, he probably felt every pebble in the road!

Shock absorbers

Besides springs, suspension systems also have shock absorbers. Shock absorbers are usually near the spring and compress and rebound whenever the spring does.

Without a shock absorber, the springs would make the vehicle very bouncy. In fact, after hitting a bump, the vehicle would probably bob up and down for quite a while before finally coming to a rest.

The shock absorber “absorbs” the spring oscillations, so that the car stops bouncing after only 1-2 bounces.

Many people are confused about the role of the shock absorbers. Shock absorbers do not support the weight of the vehicle—the springs do that. Shock absorbers simply

reduce the “bounciness” of the springs.

Spring

Shock absorber

What is a strut?Essentially, a “strut” performs the same function as the shock absorber. The only difference is that the strut also plays a role in supporting the vehicle. Struts are commonly found on front-wheel-drive cars. Because they are so similar, for our purposes, it is fine to lump shocks and struts into the same category.

Strut

The shock absorber is inside the strut and, often,

the spring surrounds it.

Return to I-learn now and watch the video entitled, “Suspension Systems.”

Checking Shock absorbers and struts

Return to I-learn now and watch the video entitled “Checking Shocks.”

As car owner, you can check your own shock absorbers

and struts. It is simple, easy, and kind of fun. However,

your neighbors may wonder what you are doing!

• Visual Inspection: Look at the shock or strut for physical damage or leaking oil. If it is leaking oil, it should be replaced.

• The Bounce Test: Bounce each corner of the car, then let go. If the car bounces more than twice before it comes to a rest, the shocks or struts should be replaced.

Shock absorbers and struts should be replaced in pairs. For example, if the right front shock is faulty, both front shocks should be replaced.

ConclusionGood, predictable stopping and vehicle handling is part of safe

driving. In this unit we explored how the braking system and suspension system work to help make an automobile comfortable and safe.

We learned how to identify common problems in these systems, as well as how to perform routine inspections and maintenance that will save money and prolong the life of your automobile.