In the following sections, we will examine the necessary systems and components that make the brakes work effectively.
After completing this material, students are expected to understand and be able to apply their knowledge of:
1. Brake function and components
2. Drum brake
3. Disc brake
4. Hydraulic system
5. Master cylinder
6. Pressure control system
7. Brake fluid
8. Brake power boost system
9. Basic Diagnosis
10. Service brakes
Vehicle brakes are designed to slow and stop the vehicle by converting kinetic energy (energy of motion) into heat energy.
The brake pad presses the drum/disc, causing friction which generates heat energy. The heat intensity is proportional to the weight and speed of the vehicle.
1. The Principle of Friction.
Friction is resistance to movement resulting from two objects moving or rubbing against each other. There are two types of friction: kinetic and static. Kinetic friction occurs between two objects, one of which is in motion. Kinetic friction always generates heat. The more kinetic friction that is generated, the more heat is generated. The vehicle's braking system uses kinetic friction to convert the energy from a moving vehicle into heat.
Static friction occurs between two objects at rest. The vehicle braking system uses static friction to hold the vehicle while it is parked. Static friction does not generate heat.
Various factors influence the resulting friction between two objects, including:
a. Surface roughness of two objects.
The rougher the surface of an object the more friction it creates. A very rough surface creates a large amount of friction, but a rough surface also causes the friction surface to wear out quickly. Therefore, vehicle brakes use a relatively smooth surface to avoid the friction surface from wearing out quickly. Therefore to compensate for the smooth surface, the vehicle brakes
use with an amount of pressure over a relatively large frictional contact area.
b. Pressure
The greater the pressure on an object, the more friction it produces. Therefore, the more pressure applied to the brakes, all other factors being equal, the more brake power is generated.
c. Number of swipe fields.
The greater the number of areas of common contact between two objects, the greater the amount of friction produced.
The vehicle's braking system uses the largest possible contact area. The larger the contact area of the brake shoe or pad, the less heat generated on the brake shoe or pad. Less heat allows more efficient brakes.
2. Heat and brake linings.
The friction surface of the brake lining is very important, the brake lining produces direct friction on other friction surfaces, whether drum or disc brakes. Brake pads and brake friction materials must have special characteristics, including:
* Drum or disc brakes should be able to dissipate heat easily.
* Holds its shape under very high heat.
* Withstand rapid temperature changes, resist bending and distortion.
Therefore, drums and discs are usually made of iron or steel combined with aluminum. The brake pads should be softer than
drum or disc. Meanwhile, brake pads are made of organic materials, metal particles, and other minerals into one unit.
Note: For many years, asbestos has been commonly used in brake pads. Asbestos is a compound that causes cancer.
* If the friction coefficient is too large, the brakes are too sensitive, which can cause the vehicle to slip easily.
* If the coefficient of friction is too low, the brakes require excessive pressure. Excessive pressure brakes create excessive heat which can result in brake system failure.
3. Weight and Speed.
The heavier the moving vehicle, the more kinetic energy it has. The brake system must convert kinetic energy into heat, so that every increase in vehicle weight the greater the demand for brake force. Therefore, the brakes on overloaded vehicles become ineffective due to overheating. As the vehicle speed increases, the brakes must convert four times the amount of kinetic energy into heat. The speed is greatly increased the demand for brake force has also increased. The combination of excessive speed and weight can cause the vehicle's brakes to exceed the brake performance limits, resulting in a serious loss of braking power.
4. Friction between tires and road
The point where the tires of the vehicle come into contact with the road are called the tire tracks. Changes in tire tracks affect the vehicle's ability to stop. The following are the factors that affect tire tracks.
a. The larger the tire diameter, the bigger the tread. As a general rule, that the larger the diameter of the tires, the greater the brake the force required and the wider the tires, and the more braking force required to stop the vehicle.
b. Excessive vehicle weight can distort the tread and thus reduce tire grip on the road. Tires that cannot hold the road can reduce the vehicle's ability to stop. High vehicle speed can also cause the vehicle to lift due to aerodynamic factors. Lifting reduces tire grip on the road and reduces the vehicle's ability to stop.
c. To control the vehicle, the grip must remain on the tire tread. If this is lost, the vehicle gets out of control .. Therefore, the braking force will be reduced if the brakes lock the wheels (block) .. If the brake system locks the wheels too easily, it significantly reduces the braking force and control of the vehicle.
C. Drum brake.
A drum brake unit consists of two brake shoes attached to a backing plate. When the brake pedal is depressed, the hydraulic wheel cylinder will push the shoe out to suppress the rotating drum and cause friction, thus slowing the vehicle.
When the pedal is released, the return spring pulls the brake shoes back to their original position.
1. Drum brake components.
In general, the drum brake components include:
1. Drum brake. (drum)
2. Brake shoe with friction linings. (brake shoe)
3. Wheel cylinder. (wheel cylinder)
4. Anchors.
5. Backing plate.
6. Springs (Spring brake shoes).
7. Return springs.
8. Adjuster (adjusting unit).
a. Drum
The drum rotates together with the wheel. In some brake systems, the drum is the wheel hub and wheel bearing. The drum must be perfectly round and concentric with the shaft. The brake pedal will vibrate if the drum is not perfectly round or nonconcentric with the spindle or shaft. Grooves on the inner surface of the drum (friction plane) will be formed because of friction, grooved drum increases the friction coefficient is reduced. The drum must also be able to absorb and dissipate the amount of heat that arises from friction.
* Types of the drum.
External drum
Cast iron drum.
Aluminum drum.
* Drum wear marks.
The wear limit is usually located on the front of the drum. If the wear limit is exceeded, the drum will be too thin to absorb heat properly, and the braking force will be reduced. In addition, thin drum can warp, crack, or even crumble during braking.
Most brake drums are marked with dimensions that indicate the maximum turning limit. This limit is called the maximum diameter or exhaust diameter. This dimension is poured or printed when the drum is formed.
b. Brake shoe.
When the driver presses the brake pedal, hydraulic pressure from the wheel cylinders presses on the brake shoes, and the accelerator presses the brake drum, resulting in friction that converts kinetic energy to heat. The arc-shaped brake shoe conforms to the surface of the brake drum. Brake pads made of a special bonded (glued) or glued to the brake shoes.
c. Wheel cylinder. (Wheel cylinder)
The wheel cylinder consists of the following parts: 1. Cylinder 2. Pistons 3. Lip seal piston cups 4. Expander spring assembly 5. protective dust covers 6. Actuating pins (some models) 7. Bleeder valve
When the driver hits the brake pedal, hydraulic pressure from the master cylinder moves to the wheel cylinder. In a wheel cylinder, hydraulic pressure causes the piston seal to push the piston. The action of the cylinder's hydraulic pressure forces the brake shoe against the drum. When the driver releases the brake pedal from the stomp, this reduces hydraulic pressure. The brake shoe return spring then pulls the brake shoe back to its original position. The wheel cylinder is connected to the master cylinder by means of a series of steel pipes and a special high pressure rubber hose. The wheel cylinder is bolted to the brake backing plate. Each wheel cylinder has a drain valve that allows it to remove air from the wheel cylinder. There are three types of wheel cylinders, namely:
* Single piston wheel cylinder.
* Two piston wheel cylinders.
* Multilevel wheel cylinders.
d. Anchors.
The anchor is the part of the drum brake system attached to the backing plate that forms the support of the brake shoe. The anchor bears all the power of the drum brake shoe.
Some non-servo systems use two anchors per wheel, one for each brake shoe.
The brake shoe holding device is like a spring and a pin that holds the brake shoe against the backing plate. This allows the brake shoe to slide outward against the drum when the driver applies the brake.
e. Backing Plate.
Backing Plate is a steel disc that is attached to the axle housing and cannot rotate.
The backing plate is the foundation for the drum brake system, in which the anchor and wheel cylinder, brake shoe, return spring and some adjusters are attached to the backing plate. The Backing Plate is a pad on which the brake shoes can move.
f. Brake Shoe Springs.
Two main types of brake shoe holder springs are drum brakes. This spring holds the brake shoe against the backing plate, while at the same time allowing the brake shoe to move when the brake is operated.
* Coil Spring
The coil spring holder consists of a round pin, a spiral spring and a ring. One end of the pin is formed into a flat shape and the other end is flattened. These pins are installed through the holes in the backing plate and the holes in the brake shoe. The pin passes through the coil spring and the ring is installed through the brake shoe.
g. Brake shoe return spring.
The brake shoe return spring is always the coil spring type. A spring that is connected between the brake shoe and a stationary seat or from one brake shoe to another. The function of the brake shoe return spring is to return the brake shoe to a position where the wheel cylinder is not subjected to hydraulic pressure. When the hydraulic pressure of the wheel cylinder pushes the brake shoe to push the drum outside. At the same time, the springs are stretched due to movement of the brake shoes. When the brake pedal is released from stamping, the wheel cylinders lose hydraulic pressure. Thus, the spring pulls the brake shoes to their original position, and pushes the wheel cylinder pistons to the un-depressed position. Some drum brake assemblies have a return spring attachment attached between the two brake shoes for the purpose of helping to restore the brake shoe and also to maintain alignment between the shoe and the mount. Return springs are sometimes color-coded to indicate a change in model or to identify when to re-install.
h. Anti-Rattle Springs.
Anti-vibration springs used in drum brake assemblies are for reducing vibration and clicking sound. The trick is to provide a little spring tension between the two parts.
This tension takes the slack away from and keeps the pieces from clinging to one another. Most anti-vibrate springs are coil springs.
i. Adjustment unit
Almost all modern drum brakes use some form of adjuster in the form of a star wheel (toothed wheel). On many systems, the star wheel adjuster is located at the bottom of the brake shoe unit, with the wheel cylinder on top. In some drum brake systems, the adjuster, which is positioned at the top, directly under the wheel cylinder, with the bottom of the brake shoe retainer.
The star wheel design is called a floating adjuster, because it does not rest against the backing plate and can move along with the brake shoe.
The star wheel adjuster can be changed manually to adjust the clearance between the brake shoe and the drum. All-star wheels used in modern vehicles are operated by an automatic linkage adjuster.
An adjustment unit consists of three main parts: star wheel, pivot nut, and socket. Turning the star wheel causes it to thread in or out of the pivot nut. This makes the adjuster unit extend or retract, depending on which direction the star wheel is turned. The different threaded Star wheels for the left and right wheels are marked with the letter L or R. This indicates whether the adjuster should be installed on the left or right side of the vehicle.
Types of adjusting star wheel construction include:
a. Cable Adjusters.
b. Adjuster link.
c. Lever Adjuster.
d. Ratchet Adjusters.
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