08-10-2012, 04:51 PM
Automotive Brake System
Braking systems.PDF (Size: 215.8 KB / Downloads: 120)
The modern automotive brake system has been refined for over 100 years and has become extremely
dependable and efficient.
The typical brake system consists of Disk Brakes in front and either disk or Drum Brakes in the rear
connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder. Other
systems that are connected with the brake system include the parking brake, power brake booster and
the anti-lock system.
When you step on the brake pedal, you are actually pushing against a plunger in the master cylinder
which forces hydraulic oil (brake fluid) through a series of tubes and hoses to the braking unit at each
wheel. Since hydraulic fluid (or any fluid for that matter) cannot be compressed, pushing fluid through a
pipe is just like pushing a steel bar through a pipe. Unlike a steel bar, however, fluid can be directed
through many twists and turns on its way to its destination, arriving with the exact same motion and
pressure that it started with. It is very important that the fluid is pure liquid and that there are no air
bubbles in it. Air can compress, which causes a sponginess to the pedal and severely reduced braking
efficiency. If air is suspected, then the system must be bled to remove the air. There are "bleeder screws"
at each wheel cylinder and caliper for this purpose.
Master Cylinder
The master cylinder is located in the engine compartment on
the firewall, directly in front of the driver's seat. A typical master
cylinder is actually two completely separate master cylinders in
one housing, each handling two wheels. This way if one side
fails, you will still be able to stop the car. The brake warning
light on the dash will light if either side fails, alerting you to the
problem. Master cylinders have become very reliable and rarely
malfunction; however, the most common problem that they
experience is an internal leak.
This will cause the brake pedal to slowly sink to the floor when your foot applies steady pressure. Letting
go of the pedal and immediately stepping on it again brings the pedal back to normal height.
Brake Fluid
Brake fluid is a special oil that has specific properties. It is designed to withstand cold temperatures
without thickening as well as very high temperatures without boiling. (If the brake fluid should boil, it will
cause you to have a spongy pedal and the car will be hard to stop.) Brake fluid must meet standards that
are set by the Department of Transportation(DOT). The current standard is DOT-3 which has a boiling
point of 460º F. But check your owners manual to see what your vehicle manufacturer recommends.
The brake fluid reservoir is on top of the master cylinder. Most cars today have a transparent reservoir so
that you can see the level without opening the cover. The brake fluid level will drop slightly as the brake
pads wear. This is a normal condition and no cause for concern. If the level drops noticeably over a short
period of time or goes down to about two thirds full, have your brakes checked as soon as possible. Keep
the reservoir covered except for the amount of time you need to fill it and never leave a can of brake fluid
uncovered. Brake fluid must maintain a very high boiling point .Exposure to air will cause the fluid to
absorb moisture which will lower that boiling point.
Other Components in the Hydraulic System
• Proportioning valve or Equalizer Valve
These valves are mounted between the master cylinder and the rear wheels. They are designed
to adjust the pressure between the front and rear brakes depending on how hard you are
stopping. The shorter you stop, the more of the vehicle's weight is transferred to the front wheels,
in some cases, causing the rear to lift and the front to dive. These valves are designed to direct
more pressure to the front and less pressure to the rear the harder you stop. This minimizes the
chance of premature lockup at the rear wheels.
• Pressure Differential Valve
This valve is usually mounted just below the master cylinder and is responsible for turning the
brake warning light on when it detects a malfunction. It measures the pressure from the two
sections of the master cylinder and compares them. Since it is mounted ahead of the
proportioning or equalizer valve, the two pressures it detects should be equal. If it detects a
difference, it means that there is probably a brake fluid leak somewhere in the system.
• Combination Valve
The Combination valve is simply a proportioning valve and a pressure differential valve that is
combined into one unit.
Power Brake Booster
The power brake booster is mounted on the firewall directly behind the master cylinder and, along with
the master cylinder, is directly connected with the brake pedal. Its purpose is to amplify the available foot
pressure applied to the brake pedal so that the amount of foot pressure required to stop even the largest
vehicle is minimal. Power for the booster comes from engine vacuum. The automobile engine produces
vacuum as a by-product of normal operation and is freely available for use in powering accessories such
as the power brake operation and is freely available for use in powering accessories such as the power
brake booster. Vacuum enters the booster through a check valve on the booster. The check valve is
connected to the engine with a rubber hose and acts as a one-way valve that allows vacuum to enter the
booster but does not let it escape. The booster is an empty shell that is divided into two chambers by a
rubber diaphragm.
Anti-Lock Brakes (ABS)
The most efficient braking pressure takes place just before each wheel locks up. When you slam on the
brakes in a panic stop and the wheels lock up, causing a screeching sound and leaving strips of rubber
on the pavement, you do not stop the vehicle nearly as short as it is capable of stopping. Also, while the
wheels are locked up, you loose all steering control so that, if you have an opportunity to steer around the
obstacle, you will not be able to do so. Another problem occurs during an extended skid is that you will
burn a patch of rubber off the tire which causes a "flat spot" on the tread that will produce an annoying
thumping sound as you drive.
Anti-lock brake systems solve this lockup problem by rapidly pumping the brakes whenever the system
detects a wheel that is locked up. In most cases, only the wheel that is locked will be pumped, while full
braking pressure stays available to the other wheels. This effect allows you to stop in the shortest
amount of time while maintaining full steering control even if one or more wheels are on ice. The system
uses a computer to monitor the speed of each wheel. When it detects that one or more wheels have
stopped or are turning much slower than the remaining wheels, the computer sends a signal to
momentarily remove and reapply or pulse the pressure to the affected wheels to allow them to continue
turning. This "pumping" of the brakes occurs at ten or more times a second, far faster then a human can
pump the brakes manually. If you step on the brakes hard enough to engage the anti-lock system, you
may feel a strong vibration in the brake pedal. This is a normal condition and indicates that the system is
working, however, it can be disconcerting to some people who don't expect it. If your vehicle has antilock
brakes, read your owner's manual to find out more about it.
Braking systems.PDF (Size: 215.8 KB / Downloads: 120)
The modern automotive brake system has been refined for over 100 years and has become extremely
dependable and efficient.
The typical brake system consists of Disk Brakes in front and either disk or Drum Brakes in the rear
connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder. Other
systems that are connected with the brake system include the parking brake, power brake booster and
the anti-lock system.
When you step on the brake pedal, you are actually pushing against a plunger in the master cylinder
which forces hydraulic oil (brake fluid) through a series of tubes and hoses to the braking unit at each
wheel. Since hydraulic fluid (or any fluid for that matter) cannot be compressed, pushing fluid through a
pipe is just like pushing a steel bar through a pipe. Unlike a steel bar, however, fluid can be directed
through many twists and turns on its way to its destination, arriving with the exact same motion and
pressure that it started with. It is very important that the fluid is pure liquid and that there are no air
bubbles in it. Air can compress, which causes a sponginess to the pedal and severely reduced braking
efficiency. If air is suspected, then the system must be bled to remove the air. There are "bleeder screws"
at each wheel cylinder and caliper for this purpose.
Master Cylinder
The master cylinder is located in the engine compartment on
the firewall, directly in front of the driver's seat. A typical master
cylinder is actually two completely separate master cylinders in
one housing, each handling two wheels. This way if one side
fails, you will still be able to stop the car. The brake warning
light on the dash will light if either side fails, alerting you to the
problem. Master cylinders have become very reliable and rarely
malfunction; however, the most common problem that they
experience is an internal leak.
This will cause the brake pedal to slowly sink to the floor when your foot applies steady pressure. Letting
go of the pedal and immediately stepping on it again brings the pedal back to normal height.
Brake Fluid
Brake fluid is a special oil that has specific properties. It is designed to withstand cold temperatures
without thickening as well as very high temperatures without boiling. (If the brake fluid should boil, it will
cause you to have a spongy pedal and the car will be hard to stop.) Brake fluid must meet standards that
are set by the Department of Transportation(DOT). The current standard is DOT-3 which has a boiling
point of 460º F. But check your owners manual to see what your vehicle manufacturer recommends.
The brake fluid reservoir is on top of the master cylinder. Most cars today have a transparent reservoir so
that you can see the level without opening the cover. The brake fluid level will drop slightly as the brake
pads wear. This is a normal condition and no cause for concern. If the level drops noticeably over a short
period of time or goes down to about two thirds full, have your brakes checked as soon as possible. Keep
the reservoir covered except for the amount of time you need to fill it and never leave a can of brake fluid
uncovered. Brake fluid must maintain a very high boiling point .Exposure to air will cause the fluid to
absorb moisture which will lower that boiling point.
Other Components in the Hydraulic System
• Proportioning valve or Equalizer Valve
These valves are mounted between the master cylinder and the rear wheels. They are designed
to adjust the pressure between the front and rear brakes depending on how hard you are
stopping. The shorter you stop, the more of the vehicle's weight is transferred to the front wheels,
in some cases, causing the rear to lift and the front to dive. These valves are designed to direct
more pressure to the front and less pressure to the rear the harder you stop. This minimizes the
chance of premature lockup at the rear wheels.
• Pressure Differential Valve
This valve is usually mounted just below the master cylinder and is responsible for turning the
brake warning light on when it detects a malfunction. It measures the pressure from the two
sections of the master cylinder and compares them. Since it is mounted ahead of the
proportioning or equalizer valve, the two pressures it detects should be equal. If it detects a
difference, it means that there is probably a brake fluid leak somewhere in the system.
• Combination Valve
The Combination valve is simply a proportioning valve and a pressure differential valve that is
combined into one unit.
Power Brake Booster
The power brake booster is mounted on the firewall directly behind the master cylinder and, along with
the master cylinder, is directly connected with the brake pedal. Its purpose is to amplify the available foot
pressure applied to the brake pedal so that the amount of foot pressure required to stop even the largest
vehicle is minimal. Power for the booster comes from engine vacuum. The automobile engine produces
vacuum as a by-product of normal operation and is freely available for use in powering accessories such
as the power brake operation and is freely available for use in powering accessories such as the power
brake booster. Vacuum enters the booster through a check valve on the booster. The check valve is
connected to the engine with a rubber hose and acts as a one-way valve that allows vacuum to enter the
booster but does not let it escape. The booster is an empty shell that is divided into two chambers by a
rubber diaphragm.
Anti-Lock Brakes (ABS)
The most efficient braking pressure takes place just before each wheel locks up. When you slam on the
brakes in a panic stop and the wheels lock up, causing a screeching sound and leaving strips of rubber
on the pavement, you do not stop the vehicle nearly as short as it is capable of stopping. Also, while the
wheels are locked up, you loose all steering control so that, if you have an opportunity to steer around the
obstacle, you will not be able to do so. Another problem occurs during an extended skid is that you will
burn a patch of rubber off the tire which causes a "flat spot" on the tread that will produce an annoying
thumping sound as you drive.
Anti-lock brake systems solve this lockup problem by rapidly pumping the brakes whenever the system
detects a wheel that is locked up. In most cases, only the wheel that is locked will be pumped, while full
braking pressure stays available to the other wheels. This effect allows you to stop in the shortest
amount of time while maintaining full steering control even if one or more wheels are on ice. The system
uses a computer to monitor the speed of each wheel. When it detects that one or more wheels have
stopped or are turning much slower than the remaining wheels, the computer sends a signal to
momentarily remove and reapply or pulse the pressure to the affected wheels to allow them to continue
turning. This "pumping" of the brakes occurs at ten or more times a second, far faster then a human can
pump the brakes manually. If you step on the brakes hard enough to engage the anti-lock system, you
may feel a strong vibration in the brake pedal. This is a normal condition and indicates that the system is
working, however, it can be disconcerting to some people who don't expect it. If your vehicle has antilock
brakes, read your owner's manual to find out more about it.