1porter and chester institute. 2 brake hydraulic systems

1

PORTERPORTERANDAND

CHESTERCHESTERINSTITUTEINSTITUTE

2

Brake HydraulicSystems

Brake HydraulicSystems

3Function of the Hydraulic SystemFunction of the Hydraulic System

• The primary purpose of an hydraulic system is to transfer force from the brake pedal to the brake shoes and pads.

• A hydraulic system can also be used to multiply force – in the same manner as a lever multiplies force.

• The primary purpose of an hydraulic system is to transfer force from the brake pedal to the brake shoes and pads.

• A hydraulic system can also be used to multiply force – in the same manner as a lever multiplies force.

4Advantage of using hydraulicsAdvantage of using hydraulics

• Can transfer force over long distances• Can be easily routed around obstacles• Can transfer force to components that move

with the suspension• Never needs adjustment

• Can transfer force over long distances• Can be easily routed around obstacles• Can transfer force to components that move

with the suspension• Never needs adjustment

5

Most liquids are non-compressible.

When pressure is applied to a liquid in and enclosed

system, that pressure is distributed equally and in all

directions throughout the fluid

Pascal’s Law

6Pressure = Force ÷ AreaPressure = Force ÷ Area

• The amount of pressure is determined by the force applied to the piston, divided by the area of the piston

• The amount of pressure is determined by the force applied to the piston, divided by the area of the piston

100 LBS

Piston Area = 1 Square Inch

100 ÷ 1 = 100 LBS Per Square Inch

7Distribution of Pressure Distribution of Pressure

30 PSI30 PSI

30 PSI

30 PSI

30 PSI

1 SquareInch

30 Pounds

Pressure is distributed equally and in all directions.

8Cylinder Bore and StrokeCylinder Bore and Stroke

• The size of the piston is generally expressed as its ‘bore’ diameter.

• The distance that the piston moves is called the ‘stroke’.

• The size of the piston is generally expressed as its ‘bore’ diameter.

• The distance that the piston moves is called the ‘stroke’.

9

The relationship between area and pressureThe relationship between area and pressure

• A smaller piston will generate more pressure• A smaller piston will generate more pressure

100 LBS

1/2 Square Inch

100 ÷ .5 = 200 LBS Per Square Inch

10

The relationship between area and pressureThe relationship between area and pressure

• A larger piston will generate less pressure• A larger piston will generate less pressure

100 LBS

2 Square Inches 100 ÷ 2 = 50 LBS Per Square Inch

11

Using hydraulic pressure to transmit forceUsing hydraulic pressure to transmit force

Master Cylinder Slave Cylinder

Hydraulic Line

12

If Bores of Master and Slave Cylinders are the sameIf Bores of Master and Slave Cylinders are the same

• If the bore of the master cylinder is the same as the bore of the slave cylinder then the amount of force generated at the slave is the same as the force applied to the master cylinder.

• The stroke of the slave cylinder will be the same as the same as the stroke of the master cylinder.

• If the bore of the master cylinder is the same as the bore of the slave cylinder then the amount of force generated at the slave is the same as the force applied to the master cylinder.

• The stroke of the slave cylinder will be the same as the same as the stroke of the master cylinder.

13

Master and Slave with Same Size BoresMaster and Slave with Same Size Bores

100 Pounds

1 in

ch

1 in

ch


Hydraulic Line

100 Pounds

14

Hydraulic AdvantageHydraulic Advantage

• If the master cylinder is smaller than the slave cylinder there will be a multiplication of force

• There will be more force output at the slave than input at the master

• The stroke that the master cylinder piston moves through will be longer

• The ratio of the area of the slave cylinder bore ÷ the area of the master cylinder bore determines the hydraulic advantage

• If the master cylinder is smaller than the slave cylinder there will be a multiplication of force

• There will be more force output at the slave than input at the master

• The stroke that the master cylinder piston moves through will be longer

• The ratio of the area of the slave cylinder bore ÷ the area of the master cylinder bore determines the hydraulic advantage

15

If Master and Slave have Different Bore DiametersIf Master and Slave have Different Bore Diameters


100 Pounds

400 Pounds

1 in

ch

¼

inch

Bore = 1 Sq. In. Bore = 4 Sq. In.

16Using Hydraulic Pressure to Transmit Force

Using Hydraulic Pressure to Transmit Force• A hydraulic master and slave

cylinder can transfer force over long distances without loss of power.

• It can also transmit force through sharp angles and around obstacles easily

• It can easily connect components that are vibrating or rocking - as in a clutch linkage.

• A hydraulic master and slave cylinder can transfer force over long distances without loss of power.


• It can easily connect components that are vibrating or rocking - as in a clutch linkage.

Flexible rubberhose

17

Transferring force over a distanceTransferring force over a distance



• It can easily connect components that are moving slightly as in a clutch linkage or suspension system.



• It can easily connect components that are moving slightly as in a clutch linkage or suspension system.

18

Force Multiplication Using LeverageForce Multiplication Using Leverage

A mechanical advantage of 4 to 1 is the result of the ratio of the length between the brake pedal and pivot point divided by the distance from the pivot point to

the clevis pin

8”

2”

50 Pounds at the brake

pedal

200 Pounds at the

master cylinder piston

1 square inch cylinder

bore

200 PSI200 PSI

Clevis Pin

Pivot Pin

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Force Multiplication Using Hydraulic AdvantageForce Multiplication Using Hydraulic Advantage

The amount of pressure at the brakes is equal to the size of the cylinder bores multiplied by the pressure

200 PSI200 PSI

Caliper bore = 4 square

Inch

Pivot Pin

Wheel cylinder

bore = 1.5 square Inch

800 lbs.800 lbs.

300 lbs.

300 lbs.

300 lbs.

300 lbs.

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Brake FluidBrake Fluid

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Properties of Brake FluidProperties of Brake Fluid

1) Non-Compressible2) Very low freezing point3) Very high boiling point4) Non-Corrosive5) Compatible with rubber used in

brake system6) Good lubricant7) Hygroscopic [absorbs water]8) Compatibility with other brands and

types of brake fluid

1) Non-Compressible2) Very low freezing point3) Very high boiling point4) Non-Corrosive5) Compatible with rubber used in

brake system6) Good lubricant7) Hygroscopic [absorbs water]8) Compatibility with other brands and

types of brake fluid

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DOT Sets StandardsDOT Sets Standards

• The US Department of Transportation [DOT] sets specifications and standards for brake fluid

• The SAE [Society of Automotive Engineers] also sets standards

• The US Department of Transportation [DOT] sets specifications and standards for brake fluid

• The SAE [Society of Automotive Engineers] also sets standards

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DOT designation is based on boiling temperature DOT designation is based on boiling temperature

• DOT 3 – Most Common Type in use today• DOT 4 – Higher Boiling Point than DOT 3

– Often required by European car manufacturers

• DOT 5 – Highest Boiling Point Available– Used for racing and super high performance

vehicles

• DOT 3 – Most Common Type in use today• DOT 4 – Higher Boiling Point than DOT 3

– Often required by European car manufacturers

• DOT 5 – Highest Boiling Point Available– Used for racing and super high performance

vehicles

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DOT Fluid Boiling PointDOT Fluid Boiling Point

Wet Boiling Point

284

311

356

Dry Boiling Point

401

446

500

DOT 3

DOT 4

DOT 5

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Why is Boiling Point Important?Why is Boiling Point Important?

• When DOT 3 fluid becomes fully saturated with moisture its boiling point drops 1170 F

• When brake fluid boils it forms gas bubbles• The gas bubbles are compressible – just like

air• If the brake fluid is allowed to boil the pedal

will go to the floor and the vehicle will not slow or stop!

• When DOT 3 fluid becomes fully saturated with moisture its boiling point drops 1170 F

• When brake fluid boils it forms gas bubbles• The gas bubbles are compressible – just like

air• If the brake fluid is allowed to boil the pedal

will go to the floor and the vehicle will not slow or stop!

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Why Does Brake Fluid Get Saturated With MoistureWhy Does Brake Fluid Get Saturated With Moisture

• The flexible rubber hoses that connect the master cylinder to the calipers and drums allow a small amount of moisture into the system through Osmosis

• Whenever the fluid filler cap is removed for service the fluid is exposed to the moisture in the air

• The flexible rubber hoses that connect the master cylinder to the calipers and drums allow a small amount of moisture into the system through Osmosis

• Whenever the fluid filler cap is removed for service the fluid is exposed to the moisture in the air

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POLY-GLYCOL BASED FLUIDPOLY-GLYCOL BASED FLUID

• Made of Glycol-Ether compounds• Made from vegetable oil not from

petroleum• Very hygroscopic – absorbs moisture• Is used for both DOT 3 and DOT 4 fluids• Additives are used in both DOT 3 and

DOT 4 fluid to neutralize water held in suspension

• Will dissolve or discolor the paint on most cars!

• Made of Glycol-Ether compounds• Made from vegetable oil not from

petroleum• Very hygroscopic – absorbs moisture• Is used for both DOT 3 and DOT 4 fluids• Additives are used in both DOT 3 and

DOT 4 fluid to neutralize water held in suspension

• Will dissolve or discolor the paint on most cars!

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LMA TYPE BRAKE FLUIDLMA TYPE BRAKE FLUID

• ‘LOW MOISTURE ACTIVITY’• Recommended by many European car

manufactures• Additives in fluid help prevent deterioration

of rubber seals in hydraulic system made from natural rubber compounds

• Manufactured by Castrol as a DOT 4 type fluid

• ‘LOW MOISTURE ACTIVITY’• Recommended by many European car

manufactures• Additives in fluid help prevent deterioration

of rubber seals in hydraulic system made from natural rubber compounds

• Manufactured by Castrol as a DOT 4 type fluid

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SILICON BASED FLUIDSILICON BASED FLUID

• Very high boiling point • Marketed in the 1980’s as a DOT 5 fluid• Not hygroscopic – does not mix with water

at all• Tends to aerate when cycled rapidly

– This property makes silicone based fluid unacceptable for modern cars with ABS brake systems!

• Has no harmful effect on painted surfaces

• Very high boiling point • Marketed in the 1980’s as a DOT 5 fluid• Not hygroscopic – does not mix with water

at all• Tends to aerate when cycled rapidly

– This property makes silicone based fluid unacceptable for modern cars with ABS brake systems!

• Has no harmful effect on painted surfaces

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DOT 5.1 FluidDOT 5.1 Fluid

• Recently brake fluid manufactures have been able to formulate a poly-glycol based fluid that meets the requirements for DOT 5 fluids.

• Since DOT 5 has been associated with silicone based fluid this non silicone fluid is referred to as DOT 5.1

• Recently brake fluid manufactures have been able to formulate a poly-glycol based fluid that meets the requirements for DOT 5 fluids.

• Since DOT 5 has been associated with silicone based fluid this non silicone fluid is referred to as DOT 5.1

31

What Type of Fluid Should Be UsedWhat Type of Fluid Should Be Used

• Most modern cars have the fluid type printed on the master cylinder filler cap

• Most modern cars have the fluid type printed on the master cylinder filler cap

32

Handling Brake FluidHandling Brake Fluid

• Brake fluid must always be kept in a sealed container

• If the cap is left off a container of brake fluid for 24 hours or more it should be discarded

• Never use an open container of fluid that you don’t recognize or remember where it came from

• Brake fluid must always be kept in a sealed container

• If the cap is left off a container of brake fluid for 24 hours or more it should be discarded

• Never use an open container of fluid that you don’t recognize or remember where it came from

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• Brake fluid is clear or slightly amber in color – just like many other fluids – just because its in a container that says its brake fluid doesn’t necessarily mean it actually is brake fluid or is not contaminated with other fluids

• The risk of injury to people and property is too great to justify saving a few cents

• Brake fluid is clear or slightly amber in color – just like many other fluids – just because its in a container that says its brake fluid doesn’t necessarily mean it actually is brake fluid or is not contaminated with other fluids

• The risk of injury to people and property is too great to justify saving a few cents

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• All new containers of brake fluid have a seal under the cap that must be broken before use

• If the seal is broken and you are not sure how old the fluid is – discard it !

• Never transfer new brake fluid into another container

• All new containers of brake fluid have a seal under the cap that must be broken before use

• If the seal is broken and you are not sure how old the fluid is – discard it !

• Never transfer new brake fluid into another container

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• Do not allow brake fluid to come into contact with the painted surfaces of the car body

• If you accidentally get brake fluid on the paint work of a car – rinse it off with a garden hose – do not wipe it off with a rag

• Do not allow brake fluid to come into contact with the painted surfaces of the car body

• If you accidentally get brake fluid on the paint work of a car – rinse it off with a garden hose – do not wipe it off with a rag

©2005 PORTER AND CHESTER INSTITUTE / CONNECTICUT SCHOOL OF ELECTRONICS

36


• Brake fluid should be changed every 2 years or 30 k miles

• Brake fluid turns grey and then black as the rubber components of the brake system deteriorate

• If you get brake fluid on you skin rinse it off immediately

• If you get brake fluid in you eyes – thoroughly rinse your eyes with clean water – see a physician immediately!

• Brake fluid should be changed every 2 years or 30 k miles

• Brake fluid turns grey and then black as the rubber components of the brake system deteriorate

• If you get brake fluid on you skin rinse it off immediately

• If you get brake fluid in you eyes – thoroughly rinse your eyes with clean water – see a physician immediately!

37

Petroleum Based Fluids & BrakesPetroleum Based Fluids & Brakes

• If a petroleum based fluid; motor oil, transmission fluid, power steering fluid – is accidentally introduced into the brake hydraulic system the rubber components will be destroyed.

• All of the brake hydraulic components must be replaced – the steel lines can be flushed out with alcohol

• If a petroleum based fluid; motor oil, transmission fluid, power steering fluid – is accidentally introduced into the brake hydraulic system the rubber components will be destroyed.

• All of the brake hydraulic components must be replaced – the steel lines can be flushed out with alcohol

38

Petroleum Based Fluids & BrakesPetroleum Based Fluids & Brakes• A sure sign of fluid contamination is

distortion of the rubber seal on the master cylinder filler cap

• If this seal appears to be melted, stretched, swollen or otherwise distorted the vehicle is unsafe to drive

• A complete overhaul of the brake hydraulic system will be required

• A sure sign of fluid contamination is distortion of the rubber seal on the master cylinder filler cap

• If this seal appears to be melted, stretched, swollen or otherwise distorted the vehicle is unsafe to drive

• A complete overhaul of the brake hydraulic system will be required

39

Master CylindersMaster

Cylinders

40

Single Piston Master CylinderSingle Piston Master Cylinder

• Used prior to 1968• Used prior to 1968

Single Spool Type Piston

High Pressure Lip Seal

Low Pressure Lip Seal

FluidReservoir

Vent Port Replenishing Port

41

Single Piston Master CylinderSingle Piston Master Cylinder

• When Brake Pedal is Depressed

• When Brake Pedal is Depressed

Piston is Moved Forward

by Brake Pedal

Lip Seal Closes Vent Port

Pressure Rises in Chamber

Pressurized Brake Fluid is Sent to Wheel

Cylinders

42

Master Cylinder OperationMaster Cylinder Operation

• When the lip seal passes over the vent port pressure builds up in the chamber

• When the lip seal passes over the vent port pressure builds up in the chamber

43

Pumping the Brake PedalPumping the Brake Pedal

• When the brake pedal is cycle rapidly fluid can be drawn into the working chamber through holes drilled in the piston land and around the lip seal

• When the brake pedal is cycle rapidly fluid can be drawn into the working chamber through holes drilled in the piston land and around the lip seal

44

Single Piston Hydraulic SystemSingle Piston Hydraulic System

• One piston / cylinder provides all the fluid pressure for all 4 brakes

• One piston / cylinder provides all the fluid pressure for all 4 brakes

45Single Piston Hydraulic SystemSingle Piston Hydraulic System

• When the brake pedal is depressed fluid is distributed evenly to all 4 wheel cylinders

• When the brake pedal is depressed fluid is distributed evenly to all 4 wheel cylinders

46

Brake Failure in a Single Piston SystemBrake Failure in a Single Piston System

• If any component in this system fails the

entire brake system is inoperative

• If any component in this system fails the

entire brake system is inoperative

47

Dual Piston Master CylinderDual Piston Master Cylinder

• All Modern Cars and Trucks built after 1968 use a Dual Circuit Master Cylinder

• All Modern Cars and Trucks built after 1968 use a Dual Circuit Master Cylinder

48

Master Cylinder ComponentsMaster Cylinder Components

Cylinder Body

Reservoir

Primary Piston

Secondary Piston

Return Springs

49Dual Hydraulic CircuitsDual Hydraulic Circuits

• Having two separate hydraulic circuits insures that we will have at least

two working brakes in the event of a failure



50

Dual Hydraulic CircuitsDual Hydraulic Circuits





51

Dual Hydraulic CircuitsDual Hydraulic Circuits

• If one of the rear wheel cylinders has a leak

there will still be adequate hydraulic

pressure to stop the car with the front brakes

• If one of the rear wheel cylinders has a leak

there will still be adequate hydraulic

pressure to stop the car with the front brakes

52

Master Cylinder OperationMaster Cylinder Operation

• In normal braking pressure developed in the primary chamber is applied to the secondary piston

• The pressure on the rear of the secondary piston is transferred into the secondary chamber

• In normal braking pressure developed in the primary chamber is applied to the secondary piston

• The pressure on the rear of the secondary piston is transferred into the secondary chamber

Primary Chamber

Secondary Chamber

53Primary Circuit FailurePrimary Circuit Failure

• If the primary circuit fails [leaks] the primary piston will until forward it makes contact with the secondary piston

• If the primary circuit fails [leaks] the primary piston will until forward it makes contact with the secondary piston

Extension on the primary

piston makes contact with secondary

piston

54Secondary Circuit FailureSecondary Circuit Failure

• If the secondary circuit fails the secondary piston will bottom out in the cylinder bore

• The primary piston will still be able to develop pressure

• If the secondary circuit fails the secondary piston will bottom out in the cylinder bore

• The primary piston will still be able to develop pressure

55

Vent PortsVent Ports• Vent Ports

{Compensating Ports} allow fluid to flow into the chamber when the brake pedal is not depressed

• Vent Ports {Compensating Ports} allow fluid to flow into the chamber when the brake pedal is not depressed

• Fluid returns to the reservoir through the vent port when the brakes are released

56

Replenishing PortsReplenishing Ports

• The replenishing port allows fluid from the reservoir to fill the low pressure chamber behind the front piston land

• The replenishing port is always open to the reservoir

• The replenishing port allows fluid from the reservoir to fill the low pressure chamber behind the front piston land

• The replenishing port is always open to the reservoir

57

Quick Take Up Type Master CylinderQuick Take Up Type Master Cylinder

• Provides better fuel economy by reducing brake drag

• Provides better fuel economy by reducing brake drag

58

Quick Take Up Type Master CylinderQuick Take Up Type Master Cylinder

• Introduced in 1980 on GM X-body• Adopted by many manufactures since• Used to reduce rolling drag caused by

contact between pad and rotor• Special design caliper pulls brake pad

slightly away from rotor when brakes are not applied

• Additional fluid volume is needed to compensate for the fluid that is displaced by pad pull back

• Introduced in 1980 on GM X-body• Adopted by many manufactures since• Used to reduce rolling drag caused by

contact between pad and rotor• Special design caliper pulls brake pad

slightly away from rotor when brakes are not applied

• Additional fluid volume is needed to compensate for the fluid that is displaced by pad pull back

59

Step Bore DesignStep Bore Design

Small forward bore for high pressure in normal braking

Larger rear bore – for additional fluid displacement of quick take up

calipers

602 Stage Operation2 Stage Operation

• Initial ‘take up’ stage• Extra volume of rear section of cylinder is

pushed over and around lip seals and enters both operating chambers

• ‘Take up volume’ pushes pads out into contact with rotor

• Until pads come into contact with rotor pressure in system is very low

• Initial ‘take up’ stage• Extra volume of rear section of cylinder is

pushed over and around lip seals and enters both operating chambers

• ‘Take up volume’ pushes pads out into contact with rotor

• Until pads come into contact with rotor pressure in system is very low

61

Take-Up StageTake-Up Stage

When the brakes are initially applied the extra volume of fluid in the rear chamber passes around the lip seals of the primary piston and into the primary chamber

62Pressure StagePressure Stage

• Once pads contact rotor pressure rapidly builds up

• Fluid pressure in large rear section of master cylinder is allowed to vent back to reservoir through ‘quick take up valve

• Once pads contact rotor pressure rapidly builds up

• Fluid pressure in large rear section of master cylinder is allowed to vent back to reservoir through ‘quick take up valve

63Take-Up StageTake-Up Stage

When the pads come into contact with the rotors pressure builds up

The quick take up valve opens to allow fluid in the rear chamber to vent to the reservoir

Quick Take-up

Valve opens

64

Brake CircuitsBrake

Circuits

65

Weight Applied to TiresWeight Applied to Tires

• The brake force needed to bring the vehicle to a stop is proportional to the weight applied to each set of wheels [axle]

• The brake force needed to bring the vehicle to a stop is proportional to the weight applied to each set of wheels [axle]

2250 lbs. 1250 lbs.

66

How Weight Effects Brake PerformanceHow Weight Effects Brake Performance

• The more weight that is applied to a wheel - the harder the brake must work to slow that wheel

• Nearly all vehicles have the engine and transmission located over the front axle

• In general the brakes at the front axle must work harder than those at the rear because they carry more of the vehicle weight

• The more weight that is applied to a wheel - the harder the brake must work to slow that wheel

• Nearly all vehicles have the engine and transmission located over the front axle

• In general the brakes at the front axle must work harder than those at the rear because they carry more of the vehicle weight

67

Weight Transfer During BrakingWeight Transfer During Braking

• All vehicles experience a weight transfer toward the front of a vehicle as the vehicle is brought to a stop

• All vehicles experience a weight transfer toward the front of a vehicle as the vehicle is brought to a stop

Increased weight on

front wheels

Decreased weight on

rear wheels

Weight

68

Weight TransferWeight Transfer

• Weight transfer during deceleration puts an additional load on the front brakes.

• The inertia of the vehicle during braking transfers force from the rear to the front effectively decreasing the weight on the rear wheels and increasing the weight applied to the front wheels

• Weight transfer during deceleration puts an additional load on the front brakes.

• The inertia of the vehicle during braking transfers force from the rear to the front effectively decreasing the weight on the rear wheels and increasing the weight applied to the front wheels

69

Front Brake BiasFront Brake Bias

• Because of the extra weight the front wheels carry and the weight transfer to the front during braking the front brakes do more of the braking than the rear

• For this reason the front brakes must be larger and more effective than the rear brakes

• Trucks that haul heavy loads are the only type of vehicle that require rear brakes that are equal to or more effective than the front brakes

• Because of the extra weight the front wheels carry and the weight transfer to the front during braking the front brakes do more of the braking than the rear

• For this reason the front brakes must be larger and more effective than the rear brakes

• Trucks that haul heavy loads are the only type of vehicle that require rear brakes that are equal to or more effective than the front brakes

70

Brake BiasBrake Bias

• Brake Bias is the term given to the relative percentage of braking work done by the front and rear brakes of a vehicle in a forward stop.

• Brake bias is expressed in percentage on the front and rear axle [ 50/50, 60/40 etc.]

• Brake Bias is the term given to the relative percentage of braking work done by the front and rear brakes of a vehicle in a forward stop.

• Brake bias is expressed in percentage on the front and rear axle [ 50/50, 60/40 etc.]

71

Typical Brake Bias PercentagesTypical Brake Bias Percentages

RWD 50/50RWD 50/50

FWD 70/30

Truck – varies with load

72

50 / 50 Brake Bias on RWD50 / 50 Brake Bias on RWD

• Rear wheel drive vehicles have a brake bias the ranges from 50/50 to 60/40

• Rear wheel drive vehicles have a brake bias the ranges from 50/50 to 60/40

50 of braking done by front

brakes

50 of braking done by rear

brakes

73

Brake Bias for Front DriveBrake Bias for Front Drive

• Front wheel drive cars have a front rear brake bias of 70/30 and higher

• Front wheel drive cars have a front rear brake bias of 70/30 and higher

70% of Brake Effort done by the Front

Brakes

30% of Brake Effort done by the Rear

Brakes

74

Hydraulic CircuitsHydraulic Circuits

• Because there is fundamental differences in the requirements for a rear drive brake system and a front drive brake system, two different types of hydraulic system are needed

– Rear drive vehicles use a front / rear split hydraulic system

– Front drive vehicles use a dual diagonal hydraulic system

• In addition to the type of hydraulic circuit used in front drive and rear drive vehicles there are difference in the types of hydraulic control valves as well

• Because there is fundamental differences in the requirements for a rear drive brake system and a front drive brake system, two different types of hydraulic system are needed

– Rear drive vehicles use a front / rear split hydraulic system

– Front drive vehicles use a dual diagonal hydraulic system

• In addition to the type of hydraulic circuit used in front drive and rear drive vehicles there are difference in the types of hydraulic control valves as well

75

Front /Rear Split Hydraulic CircuitFront /Rear Split Hydraulic Circuit

• Used on nearly all Rear Drive cars and

light trucks

• Used on nearly all Rear Drive cars and

light trucks

76

Front / Rear Split Dual CircuitFront / Rear Split Dual Circuit

• One chamber of the master cylinder feeds both front brake cylinders – the other chamber feeds the rear cylinders

• As the brake bias is nearly 50/50 if one circuit fails due to a leak the other circuit can provide nearly 50% of the normal braking effort

• This will allow the vehicle to stop within a reasonable distance [although not as quickly as with a fully functioning braking system]

• One chamber of the master cylinder feeds both front brake cylinders – the other chamber feeds the rear cylinders

• As the brake bias is nearly 50/50 if one circuit fails due to a leak the other circuit can provide nearly 50% of the normal braking effort

• This will allow the vehicle to stop within a reasonable distance [although not as quickly as with a fully functioning braking system]

77

Front / Rear Split Dual CircuitFront / Rear Split Dual Circuit

• Since the disc brakes require a greater volume of fluid the fluid reservoirs will have different volumes – the large reservoir will be for the front brakes the smaller one for the rear

• Since the disc brakes require a greater volume of fluid the fluid reservoirs will have different volumes – the large reservoir will be for the front brakes the smaller one for the rear

• On a disc / drum system one chamber of the master cylinder will feed only the disc brakes

Disc BrakesDrum

Brakes

78

Why a Front/Rear Split Wont work on FWDWhy a Front/Rear Split Wont work on FWD

• If a front / rear split were used on a FWD vehicle; then if a failure occurs in the front hydraulic circuit, the rear circuit could provide only 30% of the braking effort needed to slow the vehicle

• Since there is so little weight carried by the rear wheels increasing the rear braking efficiency would cause the rear wheels to lock up – thus promoting a skid

• If a front / rear split were used on a FWD vehicle; then if a failure occurs in the front hydraulic circuit, the rear circuit could provide only 30% of the braking effort needed to slow the vehicle

• Since there is so little weight carried by the rear wheels increasing the rear braking efficiency would cause the rear wheels to lock up – thus promoting a skid

79Why a Left / Right Split Wont WorkWhy a Left / Right Split Wont Work

• If the brake system is split left / right then in the event of a failure only the brakes on one side of the vehicle would work

• In a panic stop the vehicle would swerve left into oncoming traffic or right into the gutter

• If the brake system is split left / right then in the event of a failure only the brakes on one side of the vehicle would work

• In a panic stop the vehicle would swerve left into oncoming traffic or right into the gutter

80

Dual Diagonal Brake CircuitDual Diagonal Brake Circuit

• Used on all FWD vehicles

• Used on all FWD vehicles

81


• The solution for front drive brake hydraulic circuit was to split the system on a diagonal – Connecting one chamber of the master cylinder

to the left front and right rear brakes– The other chamber is connected to the right

front and left rear

• The solution for front drive brake hydraulic circuit was to split the system on a diagonal – Connecting one chamber of the master cylinder

to the left front and right rear brakes– The other chamber is connected to the right

front and left rear

82


• In the event that any one hydraulic component fails there will be one front and one rear brakes still working

• The two working brakes will be on opposite sides of the car [Left to Right] so there will be no pull if one circuit fails

• In the event that any one hydraulic component fails there will be one front and one rear brakes still working

• The two working brakes will be on opposite sides of the car [Left to Right] so there will be no pull if one circuit fails

©2005 Porter and Chester Institute / Connecticut School of Electronics

83

Trucks and SUVsTrucks and SUVs

• Trucks and SUVs have a significant portion of their weight located over the rear axle and will normally use front / rear split brake systems

• Light unit body SUVs based on FWD drivelines [Subaru, Honda CRV etc.] use dual diagonal brake systems as they have a high forward brake bias

• Trucks and SUVs have a significant portion of their weight located over the rear axle and will normally use front / rear split brake systems

• Light unit body SUVs based on FWD drivelines [Subaru, Honda CRV etc.] use dual diagonal brake systems as they have a high forward brake bias

84

PORTERPORTERANDAND

CHESTERCHESTERINSTITUTEINSTITUTE

1porter and chester institute. 2 brake hydraulic systems

Documents

master cylinder piston

force area

hydraulic pressure

force output

multiplication of force

square inch slide

pounds slide

adjustment slide