2. Objectives
 Discuss application of Pascal’s Law in
brake systems
ď‚— Explain purpose and operation of the
brake system
ď‚— Discuss use of power boosters
2
4. Introduction
 Newton’s Law states that an object in
motion tends to stay in motion
ď‚— Brake systems supply equipment to slow a
vehicle and allow safe operation
ď‚— Brake system operation is based on
hydraulic theory
4
5. Hydraulic Theory and Pascal’s
Law
ď‚— Hydraulic Theory Review
ď‚— Liquids cannot be compressed
ď‚— Force applied at one end of a sealed system
results in equal force at other end
ď‚— Fluid pressure can also control forces at work
5
6. Hydraulic Theory and Pascal’s
Law
 Pascal’s Law
ď‚— Pressure applied to fluid in a sealed system is
transmitted equally in all directions and to all
parts of the system
ď‚— Force (F) = Pressure (P) x Area (A)
ď‚— Formula can also be used to calculate mechanical
advantage
6
8. Brake System Operation
ď‚— Automotive Brake Systems
 Use hydraulic theory to transform driver’s input
(mechanical) to a output force (hydraulic) that
applies the brakes
8
9. Brake System Operation
ď‚— Components of a basic brake system
ď‚— Pedal
ď‚— Linkage
ď‚— Master cylinder
ď‚— Lines and hoses
ď‚— Control valves
ď‚— Disc or drum brakes
9
11. Brake System Operation
ď‚— Pedals and Linkages
ď‚— Mounting for pedal is a shaft from
which the pedal hangs downward
ď‚— Pedal is connected to master cylinder with a
pushrod
ď‚— Pushrod between pedal and booster are
usually adjustable
11
12. Brake System Operation
ď‚— Pedals and Linkages
ď‚— Pushrod between booster and master
cylinder may be adjustable
ď‚— Mounting also holds brake light switch
12
13. Brake System Operation
ď‚— Braking-as brakes are being applied:
ď‚— Driver depresses brake, brake fluid is
pressurized by master cylinder
ď‚— Forces fluid through lines to calipers or
wheel cylinders
ď‚— Fluid pressure is equally transmitted to each
component in brake system
13
14. Brake System Operation
ď‚— Brake Fluids
ď‚— Transforms mechanical input of driver
applying pedal
ď‚— Brake fluids have different classifications and
must be used accordingly
14
15. Brake System Operation
ď‚— Brake Fluids
ď‚— Fluid is hygroscopic (absorbs moisture from
air) and requires periodic service to maintain
boiling point safety
 Follow manufacturer’s recommendations,
usually 3yrs/36k miles
15
17. Brake System Operation
ď‚— Power Boosters and Master Cylinders
ď‚— Master cylinder is transformation point
between mechanical and hydraulic
ď‚— Booster uses engine vacuum or hydraulic
pressure from power-steering to boost
pressure created by applying the brake pedal
ď‚— Combination of master cylinder and booster
creates additional pressure required to stop a
vehicle
17
18. Brake System Apply Components
and Operation
ď‚— Master Cylinders
ď‚— Original systems were single-piston
ď‚— One failure disabled whole system
ď‚— Dual or split brake systems were mandated in
1967 for safety reasons
20
19. Brake System Apply Components
and Operation
ď‚— Master Cylinders
ď‚— Dual or split systems can be front/rear or
diagonally split
ď‚— Dual systems can have a failure in one circuit
and still operate
ď‚— At reduced effectiveness
21
20. Control Valves, Lines and Hoses,
and Warning Lights
ď‚— Metering Valves
ď‚— Vehicles with front discs and rear drums
ď‚— Must have metering valves for brake stability
ď‚— Controls application to manage braking
ď‚— Ensures rear brakes apply before front
23
21. Control Valves, Lines and Hoses, and
Warning Lights
ď‚— Proportioning Valves
ď‚— Necessary to apply leading brakes more than
trailing brakes
ď‚— Control pressure to prevent rear-wheel
lockup during hard braking
ď‚— Combination valves combine proportioning
valves and metering valves
24
22. Control Valves, Lines and Hoses, and
Warning Lights
ď‚— Load-Sensing Proportioning Valves
ď‚— Help prevent rear-brake lockup on trucks by
monitoring vehicle load
ď‚— One type monitors height between frame and
rear axle
25
23. Control Valves, Lines and Hoses, and
Warning Lights
ď‚— Load-Sensing Proportioning Valves
ď‚— Another type is part of combination valve and
“senses” as rear of truck rises on hard braking
26
25. Control Valves, Lines and Hoses, and
Warning Lights
ď‚— Lines and Hoses
ď‚— Brake lines are made of steel with flared
fittings at each end
28
26. Control Valves, Lines and Hoses, and
Warning Lights
ď‚— Lines and Hoses
ď‚— Flexible hoses connect from fixed location to
caliper or wheel cylinder to allow for
suspension movement
ď‚— Two types of brake-line fittings
ď‚— Double flare and ISO
29
27. Control Valves, Lines and Hoses, and
Warning Lights
ď‚— Warning Lights
ď‚— Red Brake Warning Light
ď‚— Attached to any of the three following
switches or sensors:
ď‚— Parking brake
ď‚— Brake fluid level sensor
ď‚— Diagonal split system warning light
31