Quick notes on braking systems

1. Geometrical and Mechanical Engineering
Drawing- CAPE Unit II
Brakes
A brake is a mechanical device which inhibits motion, slowing or stopping a moving object or
preventing its motion. A vehicle brake is a brake used to slow down a vehicle by converting
its kinetic energy into heat. The basic hydraulic system, most commonly used, usually has six
main stages: the brake pedal, the brake boost (vacuum servo), the master cylinder, the
apportioning valves, and finally the road wheel brakes themselves.
Brakes convert motion to heat, and if the brakes get too hot, they become less effective, a
phenomenon known as brake fade.
Drum Brake
A drum brake is a brake that uses friction caused by a set of shoes or pads that press against a
rotating drum-shaped part called a brake drum. These do not apply brakes immediately, are
complex and must be large to cope with the load. As the brake linings wear, the shoes must
travel a greater distance to reach the drum. When the distance reaches a certain point, a self-
adjusting mechanism automatically reacts by adjusting the rest position of the shoes so that
they are closer to the drum. Here, the adjusting lever rocks enough to advance the adjuster
gear by one tooth. The adjuster has threads on it, like a bolt, so that it unscrews a little bit when
it turns, lengthening to fill in the gap
Parts of the Drum Brake
Backing Plate: The backing plate provides a base for the other components. It attaches to the
axle sleeve and provides a non-rotating rigid mounting surface for the wheel cylinder, brake
shoes, and assorted hardware. Strong and wear resistant.
Brake Drum: made of a special type of cast iron that is heat-conductive and wear-resistant,
rotates with the wheel and axle. When brakes are applies, the lining pushes radially against the
inner surface of the drum causing friction to slow or stop rotation of the wheel and axle. Heat
generated
Wheel cylinder: One wheel cylinder operates the brake on each wheel. Two pistons operate
the shoes, one at each end of the wheel cylinder. Hydraulic pressure from the master cylinder
acts on the piston cup, pushing the pistons toward the shoes, forcing them against the drum.
When brakes are released, brake shoe springs restore the shoes to their original (disengaged)
position.

2. Brake shoe: the part of a braking system which carries the brake lining in the drum brakes used
on automobiles, or the brake block in train brakes and bicycle brakes. Brake shoes take longer
to dissipate heat than disc brakes but are more effective at setting parking brakes.
Single Shoe System (SLS)
The leading shoe is "dragged" into the friction surface of the drum and thus achieving greater
braking force. The other shoe is "trailing", moving against the direction of rotation, is thrown
away from the friction surface of the drum and is far less effective. It is equally effective
whether the vehicle is travelling forwards or in reverse where the leading and trailing brake
shoes’ roles are switched.
Dual ShoeSystem(2LS)
The twin-leading-shoe brake (2LS) is a type of drum brake that has two leading shoes, rather
than the single leading shoe and a single trailing shoe of a single-leading shoe (SLS) drum brake.
A leading shoe has a self-servo effect, so an advantage of a 2LS is that it provides the maximum
retardation in its intended direction of travel, i.e. forwards. 2LS brakes are fitted on the front
axle of automobiles, or the front wheel of a motorcycle. A 2LS brake is more powerful than
an SLS design since both shoes apply full braking force. In reverse, BOTH shoes become trailing
and are virtually useless since the drum rotation tries to throw it off the drum. Hence why the
rear wheels of the vehicle usually has the SLS system.
Disc Brake
A disc brake is a wheel brake that slows rotation of the wheel by the friction caused by
pushing brake pads against a brake disc with a set of callipers. The brake disc or rotor in is
usually made of cast iron or ceramic/matrix or carbon composites which is connected to the
wheel and/or the axle. To stop the wheel, friction material in the form of brake pads, mounted

3. on a device called a brake calliper, is forced mechanically, hydraulically, pneumatically, or
electromagnetically against both sides of the disc. Friction causes the disc and attached wheel
to slow or stop.
Parts of the Disc Brake
Brake Pad: steel backing plates with friction material bound to the surface that faces the disk
brake rotor. Better stopping power than drum brakes and more resistant to brake fade.
However, no self-servo effect. Made of asbestos or some other composite or ceramic.
Brake Calliper: Callipers are of two types, floating or fixed. A fixed calliper does not move
relative to the disc and is thus less tolerant of disc imperfections. It uses one or more single or
pairs of opposing pistons to clamp from each side of the disc, and is more complex and
expensive than a floating calliper.
A floating calliper (also called a "sliding calliper") moves with respect to the disc, along a line
parallel to the axis of rotation of the disc; a piston on one side of the disc pushes the inner
brake pad until it makes contact with the braking surface, then pulls the calliper body with the
outer brake pad so pressure is applied to both sides of the disc.
Brake Piston: The most common calliper design uses a single hydraulically actuated piston
within a cylinder, although high performance brakes use as many as twelve. Modern cars use
different hydraulic circuits to actuate the brakes on each set of wheels as a safety measure. The
hydraulic design also helps multiply braking force. The number of pistons in a calliper is often
referred to as the number of 'pots', so if a vehicle has 'six pot' callipers it means that each
calliper houses six pistons.
Brake Bleeding: procedure performed on hydraulic brake systems whereby the brake lines (the
pipes and hoses containing the brake fluid) are purged of any air bubbles.

4. Brake Fluid
Brake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch applications
in automobiles, motorcycles, light trucks, and some bicycles. It is used to transfer force into
pressure, and to amplify braking force. It works because liquids are not
appreciably compressible.
Most brake fluids used today are glycol-ether based, but mineral oil and silicone based fluids
are also available.
Boiling point: boiling point of brake fluid must be very high to ensure liquid does not vaporize
since gas is relatively very compressible to liquid, wet boiling point describes when the brake
fluid has absorbed a certain percentage of moisture and dry in its pure state
Viscosity: For reliable, consistent brake systemoperation, brake fluid must maintain a constant
viscosity under a wide range of temperatures, including extreme cold.
Corrosion: Brake fluids must not corrode the metals used inside components such as callipers’,
wheel cylinders, master cylinders and ABS control valves. They must also protect against
corrosion as moisture enters the system. Additives (corrosion inhibitors) are added to the base
fluid to accomplish this.
Compressibility: Brake fluids must maintain a low level of compressibility that remains low,
even with varying temperatures to accommodate different environmental conditions. This is
important to insure consistent brake pedal feel. As compressibility increases a greater amount
of brake pedal stroke is necessary for the same amount of brake calliper piston stroke.
Parking Brakes
This uses only cables and levers and bypasses the hydraulic system as a fail-safe measure. The brake
cable passes through and intermediate lever, increasing force and then passes through a U-shaped
equalizer which splits the force in two and sends it evenly through cables connected through the rear
wheels. In drum brakes, the cable runs straight to the brake shoe. In rear disc brakes, a calliper actuated
parking brake is used, an additional lever and corkscrew is added to the existing calliper piston which is
actuated independently of the piston-driven system.