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72 Cards in this Set

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What is the maximum amt of air released in a combination vehicle when the brakes are released
less than 3lbs
What is the maximum amt of air released in a combination vehicle when the brakes are fully applied
4 lbs
What is the maximum amt of air released in a single vehicle when the brakes are released
less than 2lbs
What is the maximum amt of air released in a single vehicle when the brakes are fully applied
With dual air systems, the air pressure should build from ____ psi to ____ psi in ____ secs.
85, 100, 45
A combination vehicle air brake system should not lose air faster than:
3 psi per minute
To test your service brakes you should
Release the parking brake, move forward slowly and depress brakes
To check the slack adjusters on S Cam brakes, you should:
Wear gloves and pull hard on each slack adjuster
To test the low pressure warning signal, you should
shut off the engine
turn the electrical power off
step on and off the brake pedal to reduce air pressure
The air compressor is connected to the engine through:
Gears & V belts
The safety valve on an air compressor tank is set to open at:
150 psi
When the safety valve releases air it means that:
the pressure has exceeded 150 psi and something is wrong--get it checked by a mechanic
Parts of an air brake system
air compressor
air compressor governor
air storage tank
air tank drains
alcohol evaporator
safety valve
brake pedal
The _____ pumps air into the air storage tanks reservoirs
air compressor
The brake pedal is also called the :
foot valve or treadle pedal
pushing the pedal down harder applies more ___________
air pressure
Foundation Brakes are used on ____ wheels
The most common type of foundation brake is the ______.
S-cam drum brake
Where are brake drums located?
on each end of the vehicle's axis
Where are brake shoes and linings pushed against to stop?
insdie of the drum
How do S-cam brakes work?
you push the brake pedal which allows air into each brake chamber. Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake cam shaft. S-cam forces brake shoes away from one another and presses them against the inside of the brake drum
How do Wedge brakes work?
The brake chamber push rod pushes a wedge directly between the ends of two brake shoes.
How do disc-brakes work?
same as s-cam, but instead of the s-cam, a "power screw" is used. The pressure of the brake chamber on the slack adjuster turns the power screw. The power screw clamps the disc or rotor between the brake lining pads of a caliper
Supply pressure gauges
tell how much pressure is in the air tanks
Application pressure gauge
shows how much air pressure you are applying to the brakes
What can cause the need for increased pressure on a brake pedal?
brakes out of adjustment
air leaks
mechanical problems
Low Air Pressure Warning must come on before a tank is at what level?
before the pressure falls below 60psi

)or 1/2 the compressor governor cutout pressure on older vehicles)
What is used as a low pressure warning signal?
red light, buzzer, or wig wag
What is a wig-wag?
A deveice that drops a mechanical arm into your view when the pressue in the system drops below 60 psi
At what pressure level is it common for large buses to have a low pressure warning signal?
why were limiting valves used?
to reduce the chance of the front wheels skidding on slippery surfaces
Why are front brake limiting valves not good?
reducing the power to "slippery" reduces the stopping power of the the vehicle
under what conditions is front wheel braking good?
all conditions
What position should the front brake limiting valve be in?
normal --even in slippery conditions
What are the 2 settings for the front brake limiting valve?
normal and slippery
vehicles made before what year may have front brake limiting valves?
Autommatic front wheel limiting valves that are not controlled in the cab are overridden at ____ application pressure.
60psi or more
What brakes are considered spring brakes?
emergency brakes and parking brakes
Emergency and parking brakes must be held on by what kind of force?
mechanical force
What are springs held back by while driving?
What happens if the air pressure is removed from the spring brakes?
the springs put on the brakes
What happens if there is a leak in the air brake system that causes all the air to be lost?
the spring will put on the brakes
At what pressure range do tractor and straight truck spring brakes come on fully?
20-45 psi
What does the parking brake look like in a newer vehicle?
diamond-shaped, yellow, push-pull control know
On a parking brake which way is on and off?
NEver push the ______ down when the spring brakes are on
brake pedal
What is a modulating valve?
A control handle on the dash board used to apply the spring brakes gradually
Why do some vehicles have a separate air tank that can be used to control the spring brakes?
So you can move the vehicle in an emergency
What is a supply pressure gauge used for?
To tell you how much pressure is in the air tanks
What is a dual air brake system?
a system that has 2 separate air brake systems but a single set of brake controls
In dual air brake systems does each system have its own set of air tanks, hoses, lines ,etc
What is the primary system in a dual air brake system?
operates the regular brakes on the rear axle or axles

(and supplies air to the trailer)
What is the secondary system in a dual air brake system?
operates teh regular brakes on the front axle (and possible one rear axle)

(supplies air to the trailer)
How much pressure should the be in each section of a dual air brake system?
When do the warning light and buzzer shut off in a dual air brake system?
at a manufacutrer's set value; greater than 60 psi
If a slack adjuster moves more than _____ it probably needs adjustment
What is the most common problem found in roadside inspections?
out of adjustment brakes
Brake drums cannot have cracks longer than __ in width.
1/2 the width of the friction area on drum
When you check brake drums what are you checking for?
cracks, loose, soaked with oil or grease, or thin linings, mechanical parts in place and not broken or missing, .
Final brake checks include
low pressure warning signal
air leakage rate
spring brakes come on automatically
rate of air pressure buildup
air compressor governor cutin and out pressures
parking brakes
service brakes
How do you test the air leakage rate?
turn off engine
release service brake
time the air pressure drop
How do you test the low pressure warning signal?
shut the engine off when you have enough air pressure so that the low pressure warning signal is not on; turn on the electrical power; step on and off the brake pedal to reduce air tank pressure
How do you check that the spring brakes come on automatically?
chock the wheels,
release parking brakes
shut the engine off
step on and off the brake to reduce air tank pressure
at what pressure should the parking brake knob automatically pop out?
in single air systems pre 1975, what are the typical requirements of pressure buildup>
50-90 psi
How do you check the air compressor governor cut in cut out pressures?
run engine at a fast idle; governor should cut out at manufacturers specified pressure; air pressure on gauge will stop rising; step on and off the brake to reduce air tank presssure
What is controlled braking?
applying the brakes as hard as you can without locking the wheels
What is stab braking?
apply brakes all the way
release when lock up
when wheels roll again, apply brakes fully
how much more time does it take for air brakes to stop than hydraulic brakes?
1/2 second or more
What factors into total air brake stopping distance?
perception, reaction, brake lag, effective braking
How much distance does the air brake lag add when a truck is going 55mph
What is the total stopping distance at 55mph for an average driver under good traction and air brake conditions?
over 300ft