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72 Cards in this Set
- Front
- Back
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What is the maximum amt of air released in a combination vehicle when the brakes are released
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less than 3lbs
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What is the maximum amt of air released in a combination vehicle when the brakes are fully applied
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4 lbs
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What is the maximum amt of air released in a single vehicle when the brakes are released
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less than 2lbs
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What is the maximum amt of air released in a single vehicle when the brakes are fully applied
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3lbs
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With dual air systems, the air pressure should build from ____ psi to ____ psi in ____ secs.
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85, 100, 45
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A combination vehicle air brake system should not lose air faster than:
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3 psi per minute
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To test your service brakes you should
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Release the parking brake, move forward slowly and depress brakes
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To check the slack adjusters on S Cam brakes, you should:
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Wear gloves and pull hard on each slack adjuster
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To test the low pressure warning signal, you should
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shut off the engine
turn the electrical power off step on and off the brake pedal to reduce air pressure |
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The air compressor is connected to the engine through:
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Gears & V belts
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The safety valve on an air compressor tank is set to open at:
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150 psi
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When the safety valve releases air it means that:
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the pressure has exceeded 150 psi and something is wrong--get it checked by a mechanic
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Parts of an air brake system
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air compressor
air compressor governor air storage tank air tank drains alcohol evaporator safety valve brake pedal |
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The _____ pumps air into the air storage tanks reservoirs
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air compressor
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The brake pedal is also called the :
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foot valve or treadle pedal
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pushing the pedal down harder applies more ___________
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air pressure
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Foundation Brakes are used on ____ wheels
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each
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The most common type of foundation brake is the ______.
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S-cam drum brake
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Where are brake drums located?
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on each end of the vehicle's axis
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Where are brake shoes and linings pushed against to stop?
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insdie of the drum
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How do S-cam brakes work?
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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
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How do Wedge brakes work?
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The brake chamber push rod pushes a wedge directly between the ends of two brake shoes.
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How do disc-brakes work?
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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
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Supply pressure gauges
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tell how much pressure is in the air tanks
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Application pressure gauge
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shows how much air pressure you are applying to the brakes
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What can cause the need for increased pressure on a brake pedal?
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brakes out of adjustment
air leaks mechanical problems |
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Low Air Pressure Warning must come on before a tank is at what level?
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before the pressure falls below 60psi
)or 1/2 the compressor governor cutout pressure on older vehicles) |
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What is used as a low pressure warning signal?
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red light, buzzer, or wig wag
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What is a wig-wag?
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A deveice that drops a mechanical arm into your view when the pressue in the system drops below 60 psi
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At what pressure level is it common for large buses to have a low pressure warning signal?
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80-85
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why were limiting valves used?
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to reduce the chance of the front wheels skidding on slippery surfaces
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Why are front brake limiting valves not good?
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reducing the power to "slippery" reduces the stopping power of the the vehicle
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under what conditions is front wheel braking good?
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all conditions
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What position should the front brake limiting valve be in?
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normal --even in slippery conditions
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What are the 2 settings for the front brake limiting valve?
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normal and slippery
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vehicles made before what year may have front brake limiting valves?
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1975
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Autommatic front wheel limiting valves that are not controlled in the cab are overridden at ____ application pressure.
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60psi or more
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What brakes are considered spring brakes?
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emergency brakes and parking brakes
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Emergency and parking brakes must be held on by what kind of force?
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mechanical force
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What are springs held back by while driving?
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air
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What happens if the air pressure is removed from the spring brakes?
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the springs put on the brakes
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What happens if there is a leak in the air brake system that causes all the air to be lost?
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the spring will put on the brakes
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At what pressure range do tractor and straight truck spring brakes come on fully?
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20-45 psi
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What does the parking brake look like in a newer vehicle?
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diamond-shaped, yellow, push-pull control know
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On a parking brake which way is on and off?
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pull=on
push=off |
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NEver push the ______ down when the spring brakes are on
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brake pedal
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What is a modulating valve?
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A control handle on the dash board used to apply the spring brakes gradually
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Why do some vehicles have a separate air tank that can be used to control the spring brakes?
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So you can move the vehicle in an emergency
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What is a supply pressure gauge used for?
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To tell you how much pressure is in the air tanks
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What is a dual air brake system?
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a system that has 2 separate air brake systems but a single set of brake controls
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In dual air brake systems does each system have its own set of air tanks, hoses, lines ,etc
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YES
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What is the primary system in a dual air brake system?
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operates the regular brakes on the rear axle or axles
(and supplies air to the trailer) |
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What is the secondary system in a dual air brake system?
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operates teh regular brakes on the front axle (and possible one rear axle)
(supplies air to the trailer) |
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How much pressure should the be in each section of a dual air brake system?
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100psi
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When do the warning light and buzzer shut off in a dual air brake system?
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at a manufacutrer's set value; greater than 60 psi
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If a slack adjuster moves more than _____ it probably needs adjustment
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1inch
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What is the most common problem found in roadside inspections?
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out of adjustment brakes
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Brake drums cannot have cracks longer than __ in width.
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1/2 the width of the friction area on drum
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When you check brake drums what are you checking for?
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cracks, loose, soaked with oil or grease, or thin linings, mechanical parts in place and not broken or missing, .
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Final brake checks include
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testing:
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 |
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How do you test the air leakage rate?
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turn off engine
release service brake time the air pressure drop |
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How do you test the low pressure warning signal?
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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
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How do you check that the spring brakes come on automatically?
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chock the wheels,
release parking brakes shut the engine off step on and off the brake to reduce air tank pressure |
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at what pressure should the parking brake knob automatically pop out?
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20-40psi
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in single air systems pre 1975, what are the typical requirements of pressure buildup>
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50-90 psi
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How do you check the air compressor governor cut in cut out pressures?
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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
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What is controlled braking?
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applying the brakes as hard as you can without locking the wheels
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What is stab braking?
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apply brakes all the way
release when lock up when wheels roll again, apply brakes fully |
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how much more time does it take for air brakes to stop than hydraulic brakes?
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1/2 second or more
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What factors into total air brake stopping distance?
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perception, reaction, brake lag, effective braking
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How much distance does the air brake lag add when a truck is going 55mph
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32ft
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What is the total stopping distance at 55mph for an average driver under good traction and air brake conditions?
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over 300ft
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