Ch33 Braking Fundamentals and Air
1. Technician A says heavy trucks and buses require more power to stop, than they do to accelerate. Technician B says that a doubling vehicle speed and weight requires 8x more braking force to decelerate over the same distance. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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1. Which of the following bet describes how brakes transform energy? A. Brakes convert rotational tire movement into friction. B. Brakes convert kinetic energy produced by the engine into heat. C. Brakes convert tire rotational energy into heat. D. Brakes convert vehicle kinetic energy into heat.
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10. Technician A says that right-hand S-cams are used on the right side of a vehicle and left-hand cams on the left side. Technician B says right- and left-hand S-cams can be used on either side of a vehicle. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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10. Which of the following is a reason that stroke-sensing automatic slack adjusters are almost obsolete? A. They are prone to over adjustment B. They may not adjust at all. C. They leave too much clearance between the drum and the shoes. D. They have a high failure rate.
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2. Technician A says that the latest legislative requirements for truck brake systems demand shorter stopping distances. Technician B says that, to achieve shorter stopping distances, all drum brakes are legally required to be replaced by disc brakes. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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2. Which of the following describes the relationship between braking force and vehicle speed? A. Braking force is directly proportional to vehicle speed. B. Doubling vehicle speed requires two times more braking force. C. Doubling vehicle speed requires 4x more braking force. D. Doubling vehicle speed requires 8x more braking force.
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3. How much more additional braking force is required by a vehicle weighing 40,000 lb braking from 50 mph, compared to the force required to brake when it weighs 80,000 lb.? A. The same amount of brake force is required B. 2x more braking force required C. 4x more braking force is required D. Half the braking force is required
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3. While trying to determine whether the braking force is balanced between two axles of a tractor using an infra-red thermometer, Technician A says that a hotter brake drum indicates a wheel end with increased brake torque. Technician B says that a wheel end with a cooler drum has more brake application force. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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4. How does inertia affect the operation of brakes on a tandem-axle trailer? A. More braking torque is required by the rear axle because inertia transfers weight to the rear axle. B. Wheels can lockup easier on forward axles because load and traction on the forward axle tires increases, compared to the rear axle. C. More braking is done by forward axle, compared to the rear axle. D. Less brake torque is needed by forward axles, compared to rearward axles.
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4. While recommending repairs to a truck with oil-contaminated brake lining cause by a leaking wheel seal, Technician A says the lining should be replaced, not just cleaned, on the contaminated wheel end. Technician B says that the brake lining should be replaced on both sides of the same axle with the contaminated lining. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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5. While examining a set of brake linings that were glazed, Technician A said that the cause could be the use of a replacement slack adjuster with an arm that was too long. Technician B says the cause was likely a slack adjuster that was over tightening and allowing the brakes to drag. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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5. Which of the following statements is correct? A. A left-hand S-cam camshaft turns clockwise to apply brakes. B. A left-hand S-cam camshaft turns counterclockwise to apply brakes. C. A right-hand S-cam shaft turns counter-clockwise to apply brakes. D. A right-hand S-cam shaft turns clockwise to release brakes.
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6. Consider a bus with air brakes operating at 5280 ft altitude. What effect does the lower atmospheric pressure have on the brake system operation? A. Maximum air tank pressure is lower B. Brake application force is lowered. C. There is no change on air system pressure or application force D. The transmission speed of air through brake lines is reduced.
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6. Technician A and B were estimating the cost of parts and labor to provide a quote for a brake job on a tandem-axle dump truck. Technician A says that if the truck uses outboard drums, wheel seals and brake drum hardware, such as nuts, bolts, and washers, do not need to be replaced. Technician B says that if the truck uses inboard drums, the cost for replacing hub seals and drum hardware needs to be included in the quote. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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7. Technician A says air brake systems are better than hydraulic in tractor trailer applications because it is easier to connect and disconnect tractors from trailers. Technician B says that air brake systems respond more slowly to driver input from the brake pedal, compared to hydraulic brakes. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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7. What is the effect on the brake application force if an automatic slack adjuster with a longer arm is installed? A. Application force increases, and brake chamber stroke length remains the same. B. Application force decreases, but brake stroke length increases. C. Application force increases, but brake stroke length decreases. D. Application force increases, and brake stroke length increases.
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8. Technician A says that slack adjusters do not have more than a 90-degree angle when correctly adjuted to 1/2" stroke length. Technician B says that a slack adjuster with a stroke indicator should not allow the clevis pin to travel further than the first of two pins of stroke indicator, which is closest to the brake chamber. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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8. Which of the following explains why excess heat in brake foundations causes brake fade? A. Increased drum-to-brake lining clearances increases brake chamber stroke length. B. Brake block and lining coefficient of friction increases as friction material becomes stickier. C. Heated air in brake chambers becomes thinner and more compressible. D. A fade factor caused by heat is designed into brake friction materials.
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9. Technician A says air disc brakes don't create as much brake fade as drum brakes because brake pads squeeze a rotor. Technician B says that disc brakes experience as much or more heat fade due to increased friction and shorter stopping distance standards. Who is correct? A. Technician A B. Technician B C. Both Technician A and Technician B D. Neither Technician A nor Technician B
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9. Which of the following describes braking from a brake chamber containing a power spring? A. A spring released and air-released parking brake. B. A spring applied and air-released parking brake. C. A spring released and air-applied service brake. D. A spring applied and air-released service brake.
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Release bolt
A bolt that compresses the power spring of spring brakes and releases the park brake.
Self-energization
A braking effect that causes the shoe-drum friction to rotate the brake shoe into the drum with more force.
Cam-opposite
A cam brake where the cam rotates opposite the drum's rotation to energize the brakes.
S-cam
A camshaft used to force brake shoes against the brake drum.
Glazing
A cause of brake fade characterized by a hard, glassy, burnt appearance to the lining surface, diminishing its CoF.
Edge code
A code representing the CoF of a brake lining and its composition.
Floating caliper
A disc brake caliper that is both supported and slides along on two pins.
Manual slack adjusters
A manually adjusted lever between the brake chamber and the S-cam; to maintain brake shoe to drum clearance.
Slack adjuster
A mechanical lever between the brake chamber and the foundation brake assembly.
Stroke-sensing ASA
A slack adjuster that adjusts shoe to drum clearance based on the slack adjuster stroke length.
Clearance-sensing ASA
A type of automatic slack adjuster that reduces pushrod travel based on torque input to the ASA.
Water fade
A type of brake fade that occurs when water gets between the friction surfaces and the drum that acts as a lubricant and reduces braking efficiency.
Chemical fade
A type of brake fade that takes place when steam or gases from vaporized lining materials, form between hot lining and the drum, reducing the coefficient
Roto-chambers
Actuators with a unique diaphragm and piston construction that delivers consistent output force, regardless of the pushrod position.
brake chambers are
Air operated diaphragm chambers used to apply pressure to the brakes.
Cam brakes
An "S" shaped shaft head that twists between two rollers to expand a set of brake shoes.
Cam-same
An arrangement where the cam rotates the same direction the drum's rotation to energize the brakes.
Anti-fade
An opposite condition of heat fade where the coefficient of friction increases as the brakes get hotter.
Automatic slack adjuster (ASAs)
Automatically adjust brake stroke to maintain the correct shoe-to-drum clearance.
As a vehicle brakes, its weight shifts from
Back to front. Brakes must be designed to be able to handle this inertia shift.
Long stroke chambers
Brake chambers manufactured with a 3" maximum stroke travel.
Cast drums
Brake drums made from cast iron
Centrifuge drums
Brake drums made with a cast-iron core surrounded by a steel band.
Non-asbestos organic (NAO) lining
Brake friction material commonly used in line-haul tractors where far less braking takes place.
Semi-metallic lining
Brake friction material comprising heat-resistant semi-metallic blends that are used for higher temperatures and severe service ratings.
Brake lining
Brake friction material is a 1/2" (13 mm) thick.
Brake block
Brake friction material that is 0.75" thick.
Spring brake
Brakes commonly used on rear drive axles that contain power springs that are used to apply park brakes. They are also referred to as "maxi-brakes."
Wedge brakes
Brakes that use a wedge pushed between two rollers as a lever to apply the brakes.
Right-hand camshafts
Camshafts that rotate in a clockwise direction to apply the brakes.
Air brake systems are very versatile and can be easily
Connected to trailers, plus there is no worry of leaks or spills, as in hydraulic systems.
To stop a vehicle, the kinetic energy must be
Converted into heat energy through the braking system.
Weight and speed have
Different effects on braking requirements; doubling the weight requires double the braking force but doubling the weight and the speed requires eight times the braking force.
Brake friction material is edge-coded to
Ensure the material usd is matched to the vehicle.
Air brake systems are subject to
Federal regulation under the Federal Motor Vehicle Safety Standard 121.
A moving vehicle
Has a tremendous amount of kinetic energy.
Slack adjusters are used to
Keep the brake chamber stroke adjusted; all modern vehicles are equipped with automatic slack adjusters.
S-cam used in cam brakes can be
Left or right handed.
Mechanical fade
Loss of brake effectiveness that occurs when drums expand due to heat.
Actuators have dual chambers with
One containing a power spring to operate the emergency or parking brake system.
All brake systems are dual-brake systems, meaning that if
One system fails the other can still stop the vehicle.
Federal Motor Vehicle Safety Standard 121 (FMVSS 121)
Performance and safety standards legislation for air brakes.
Left-hand camshafts
S-cams that rotate in a counter-clockwise direction to apply the brakes.
Air brake systems can handle
Small system leaks without adverse effects.
Power springs
Springs in brake actuators used to apply park brakes or internal pushrod lock mechanisms.
Coefficient of friction (CoF)
The amount of friction between two objects in contact; calculated by dividing the force required to move the object by the weight of the object.
Brake foundation
The braking components found at the wheel ends.
Kinetic energy
The energy of a body in motion
Brake torque
The force applied to the foundation brakes during braking.
Brake fade
The inability of the bake to maintain its effectiveness. Brake fade causes a need for increased pedal application force to maintain the same braking effectiveness.
Heat fade
The loss or reduction in the CoF as the brake temperature increases.
Because of their simplicity, cam brakes are
The most popular air brake foundation brake system in on-highway trucks.
Compressed air is
The primary method of choice to multiply brake force for highway trucks.
AL factor
The size or surface area of a brake chamber multiplied by the length of the slack adjuster in inches.
Spring brake chambers must be disarmed before
They are discarded by cutting the power spring with an acetylene torch.
Brake chamber size and slack adjuster lever length combine
To deliver a twisting force to the brake camshafts.
All brake systems use some force
To multiply the braking effort applied to the brake pedal by the driver. This force can be compressed air, hydraulic pressure, or a combination of the two.
To operate, brakes must
Turn kinetic energy into heat, but they must also be capable of dissipating the heat quickly, or they quickly lose their effectiveness.
Inertia shift
Weight that moves front he rear of the vehicle to the front during braking.
