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70 Cards in this Set
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- Back
1. An air leak at point ‘X’ in the system shown above would cause which of these to leak down? A. #1 tank only B. #2 tank only C. #2 and #4 tanks only D. the entire system |
The correct answer is A. If you look closely at the diagram, you will notice two check-valves at tanks 2 and 3. An air leak at the point indicated would be isolated to tank 1 only; therefore only tank 1 would lose air pressure in the circuit. |
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2. The slack adjuster shown above is being adjusted. Technician A says that travel ‘X’ should be as short as possible without dragging the brakes.Technician B says that angle ‘Y’ should be less than 90-degrees when the brakes are applied. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is A. With the chamber pushrod fully extended (brakes applied), the properly set adjuster forms a 90-degree angle with the pushrod. Technician B is incorrect because an angle of less. than 90 degrees would indicate improper adjustment. Dimension X should be as short as possible to allow for maximum stroke during braking. |
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3. Which of the following cannot cause a drum on an air-braked vehicle to overheat? A. an over-tightened brake adjuster at that wheel B. under-adjusted brake(s) elsewhere on the vehicle C. too-high governor cut-out pressure D. driving downhill in too high a gear |
The correct answer is C. The governor controls the air compressor output by unloading or cycling it. It has no direct effect on the mechanical brake parts. While the pressure setting is important to maintain air brake system pressure within acceptable limits, an incorrect setting will not cause the drum on an air-braked vehicle to overheat. All other choices given, however, will cause overheating problems. |
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4. All the brakes drag on a truck with hydraulic brakes. Which of the following could be the cause? A. air in the hydraulic system B. too high a vacuum supply to the power brake booster C. a leaking secondary cup in the master cylinder D. no brake pedal free travel |
The correct answer is D. Only a brake pedal with no free travel will cause all of the brakes to drag. Answer A-air in the hydraulic system, will cause a spongy pedal, while answer B-too high a vacuum to the power booster, won’t affect brake drag at all. Answer C, a leaking secondary cup in the master cylinder, could increase pedal travel, but won’t cause the brakes to drag. |
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5. Which of the following could cause a pulsating brake pedal on a truck with hydraulic brakes? A. zero brake pedal free travel B. glazed linings C. an out-of-round brake drum . D. a frozen wheel cylinder piston |
The correct answer is C. Of the choices given, only an out-of-round brake drum can cause pulsation in a hydraulic brake system. Answer A, zero brake pedal free travel, will cause a dragging brake condition, but not pulsation. Answer B, glazed linings, will affect stopping performance and noise, and answer D, a frozen wheel cylinder, will degrade stopping performance, but will not cause pulsation |
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6. In the ‘AL’ factor, the ‘L’ refers to the: A. lining’s friction code B. thickness of the lining C. type of front-brake limiting valve D. length of the slack adjuster |
The correct answer is D. The brake adjuster’s length (L) and the brake Chamber’s size (A) are two variables commonly altered to meet braking requirements. The product of these two values is expressed as the ‘AL’ factor. This factor, when multiplied by 60 psi air pressure, is the industry standard for braking calculations. |
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7. Technician A says that linings worn too thin on an air-braked vehicle can cause the S-camshaft to roll over. Technician B says this condition can cause excess brake pedal travel. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is A. The brake adjuster is connected to a shaft that runs perpendicular to the plane formed by the pushrod and slack adjuster. As the pushrod is extended, the shaft rotates. The shaft, in turn, is connected to an S-shaped cam between the brake shoes. As the shaft rotates, so does the cam. The brake shoes are forced apart and against the brake drum, creating the friction needed to slow the vehicle. Thin brake linings can allow the S-cam to roll over, but will not affect brake pedal travel. |
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8. Spring brakes on an air-braked vehicle must be able to hold the vehicle facing uphill or downhill on what percent grade? A. 10% B. 20% C. 30% D. 40% |
The correct answer is B. Per Federal Motor Vehicle Safety Standard (FMVSS) 121, the parking brakes must be able to hold a vehicle, loaded to its gross weight rating, stationary on a smooth, dry, concrete roadway, facing uphill or downhill on a 20% grade. In the emergency mode, the parking brakes must be able to exert a retarding force equal to 28% of the gross axle rating. |
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9. The driver of a truck with hydraulic brakes says the pedal reserve is too low. Technician A says the brakes could be out-of adjustment. Technician B says one brake system may have failed. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technicians are right. Either condition will cause the driver to notice a low pedal reserve.
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10. The parking brakes fail to apply on a truck with air. brakes. Technician A says this could be caused by low air pressure in the spring brake chamber. Technician B says this could be caused by a ruptured spring brake diaphragm. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is D, neither technician is right. In addition to applying the service brakes used in everyday driving, the brake chambers on the rear tractor axles and on the trailer axles apply the parking brakes. These brake chambers (spring brakes) incorporate a second chamber containing a second diaphragm and a powerful spring. When the vehicle is in use, air pressure supplied to the spring diaphragm compresses the spring and the parking brakes are held off. When the vehicle is parked, the dash valves are pulled out. This exhausts spring brake hold-off air, allowing the spring to apply the parking brakes. Neither low air pressure in the spring brake chamber nor a ruptured diaphragm can prevent the parking brake from being applied. |
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11. How much free movement should exist between a slack adjuster and its camshaft? A. 0.005-in. max. B. 0.010-in. max. C. 0.015-in. max. D. 0.020-in. max. |
The correct answer is D. Excessive wear allows lost motion between the slack adjuster and camshaft. Replace the camshaft and/or slack if there is more than .020-in. free movement between slack and camshaft. The clearance between the slack clevis pin and its bushing should also not exceed .020-in. |
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12. The warning light on a truck with an anti-lock brake system lights when the truck is started. When the truck is moving, the light stays on. Which of the following could be the cause? A. misadjusted wheel sensor B. bad air release solenoid C. blown fail-safe monitor fuse D. bad warning light relay |
The correct answer is A. When a vehicle equipped With ABS is started, the system checks itself by cycling all valves and illuminating dash- mounted indicator lights. If everything checks OK, the lights go out once the vehicle starts rolling. In the event of a fault, one indicator light stays on, and the affected part of the system reverts to conventional brake system operation. A specialized tester is then used to pinpoint the problem. In this case, however, the only possible cause would be a misadjusted wheel sensor, because the blown fuse (answer C) or bad relay (answer D) wouldn’t allow the warning light to illuminate at all, and answer B, a bad air release solenoid wouldn’t be detected since it’s not wired into the electronic diagnostic system. |
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13. The driver of a truck with air brakes says it has poor stopping power. Any of these could be the cause EXCEPT: A. The quick release valve exhaust port is plugged. B. The air pressure is too low. C. The service line is restricted. D. The brakes are adjusted incorrectly. |
The correct answer is A. The quick release valve operates to release the brakes; all other choices indicate functions that serve to apply the brakes. Low air pressure, a restricted service line or misadjusted brakes can cause poor stopping power. |
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14. Technician A says brake shoe oil contamination should be no more than 10% of the lining surface. Technician B says oil contamination can lead to brake imbalance. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technicians are right. If the lining is otherwise OK, but an area no larger than 10% of the total lining area is contaminated by grease or oil, the spot can be cleaned with brake cleaning solvent (not gasoline or another substitute). However, this isn’t the safest option, as it could lead to a brake imbalance condition if done improperly. |
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15. The driver of a truck with air brakes says that the brakes are slow to release. Which of the following is the LEAST likely cause? A. weak return springs B. a plugged exhaust port C. a kinked air line D. worn brake linings |
The correct answer is D. Of the choices given, only worn brake linings would not cause slow brake release. Weak return springs, a plugged exhaust port or a kinked air line all could result in a slow brake release condition. |
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16. An air-braked vehicle has lining wear tapered from inboard to outboard. There also is abrasion on the outer edges of the brake shoes. What could NOT be the cause? A. worn anchor pins B. worn outer S-cam bushings C. distorted anchor pin holes D. weak return springs |
The correct answer is D. Lining wear should be even around the circumference of the brake assembly, and from inboard to outboard. More wear on the bottom, top or one side could indicate that peripheral brake hardware is worn. Worn anchor pins, holes and bushings, or outer S-cam bushings can allow applied force to push the shoes to one side, resulting in tapered lining wear. This condition often is accompanied by outer-edge abrasion on the shoes, caused by the shoes tracking out of alignment due to worn parts. |
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17. The low pressure warning light or buzzer activates at what pressure? A. 60 psi B. 70 psi C. 50 psi D. 40 psi |
The correct answer is A. The low pressure warning indicator is installed on the primary reservoir, and notifies the operator of system air depletion by sounding a warning buzzer, and in some cases, illuminating a light on the instrument panel, when pressure drops to approximately 60 psi. |
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18. Normal governor cut-in pressure is set to what pressure? A. 150 psi B. 175 psi C. 125 psi D. 100 psi |
The correct answer is D. On a typical system, when the air pressure in the supply reservoir falls below 100 psi, the governor ‘cuts in’ and signals the compressor to deliver air to the reservoirs. The governor regulates the air compressor’s output and keeps it from over-supplying the system with an excessive amount of air pressure. |
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19. When should the air tanks be drained on an air-braked vehicle with no air dryer. A. once a month B. once a week C. once a day D. never
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The correct answer is C. Manual valves should be drained on a daily basis, especially inhumid or wet climates where excessive amounts of moisture are present. Drain valves are installed in each reservoir to help purge the system from its worst enemy, moisture. |
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20. Technician A says that low volume compressors are needed for applications such as trucks with multiple trailers. Technician B says that air compressors are available with up to four cylinders. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
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The correct answer is B. A single-cylinder or two-cylinder compressor is used for most truck applications. However, three-and four-cylinder air compressors are available for applications where high air volume is in demand, such as on trucks with multiple trailers and air-powered accessories. |
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21. A technician has discovered oil in the brake reservoirs. Which of the following could be the cause? A. a clogged compressor air filter B. a leaking wheel seal C. a defective air tank pop off valve D. an incorrectly adjusted governor |
The correct answer is A. In addition to a slow air compressor build-up time, a clogged filter creates a vacuum in the compressor cylinder during the intake stroke. Oil is then sucked past the compressor’s piston rings. On the compression stroke, the pis- ton pumps all of the accumulated oil through the discharge line, and right into the air system. Oil in the air system can gum up major components, causing them to fail prematurely. |
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22. A technician is rebuilding an air compressor. Before removing the connecting rod bolts, the technician should: A. lubricate the bearing caps and connecting rods B. mark the bearing caps and connecting rods C. check the cylinder walls for damage D. none of the above |
The correct answer is B. Before the connecting rod bolts are removed, each connecting rod and hearing cap must be marked. The connecting rod and its corresponding cap must be matched together upon reassembly. |
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23. Technician A says an air dryer has two cycles, charge and purge. Technician B says an air dryer collects moisture and contaminants before they get into the brake system. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technicians are right. The air dryer removes moisture and contaminants from the air system before the compressed air travels to the primary reservoir. The air dryer operates in two cycles, charge and purge. The charge cycle accepts compressed air, sometimes contaminated with moisture or debris, from the air compressor. Compressed air travels through an oil separator where oil and solid contaminants are removed. Water, and water vapor are removed from the air by way of desiccant material. The air then enters the primary tank through a one-way check valve. Once the governor cut-out pressure is achieved, the gover- nor signals the air dryer to begin the purge cycle. This signal opens the purge port of the air dryer to allow contaminants to exit through to the atmosphere. The valve stays Open until the governor cut-in pressure is achieved, signaling the compressor to once again build air pressure. |
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24. The driver of an air-braked truck with ABS complains that on a panic stop in wet weather conditions, the truck’s right rear wheel locks up. What could be the cause? A. a defective ABS/ECU B. an air leak in the primary reservoir C. a defective ABS wheel sensor D. a defective diagnostic switch |
The correct answer is C. Each sensor/wheel combination is a kind of electric generator consisting of a permanent magnet and coil. As the rotating teeth pass a sensor, the magnetic flux picked up by the coil is intermittently altered. Alternating voltage is produced, the strength and frequency of which are proportional to wheel speed. Wheel speed data is sent to an Electronic Control Unit (ECU), which sends an electrical signal to solenoid valves that reduce air pressure to the brake chamber(s) at the affected wheel(s). The new rate of deceleration is recognized by the ECU, which signals the solenoid valves to restore air pressure. This loop occurs repeatedly, as long as the deceleration rate approaches lock-up. |
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25. The driver of an air-braked truck complains that when he takes his foot off of the brake pedal to accelerate after a stop, the brakes do not release right away. What could be the cause? A. a defective pop off valve B. a defective quick release valve C. a defective tractor protection valve D. none of the above |
The correct answer is B. After a stop, when the driver lifts his foot from the brake pedal, a quick release valve allows brake actuation air to be quickly exhausted near the brakes it serves, rather than having to travel back through the supply line, thus speeding brake release time. |
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26. What is the minimum allowable measurement for scoring of a brake drum?A. 0.020 B. 0.010 C. 0.10 D. 0.21 |
The correct answer is B. Light scoring should be no deeper than 0.010-in. It is permissible to resurface a drum to 0.060-in. oversize, but bear in mind that the radius of the new lining will not match that of the drum. Reduced braking performance and lin- ing damage can result. |
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27. Technician A says that a trailer control valve can be used to stop a moving combination vehicle. Technician B says that a trailer control valve is Used to check the integrity of a fifth wheel connection. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is B. The primary function of the trailer control valve is to allow the operator to check the fifth wheel connection by attempting to move the coupled vehicle with the trailer brakes applied. Because of its graduated application, some drivers use the trailer control valve by applying it while the combination is in motion to save wear and tear on the tractor brakes. This practice is not recommended and is in some cases hazardous, Causing trailer sway while driving, and contributing to accelerated wear of the trailer brakes. |
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28. A relay valve on trailer air brakes with too high of a crack pressure can cause: A. excessive brake wear B. premature brake application C. delayed brake application D. wheel lock-up |
The correct answer is C. Crack pressure that is too high can cause delayed application, insufficient braking and trailer piishing, if the affected axle is on the trailer. |
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29. Technician A says the minimum thickness of solid disc brake rotors should be at least 0.779-in. Technician B says the minimum thickness of vented disc brake rotors should be at least 1.626-in. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is. C, both Technicians are right. When measuring the thickness of a disc brake rotor with a micrometer, the minimum thickness of a solid rotor must be at least 0.779-in. The minimum thickness of vented rotors must be at least 1.626-in. |
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30. What causes the condition of ‘brake fade? A. brake linings get too hot B. hydraulic fluid contamination C. oil in the air system D. an air leak at the supply reservoir |
The correct answer is A. Brake fade is a condition of brake lining overheating. When fade occurs, lining-to-drum friction is reduced and vehicle stopping distance is increased. Different linings have different fade characteristics. Therefore, if mismatched linings are installed on different axles, brake action and balance are affected. |
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31. The driver of a tractor/trailer combination with air brakes says that an air leak in the trailer system is causing the tractor brakes to lock up. Which of the following could be the cause? A. defective governor B. defective tractor protection valve C. clogged air compressor filter D. worn brake linings |
The correct answer is B. A tractor protection valve senses pressure in one or both lines that carry air to the trailer. These lines are connected to the trailer by means of quick-connect air fittings called ‘gladhands.’ When there is no pressure in the line(s) 'due to trailer break-away or a gross air leak in the trailer circuit, the valve closes to maintain air pres- sure in the tractor circuit. In everyday use, the valve also works in conjunction with the dash-mounted trailer parking brake valve to shut off air to the trailer circuit before disconnecting the tractor from the trailer. |
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32. The driver of a truck with hydraulic drum brakes complains that when his vehicle is unloaded, the rear brakes lock up on moderate to hard braking application. Which of the following could be the cause?A. defective metering valve B. leaking brake line C. defective proportioning valve D. brakes out of adjustment |
The correct answer is C. A defective or leaking load proportioning valve will cause rear brake lock- up during moderate to hard brake application, brake drag, grabbing, and premature rear brake wear. |
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33. Technician A saysthat Automatic Traction Control (ATC) controls the engine only. Technician B says that automatic traction control works in tandem with anti-lock brakes. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is B. The ATC system works in tandem with the ABS system, utilizing wheel speed sensors and the ABS modulator. It consists of an ATC valve and an engine data transfer link to achieve traction control. The ATC system will activate engine and/or brake control when the electronic control unit senses that the rotation of the driven wheels is higher than that of the non-driven |
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34. Proper voltage for an anti-lock brake system to function properly must be: A. 8.5 to 13 volts B: 12.0 to 18 volts C. 24.0-to 27 volts D. 9 5 to 14 volts |
The correct answer is D. Voltage must be between 9.5 and 14 volts for the system to function properly. To check voltage, turn the ignition on and connect a volt/ohmmeter to the proper pins in the electronic control unit. Consult the manufacturer’s service manual for the specific pin locations. |
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35. The driver of a truck with hydraulic power brakes complains of a hard brake pedal and poor stopping. Which of the following could be the cause? A. leaking master cylinder B. defective power brake booster C. defective proportioning valve D. leaking wheel cylinder |
The correct answer is B. A defective brake booster would not perform the assist function, causing a hard brake pedal. When the brake pedal is pushed, atmospheric pressure is introduced into the chamber on the firewall side of the brake booster diaphragm. This action causes a pressure differential, forcing the booster power piston forward, actuating the master cylinder. |
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36. On a truck with air brakes, the air tank pop off valve releases air prematurely. A technician has removed and checked the valve and it has checked out OK. What else could cause this problem? A. governor adjustment B. kinked air hose C. defective drain valve D. defective pressure limiting valve |
The correct answer is D. The pressure limiting (or proportioning) valve reduces pressure to components that do not necessarily need full system pressure such as air suspensions, tank vents and drains. |
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37. The minimum suggested lining thickness for drum brakes is: A. 1/2-in. B. 1/4-in C. 3/4-in. D. 1/3-in. |
The correct answer is B. Replace the linings if unusually patterned cracks are found and the lining measures less than 1/4.-in. at its lowest point. |
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38. Technician A says that some compressor governors are adjustable. Technician B says that some governors are mounted in the engine compartment instead of on the compressor. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technicians are right. The governor may be attached to the compressor or externally mounted in the engine compartment with a line connected to it from the compressor. The governor is adjustable if an adjustment screw is present, and the cover is not marked non-adjustable. Take caution not to over adjust the gover- nor. Each 1/4 turn of the adjustment screw can raise or lower the pressure settings approximately 4 psi. |
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39. Technician A says that when both knobs on a dualcircuit push-pull valve are pushed in, air is supplied to the tractor only. Technician B says that both knobs are pushed in to apply the parking brakes. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is D, neither Technician is right. The dual unit controls the parking brakes on the tractor and the air supply on the trailer. When both valves are in, air is supplied to the tractor and trailer spring brake chambers to release the parking brakes. |
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40. The driver of a truck with hydraulic disc/drum brakes says the truck dives when the brakes are applied. Which of the following could be the cause? A. defective metering valve B. defective proportioning valve C. defective safety valve D. defective check valve |
The correct answer is A. A brake metering valve is used on front disc/rear drum brake systems for the purpose of providing simultaneous application of all brakes. The valve is located in the front brake hydraulic circuit, and delays front brake operation until the rear brakes begin to operate. When the rear brakes make contact with the drums, hydraulic pressure in the front circuit will open the metering valve, sending pressurized fluid to the front brakes.
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41. A technician finds that during periods of low vacuum, a truck with hydraulic power brakes experiences a hard pedal when stopping. Which of the following could be the cause? A. defective one-way check valve B. leaking master cylinder C. improperly adjusted brakes D. crimped brake line |
The correct answer is A. The one-way check valve is designed to maintain brake assist during periods of low vacuum. The booster is connected to intake manifold vacuum on gasoline engines, or to a vacuum pump on diesel engines, by way of a vacuum hose and one-way check valve.
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42. A truck with hydraulic brakes has developed a leak in the primary system, and the brake warning light is illuminated. What is the name of the switch that activates the dash light? A. warning differential switch B. metering differential switch C. backup relay switch D. pressure differential switch |
The correct answer is D. The pressure differential warning switch illuminates a warning light to alert the driver of pressure loss in one of the hydraulic circuits. Under normal operating conditions, the hydraulic pressure on both sides of the pressure differential piston is balanced and the piston is centered. In this position, a spring-loaded plunger opens the contacts and keeps the brake warning light off. If one of the circuits develops a leak, the higher pressure in the other circuit will move the piston to one side. This causes the pressure differential switch to close, completing the circuit and illuminating the brake warning light.
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43. Which of the following is NOT the name for a type of driveline parking brake? A. expanding disc B. contracting shoe C. expanding shoe D. disc |
The correct answer is A. The correct names of the different types of driveline parking brakes are Contracting Shoe, which squeezes the outer portion of the driveline parking brake drum, Expanding Shoe, which expands into the driveline parking brake drum, and Disc, which squeezes a disc brakerotor assembly in order for the parking brakes to hold. |
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44. A driver complains of pulling to one side when the brakes are applied. A technician has physically .checked the brakes and has found the system to be operating properly. What else should the technician check? A. axle seal leakage B. wheel bearing adjustment C. vehicle height D. coefficient of friction |
The correct answer is B. In addition to malfunctioning brake system parts, worn out hubs and wheel bearings can also contribute to poor braking performance. Many apparent braking problems that persist after all the worn brake parts have been replaced can actually be caused by wheel bearings being worn out or misadjusted. |
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45. technician says that DOT 3 brake fluid has a higher boiling point that DOT 4 brake fluid. Technician B says that DOT 5 brake fluid should not be used in a vehicle with ABS. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is B. Since DOT 5 brake fluid is silicone based, it’s prone to aeration. This means that When the fluid is agitated, tiny air bubbles, like those found in a carbonated drink, form in the fluid. For this reason, DOT 5 brake fluid should never be used in an anti-lock brake system. The boiling point of DOT 3 is lower (401°F) than that of DOT 4 brake fluid (446°F). |
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46. Technician A says that before a gear-driven air compressor is replaced, the gear must be timed with the engine prior to installation. Technician B says that when timing an air compressor gear, the piston in the engine’s No. 1 cylinder must be at Top Dead Center. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technicians are right. If the compressor is gear-driven, the drive gear must be meshed With the timing gear on the engine prior to installation. A misaligned compressor drive gear can cause poor compressor air build-up. On most engines, compressor timing is achieved by aligning the timing marks on the compressor drive gear and crankcase. The piston in the engine’s No. 1 cylinder must be brought to Top Dead Center (TDC), and the air compressor drive gear must be aligned. |
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47. A technician finds that an air-braked truck’s service brakes grab or pull to one side when stopping. Which of the following could be the cause? A. glazed or contaminated lining B. insufficient air pressure C. overloaded vehicle D. defective quick-release valve |
The correct answer is A. Glazed or contami- nated linings would cause the vehicle to pull to one side when braking, especially on the front axle. The lining should also be checked for foreign material that may be imbedded. If linings are contaminated with oil or grease, correct the cause before relining. The problem is almost always a leaking oil seal, too much grease on a grease-type wheel hearing or camshaft bushing, or the result of careless handling. |
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48. Technician A says that when adjusting a manual slack adjuster, if there is little or no pressure on the wrench once the shoes make contact with the drum, the adjustment mechanism is broken and the slack . adjuster should be replaced. Technician B says if the adjustment mechanism is broken, the slack adjuster can be rebuilt. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is A. As contact is made, resistance should be felt through the wrench. Little or no resistance as the brakes are tightened means the slack’s adjustment mechanism is broken, and the slack adjuster should be replaced. |
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49. A truck with a hydro-assist booster is experiencing a hard pedal. Which of the following could be the cause? A. low power steering pressure B. high brake fluid pressure C. high engine temperature D. leaking brake hose |
The correct answer is A. The hydro-boost system is a variation on the conventional vacuum-assist system. It operates by using the power steering pump fluid pressure instead of manifold vacuum. |
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50. When checking an application valve for internal leaks, an ultrasonic leak detector can be used at which port? A. exhaust port B. discharge port C. release port D. application port |
The correct answer is A. An ultrasonic leak detector can be used at the exhaust port to detect internal air leaks. The tool transposes the sound of an air leak, no matter how small, into a frequency that can be heard through headphones. Also, the intensity of the signal can be observed on an LCD display. In all other cases, soapy water can be used. |
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51. All of the following are phases of hydraulic brake ABS control EXCEPT: A. pressure maintain B. pressure induction C. pressure increase D. pressure decrease |
The correct answer is B. The three phases of hydraulic control that occur during an ABS stop are pressure maintain, pressure decrease, and pressure increase. Pressure maintain means that any further brake fluid pressure to the slipping Wheel or wheels is cut off. Phase two is known as the pressure decrease function. If wheel slip continues to increase in the pressure maintain phase, hydraulic pressure to the wheel(s) is then decreased until Wheel slip approached zero. This means that wheel speed equals vehicle speed. At this point the pressure maintain phase is re-engaged. The final phase is referred to as the pressure increase stage. If wheel slip approaches zero in the pressure maintain phase, hydraulic pressure to the wheel(s) is increased until wheel slip begins to occur. This means that wheel speed is less than vehicle speed. The pressure increase phase is another name for normal brake operation, since maximum master cylinder pressure is applied to the Wheels. |
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52. Technician A says that the driveline parking equalizes torque through the engine. Technician B says that the driveline parking brake is mounted on the rear of the transmission assembly. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is B. The driveline parking brake is mounted at the rear of the transmission. While the operation of these brakes varies, the basic principles are the same. The braking mechanism, mounted on the rear of the transmission or transfer case, holds the vehicle by equalizing torque through the differential. |
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53. When operating an air-braked vehicle at idle, air pressure should build from 85-100 psi in: A. 30 seconds B. 45 seconds C. 60 seconds D. 90 seconds |
The correct answer is B. With the engine running at idle, air pressure should build from 85-100 psi (pounds per square inch) within 45 seconds. If the engine is running at full-governed rpm, air should build up Within 25 seconds, and the compressor should maintain a constant pressure of 100-120 psi. |
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54. With foot pressure applied, the brake pedal on a truck with hydraulic power brakes moves down slightly when the engine is started. Technician A says that this condition can be caused by a leaking power brake booster diaphragm. Technician B says that the cause could be a faulty power brake booster check valve. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is D, neither Technician is right. With the brake pedal applied while starting the engine, the pedal should move down slightly, indicating that the vacuum booster is operating properly. |
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55. Technician A says a 4-channel ABS system independently controls all of the brakes on a 3-axle vehicle. Technician B says a 6-channel system is needed to independently control all of the brakes on a 3-axle vehicle. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is B. The number of channels in an individual-wheel control system refers to the number of individual brakes its ECU is capable of independently controlling. For example, a system that can independently accommodate all of the brakes on a steer axle and tandem is referred to as a 6-channel system. A 4-channel system can also be applied to a 3-axle vehicle, but the front and rear wheels on either side of the tandem would be braked simultaneously, rather than independently. |
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56. Hydraulic brakes that drag or fail to release can be caused by which component in the master cylinder. A. leaking primary cup B. leaking secondary cup C. failure of the residual pressure check valve D. clogged compensating port |
The correct answer is D. The compensating port allows for residual hydraulic line pressure to be discharged into the reservoir as the brake pedal is released. A clogged or restricted compensating port will create a pressure build-up, which will cause the brakes to drag or fail to release. The cup can be clogged by foreign matter, blocked by a swollen primary cup or covered by the primary cup if the master cylinder pushrod is improperly adjusted. |
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57. Technician A says that a stoplight switch on a truck with air brakes operates electro-pneumatically in tandem with a two-way check valve. Technician B says that a failure in the stoplight switch causes the trailer control valve to activate. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is A. The stoplight switch is an electro-pneumatic, non-grounded switch that operates in tandem with a two-way check valve. When the brakes are applied, the air pressure moves an internal switch that completes the circuit, light- ing the stoplights. A defective stoplight switch will not cause the trailer control valve to actuate. |
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58. All of the following names describe air brake reservoirs EXCEPT: A. primary B. secondary C. auxiliary D. supply |
The correct answer is C. The supply reservoir feeds air to the primary and secondary reservoirs of the split service system. When the brake pedal is depressed, air flows from the primary reservoir, through the primary section of the foot valve, and out to the rear foundation brakes. Meanwhile, at the same time, air flows from the secondary reservoir through the secondary section of the foot valve to actuate the front foundation brakes. |
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59. Technician A says that the pressure side of the turbocharger supplies air to the air compressor. Technician B says that air can be drawn into the compressor from the atmosphere. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technician are right. Air can be drawn into the compressor directly from the atmosphere through a filter, or from the pressure side of the engine turbocharger. When the air enters the compressor cylinder, it is compressed by the upward motion of the piston, and forced through a discharge valve to the supply reservoir. |
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60. The oil in an air compressor with its own sump. should be checked: A. once a week B. every two weeks C. once a month D. once a day |
The correct answer is D. Some air compressors utilize their own oil sumps. If the compressor is self-lubricated, the oil should be checked daily. If oil is pumped in from the engine compartment, the engine oil should be checked in accordance with the engine manufacturer’s scheduled maintenance intervals. |
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61. Technician A says the brake ABS is used to control the truck during deceleration. Technician B says ATC is used to keep loads from shifting. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is A. The Anti-lock Brake System (ABS) helps control the truck during deceleration. Automatic Traction Control (ATC) helps to control the truck during acceleration. |
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62. Technician A says automatic slack adjusters improve brake balance and reduce downtime and maintenance costs. Technician B says manual slack adjusters provide reduced chamber travel and less air consumption. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is A. Having the slack adjusters automatically adjust alleviates the need for the driver or technician to adjust them. The result is reduced down time and less maintenance. Also, automatic slack adjusters will maintain brake balance, minimize travel and lessen air consumption. Manual slack adjusters must be constantly adjusted for minimal travel and reduced air consumption. |
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63. A slack adjuster essentially functions as a: A. gear B. lever C. anchor D. servo |
The correct answer is B. The slack adjuster is essentially a lever, which. multiplies force in proportion to its length. The brake adjuster’s length and the brake Chamber’s size are two variables commonly altered to meet braking requirements. |
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64. Technician A says coefficient of friction is the amount of heat absorbed into the drum. Technician B says brake shoes with high coefficient of friction will slow a truck with less application pressure. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is B. Coefficient of friction is defined as the resistance to movement between two surfaces in contact with each other. The amount of such resistance is known as the coefficient of friction (sometimes represented by the Greek letter ‘p,’ pronounced ‘mew’). Lining with a high coefficient of friction would slow a truck with less application pressure than a lining having a lower coefficient of friction. |
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65. According to some experts, air disc brakes are designed to: A. apply faster B. last longer C. decrease in-lane braking stability D. none of the above |
The correct answer is D. According to some experts, air disc brake technology improves in-lane braking stability as compared to S-Cam brakes. Small variations in lining friction or the drum surface on S-cam brakes can affect braking stability. Air disc brakes are designed to minimize this instability as pressure is applied constantly and efficiently to all wheels. |
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66. The right front wheel of a truck with hydraulic anti-lock brakes locks up when on a slippery surface. Technician A says the truck could have a defective wheel sensor. Technician B says the sensor checks for a lock-up condition and sends a signal to the hydraulic modulator. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technicians are right. Hydraulic anti-lock systems use a control module in conjunction with wheel speed sensors to establish the deceleration rate of the vehicle’s wheels during braking. If the control module determines that wheel lock-up is about to take place, it will issue commands to a hydraulic modulator. The modulator will then regulate fluid pressure to the wheels as instructed. |
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67. New generation ABS systems are designed to: A. allow the driver to apply with more foot pressure B. allow the pedal to be pumped C. default to non-ABS when a failure is detected D. none of the above |
The correct answer is C. All new-generation anti-lock systems are designed to default to what is typically called a ‘fail soft’ condition-that is, when there is an ABS malfunction, the brake system simply behaves as though there was no ABS. |
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68. A truck with air brakes takes an inordinate time to build up adequate air pressure. Oil has been found in the air brake system. Technician A says the compressor air filter could be clogged. Technician B says the compressor oil control rings could be worn. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B |
The correct answer is C, both Technicians are right. In addition to a slow air compressor build-up time, a plugged filter creates a vacuum in the compressor cylinder during the intake stroke. Oil is then sucked past the compressor’s piston rings. On the compression stroke, the piston pumps all of the accumulated oil through the discharge line, and right into the air system. A compressor can also pass oil into the system if its oil control rings are excessively worn. |
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69. Electronic Stability Control (ESC) is designed to: A. warn the driver if the brakes have failed |
The correct answer is D. ESC systems are integrated into the ABS and activate in situations where vehiclestability is crucial. Comparisons are made between the truck driver’s steering and brak- ing inputs and the truck’s response to those inputs. When ESC senses an abnormal condition such as an extreme lateral movement, it applies the brakes or reduces engine power. |
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70. When a truck is pulling to one side when braking, it could have: A. impractical imbalance B. mechanical imbalance C. braking instability D. adaptive coefficiency |
The correct answer is B. If the vehicle’s brakes are pulling to one side, grabbing too quickly, improperly releasing, or otherwise causing the vehicle to experience poor stopping ability, the system could be experiencing what is called ‘mechanical imbalance.’ |
