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Chapter 31
End of Chapter Review Questions Answer Key
1. Which of the following is the best practice when instructed to block the wheels on a
tractor/trailer combination?
2. What is the required amount of slack adjuster free travel on a properly adjusted,
manual S-cam brake?
3. Which of the following foundation brake components are lubricated with chassis
grease, either for component life or as part of a lube job?
4. A 161/2 inch (420 mm) brake drum specified to have a machine limit of 0.090 inch
(2.3 mm) over and a maximum dimension of 0.120 inch (3 mm) over is measured at
0.098 inch (2.5 mm) over at a brake overhaul. Technician A says that the drum can be
turned on a drum lathe, providing that the maximum dimension of 0.120 inch (3.0
mm) is observed. Technician B says that the drum can be legally returned to service
without being turned. Who is correct?
5. A tandem axle trailer equipped with S-cam brakes has all four slack adjusters
originally set with a 6-inch (150 mm) dimension from the clevis pin to the camshaft.
One slack adjuster is replaced, and because of a different hole arrangement in the new
slack adjuster, it is set at 61/2 inches (165 mm). Which of the following is more likely
to result?
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6. When adjusting a manual slack adjuster on an S-cam foundation brake, Technician A
says that the lock collar should be retracted and the adjusting nut always rotated
clockwise to decrease free travel. Technician B says that free travel can be reduced
only when the adjusting nut is rotated counterclockwise. Who is correct?
7. A set of brake linings has become glazed because of oil saturation by a failed wheel
seal. Technician A says that pressure washing the foundation brake components
should be sufficient to remove the effects of the oil saturation. Technician B says that
the best practice is to replace the brake linings on both wheels on the affected axle.
Who is correct?
8. When adjusting S-cam brakes on a trailer equipped with manual slack adjusters,
which of the following must be true?
9. An original equipment 45-degree elbow on a line exiting a relay valve supplying a
service chamber is replaced by a 90-degree elbow. Technician A says that this should
have no effect on brake performance because it is the service application pressure that
determines braking force. Technician B says that the use of the 90-degree elbow
increases flow restriction and can affect pneumatic timing. Who is correct?
10. Technician A says that it is recommended practice to disassemble and replace the
service diaphragm in a spring brake assembly to minimize the cost of replacing the
complete spring chamber. Technician B says that it is no longer possible to change the
hold-off diaphragms in most spring brake assemblies because the band clamp cannot
be unbolted. Who is correct?
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11. What is the main function of a hold-off diaphragm?
12. When an S-cam foundation brake slack adjuster is in the fully applied position, ideally
the slack adjuster-to-pushrod angle should be:
13. A tri-axle trailer is equipped with five S-cam slack adjusters correctly set at an
effective length of 6 inches (150 mm) and one incorrectly installed at 51/2 inches (140
mm). How much less brake torque will be applied at the brake with the incorrectly set
slack adjuster when the service application pressure is 100 psi (7 bar) on a 30-square-
inch (194 square cm) chamber?
14. A leaking axle seal has saturated the brake shoe linings and caused them to glaze.
Technician A says that the shoes should be immersed in solvent before being returned
to service. Technician B says that if the brake shoes on both sides of the axle are not
replaced, brake torque balance could be affected. Who is correct?
15. Technician A says that it is good practice to machine a new drum before putting it
into service because it trues the drum to the wheel. Technician B says that most heat
discoloration and checking is easy to remove on used drums when brakes are serviced
by skimming the drum on a lathe. Who is correct?
16. When a safety pop-off valve continuously unloads, which of the following should be
performed first?
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17. What is the usual freestroke travel window of a properly adjusted, automatic S-cam
brake slack adjuster?
18. What is the usual specified maximum S-cam endplay permitted when installing a
slack adjuster?
19. What is the adjustment stroke limit for a 24-Series brake chamber?
20. What is the adjustment stroke limit for a standard 30-Series brake chamber?