HEAVY TRUCK BRAKES EXAMS SCRIPT QUESTIONS AND
ANSWERS 2025/2026
✔✔When a properly functioning treadle valve is actuated by foot pressure, which of the
following will determine what pressure is metered out to actuate the primary and
secondary service circuits?
A. Mechanical force is applied to the treadle
B. Actual travel of the primary piston
C. Actual system pressure at the time of the application
D. Mechanical force applied to the relay piston - ✔✔Mechanical force applied to the
treadle
✔✔Technician A says that the relay section of a dual circuit foot valve is actuated
mechanically under normal operation. Technician B says that a primary piston of a foot
valve is actuated mechanically under normal operation. Who is correct? - ✔✔Tech B
✔✔Technician A says that a trailer service brake signal is always sourced from the
tractor primary circuit. Technician B says that a trailer service signal can only pass
through a tractor protection valve when it is in its ON state. Who is correct? - ✔✔Tech B
✔✔Technician A says that most current highway tractors use a 3-line TP valve.
Technician B says that a 2-line TP valve will remain OFF until the trailer air supply dash
button is depressed. Who is correct? - ✔✔Tech B
✔✔How man anchor pins are used for a pair of S-cam actuated brake shoes? - ✔✔Two
✔✔What term is used to measure the aggressiveness of friction linings? - ✔✔The
coefficient of friction
✔✔In current practices in a truck service facilities, when should a truck brake drum be
machined? - ✔✔Only when new
✔✔What is the maximum permitted service oversize dimension permitted for a standard
16.5 brake drum be machined? - ✔✔0.120-inch
✔✔When under severe braking the wheels of a trailer lock causing it to spin around
while the tractor remains in a straight ahead position, the condition is known as? -
✔✔Trailer swing
✔✔What is the function of the compressor on a truck air brake system? - ✔✔Compress
ambient air
ANSWERS 2025/2026
✔✔When a properly functioning treadle valve is actuated by foot pressure, which of the
following will determine what pressure is metered out to actuate the primary and
secondary service circuits?
A. Mechanical force is applied to the treadle
B. Actual travel of the primary piston
C. Actual system pressure at the time of the application
D. Mechanical force applied to the relay piston - ✔✔Mechanical force applied to the
treadle
✔✔Technician A says that the relay section of a dual circuit foot valve is actuated
mechanically under normal operation. Technician B says that a primary piston of a foot
valve is actuated mechanically under normal operation. Who is correct? - ✔✔Tech B
✔✔Technician A says that a trailer service brake signal is always sourced from the
tractor primary circuit. Technician B says that a trailer service signal can only pass
through a tractor protection valve when it is in its ON state. Who is correct? - ✔✔Tech B
✔✔Technician A says that most current highway tractors use a 3-line TP valve.
Technician B says that a 2-line TP valve will remain OFF until the trailer air supply dash
button is depressed. Who is correct? - ✔✔Tech B
✔✔How man anchor pins are used for a pair of S-cam actuated brake shoes? - ✔✔Two
✔✔What term is used to measure the aggressiveness of friction linings? - ✔✔The
coefficient of friction
✔✔In current practices in a truck service facilities, when should a truck brake drum be
machined? - ✔✔Only when new
✔✔What is the maximum permitted service oversize dimension permitted for a standard
16.5 brake drum be machined? - ✔✔0.120-inch
✔✔When under severe braking the wheels of a trailer lock causing it to spin around
while the tractor remains in a straight ahead position, the condition is known as? -
✔✔Trailer swing
✔✔What is the function of the compressor on a truck air brake system? - ✔✔Compress
ambient air
