CDL CLASS A AIR BRAKES TEST PRACTICE
QUESTIONS AND ANSWERS/ TOPICS COVERED:
AIR BRAKE SYSTEM COMPONENTS, DUAL AIR
SYSTEMS, INSPECTING AIR BRAKES, EMERGENCY
PROCEDURES, BRAKE ADJUSTMENT, LOW
PRESSURE WARNINGS
Part 1: Air Brake System Components (Questions 1-15)
Question 1
What component pumps compressed air into the storage tanks?
A) Air governor
B) Air compressor
C) Air dryer
D) Brake pedal
Correct Answer: B) Air compressor
Rationale: The air compressor is the heart of the air brake system. It
is driven by the engine and pumps air into the storage tanks, building
the air pressure needed to operate the brakes .
Question 2
What controls when the air compressor pumps air into the tanks and
when it stops?
,A) Safety valve
B) Brake pedal
C) Air governor
D) Supply pressure gauge
Correct Answer: C) Air governor
Rationale: The governor sets the minimum and maximum air pressure
levels. It typically cuts in at about 100 psi and cuts out at about 125
psi .
Question 3
The supply pressure gauge tells you:
A) How much air pressure is being applied to the brakes
B) The amount of air pressure in the tanks
C) The temperature of the brake drums
D) The vehicle's speed
Correct Answer: B) The amount of air pressure in the tanks
Rationale: The supply pressure gauge indicates how much compressed
air is stored in the tanks. This is critical information because low
pressure means the brakes may not function properly .
Question 4
The application pressure gauge shows:
A) Total air pressure in all tanks
B) How much air pressure you are applying to the brakes
C) The pressure in the emergency system only
D) The vehicle's weight on the brakes
,Correct Answer: B) How much air pressure you are applying to the
brakes
Rationale: While the supply gauge shows available pressure, the
application gauge shows how much you're actually sending to the brakes
when you press the pedal. This helps you gauge braking force .
Question 5
What is the most common type of foundation brake found on heavy
vehicles?
A) Disc brakes
B) Wedge drum brakes
C) S-cam drum brakes
D) Electric brakes
Correct Answer: C) S-cam drum brakes
Rationale: S-cam drum brakes are the standard foundation brake on
most heavy trucks and buses. When air pressure pushes the push rod,
it turns the S-cam, which forces the brake shoes against the drum .
Question 6
When you apply the brakes, the brake shoes and linings are pushed
against:
A) The slack adjuster
B) The S-cam
C) The inside of the brake drum
D) The brake chamber
Correct Answer: C) The inside of the brake drum
, Rationale: Friction is created when the brake shoes press outward
against the inside surface of the brake drum, slowing the wheel's
rotation .
Question 7
What holds the air in the tanks if there is a leak in the air
compressor?
A) The safety valve
B) One-way check valves
C) The governor
D) The drain valves
Correct Answer: B) One-way check valves
Rationale: Check valves are installed between the compressor and the
first tank. They allow air to flow only in one direction. If the
compressor develops a leak, these valves prevent air from escaping
back through the compressor .
Question 8
At what pressure (PSI) does the air compressor typically stop pumping
air (governor cut-out)?
A) 100 psi
B) 125 psi
C) 150 psi
D) 85 psi
Correct Answer: B) 125 psi
QUESTIONS AND ANSWERS/ TOPICS COVERED:
AIR BRAKE SYSTEM COMPONENTS, DUAL AIR
SYSTEMS, INSPECTING AIR BRAKES, EMERGENCY
PROCEDURES, BRAKE ADJUSTMENT, LOW
PRESSURE WARNINGS
Part 1: Air Brake System Components (Questions 1-15)
Question 1
What component pumps compressed air into the storage tanks?
A) Air governor
B) Air compressor
C) Air dryer
D) Brake pedal
Correct Answer: B) Air compressor
Rationale: The air compressor is the heart of the air brake system. It
is driven by the engine and pumps air into the storage tanks, building
the air pressure needed to operate the brakes .
Question 2
What controls when the air compressor pumps air into the tanks and
when it stops?
,A) Safety valve
B) Brake pedal
C) Air governor
D) Supply pressure gauge
Correct Answer: C) Air governor
Rationale: The governor sets the minimum and maximum air pressure
levels. It typically cuts in at about 100 psi and cuts out at about 125
psi .
Question 3
The supply pressure gauge tells you:
A) How much air pressure is being applied to the brakes
B) The amount of air pressure in the tanks
C) The temperature of the brake drums
D) The vehicle's speed
Correct Answer: B) The amount of air pressure in the tanks
Rationale: The supply pressure gauge indicates how much compressed
air is stored in the tanks. This is critical information because low
pressure means the brakes may not function properly .
Question 4
The application pressure gauge shows:
A) Total air pressure in all tanks
B) How much air pressure you are applying to the brakes
C) The pressure in the emergency system only
D) The vehicle's weight on the brakes
,Correct Answer: B) How much air pressure you are applying to the
brakes
Rationale: While the supply gauge shows available pressure, the
application gauge shows how much you're actually sending to the brakes
when you press the pedal. This helps you gauge braking force .
Question 5
What is the most common type of foundation brake found on heavy
vehicles?
A) Disc brakes
B) Wedge drum brakes
C) S-cam drum brakes
D) Electric brakes
Correct Answer: C) S-cam drum brakes
Rationale: S-cam drum brakes are the standard foundation brake on
most heavy trucks and buses. When air pressure pushes the push rod,
it turns the S-cam, which forces the brake shoes against the drum .
Question 6
When you apply the brakes, the brake shoes and linings are pushed
against:
A) The slack adjuster
B) The S-cam
C) The inside of the brake drum
D) The brake chamber
Correct Answer: C) The inside of the brake drum
, Rationale: Friction is created when the brake shoes press outward
against the inside surface of the brake drum, slowing the wheel's
rotation .
Question 7
What holds the air in the tanks if there is a leak in the air
compressor?
A) The safety valve
B) One-way check valves
C) The governor
D) The drain valves
Correct Answer: B) One-way check valves
Rationale: Check valves are installed between the compressor and the
first tank. They allow air to flow only in one direction. If the
compressor develops a leak, these valves prevent air from escaping
back through the compressor .
Question 8
At what pressure (PSI) does the air compressor typically stop pumping
air (governor cut-out)?
A) 100 psi
B) 125 psi
C) 150 psi
D) 85 psi
Correct Answer: B) 125 psi
