Take CDL Air Brakes Practice Questions - CDL Air Brakes Knowledge Test Exam

QUESTION 1 / 25

What component compresses air for the air brake system?

Choose one answer below.

AThe air dryer✓BThe air compressor✓CThe brake chamber✓DThe slack adjuster✓

QUESTION 2 / 25

What is the typical air compressor governor cut-out pressure range?

Choose one answer below.

A60 to 80 psi✓B100 to 115 psi✓C125 to 135 psi✓D150 to 175 psi✓

QUESTION 3 / 25

At what pressure does the air compressor governor typically cut IN to resume pumping?

Choose one answer below.

A60 to 80 psi✓B100 to 115 psi✓C125 to 135 psi✓D145 to 150 psi✓

QUESTION 4 / 25

What is the purpose of the air dryer in the brake system?

Choose one answer below.

ATo cool the air before storage✓BTo remove moisture and oil before air reaches the tanks✓CTo increase compressed air pressure✓DTo warn the driver of low pressure✓

QUESTION 5 / 25

What is the function of the wet tank (supply or service reservoir)?

Choose one answer below.

AIt cools brake fluid✓BIt is the first storage tank where moisture collects before air moves to the other tanks✓CIt supplies air only to the trailer✓DIt activates the parking brakes✓

QUESTION 6 / 25

At what pressure does the safety valve in the supply tank typically open to release excess air?

Choose one answer below.

A100 psi✓B125 psi✓C150 psi✓D200 psi✓

QUESTION 7 / 25

What is the role of the foot valve (also called the treadle or service brake valve)?

Choose one answer below.

AIt locks the parking brake✓BIt supplies air to the brake chambers in proportion to how hard the driver presses the pedal✓CIt drains water from the tanks✓DIt controls the trailer air supply✓

QUESTION 8 / 25

What does the brake chamber do?

Choose one answer below.

AStores compressed air for emergencies✓BConverts air pressure into mechanical force through a pushrod✓CCools brake drums during use✓DActs as a backup for the parking brake✓

QUESTION 9 / 25

What is the role of the slack adjuster on an S-cam brake?

Choose one answer below.

AIt cushions the impact of hard braking✓BIt transfers force from the pushrod to the S-cam and can be adjusted to compensate for lining wear✓CIt bleeds water from the system✓DIt limits maximum air pressure✓

QUESTION 10 / 25

What does the S-cam do in an S-cam drum brake?

Choose one answer below.

AIt releases air from the lines✓BIt rotates between the brake shoes, forcing them outward against the drum✓CIt cools the brake drum✓DIt activates the low-pressure warning✓

QUESTION 11 / 25

How are spring (parking) brakes held in the released position?

Choose one answer below.

ABy engine vacuum✓BBy a hydraulic line✓CBy air pressure applied against the spring✓DBy a mechanical lock that the driver releases✓

QUESTION 12 / 25

What is the shape and color of the parking brake control knob in most modern CMVs?

Choose one answer below.

AA red 8-sided (octagonal) knob✓BA yellow diamond-shaped knob✓CA green round knob✓DA blue square knob✓

QUESTION 13 / 25

What is the shape and color of the trailer air supply control on a tractor?

Choose one answer below.

AA yellow diamond knob✓BA red 8-sided (octagonal) knob✓CA blue triangular knob✓DA green round knob✓

QUESTION 14 / 25

What is a dual air brake system?

Choose one answer below.

AA system that uses two compressors✓BA system with two completely separate air systems (primary and secondary), each controlling brakes on different axles✓CA system that uses both air and hydraulic fluid✓DA system with air-cooled drums✓

QUESTION 15 / 25

At what pressure must the low air pressure warning device activate at the latest?

Choose one answer below.

AAt 30 psi✓BAt 60 psi or higher✓CAt 90 psi✓DAt 120 psi✓

QUESTION 16 / 25

While driving, the low air pressure warning light comes on. What should you do?

Choose one answer below.

AContinue to your destination but watch the gauge✓BBring the vehicle to a safe stop as soon as possible and find the problem✓CApply the parking brake while still moving✓DPump the brake pedal to build pressure✓

QUESTION 17 / 25

How often should air tank drain valves be operated to remove water and oil?

Choose one answer below.

AOnce a year✓BAfter every long trip only✓CDaily✓DOnly when the warning light comes on✓

QUESTION 18 / 25

What is the maximum allowable air loss rate for a single vehicle with the brakes released (static leak rate)?

Choose one answer below.

A1 psi per minute✓B2 psi per minute✓C3 psi per minute✓D4 psi per minute✓

QUESTION 19 / 25

What is the maximum allowable air loss rate for a combination vehicle with the brakes released?

Choose one answer below.

A1 psi per minute✓B2 psi per minute✓C3 psi per minute✓D5 psi per minute✓

QUESTION 20 / 25

What is the maximum allowable air loss rate for a single vehicle with the brakes APPLIED (applied leak rate)?

Choose one answer below.

A2 psi per minute✓B3 psi per minute✓C4 psi per minute✓D5 psi per minute✓

QUESTION 21 / 25

What is the maximum allowable air loss rate for a combination vehicle with the brakes APPLIED?

Choose one answer below.

A2 psi per minute✓B3 psi per minute✓C4 psi per minute✓D6 psi per minute✓

QUESTION 22 / 25

During the air brake pre-trip inspection, how do you test the low air pressure warning device?

Choose one answer below.

AStart the engine and watch the gauge✓BBuild air pressure to governor cut-out, shut off the engine, turn the key to the on position, and fan the brakes until the warning activates✓CApply the parking brake and listen for the alarm✓DDrain the wet tank only✓

QUESTION 23 / 25

During the air brake pre-trip, how do you test that the spring brakes apply automatically?

Choose one answer below.

AApply the foot brake hard while driving✓BContinue fanning the brakes until air pressure drops far enough; the spring brakes should apply between roughly 20 and 45 psi✓CPull the parking brake at 60 psi✓DDrain the secondary tank only✓

QUESTION 24 / 25

In normal stops with air brakes, you should:

Choose one answer below.

AStab the pedal hard, then release✓BApply the brakes firmly and steadily until you slow enough to safely shift to neutral or a lower gear✓CApply the parking brake✓DPump the pedal rapidly✓

QUESTION 25 / 25

What is controlled braking in an emergency stop with air brakes?

Choose one answer below.

APressing the pedal as hard as possible and holding it✓BApplying the brakes as hard as you can without locking the wheels, then releasing slightly if wheels lock✓CUsing only the parking brake✓DPumping the pedal rapidly✓