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Iowa CDL — Air Brakes Practice Test 1

The Iowa CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.

This practice test follows that format: 25 questions, pass with 20 correct. Answer every page, then grade it to see the answers and explanations.

Questions 1–10 of 25

  1. 1.On Iowa's inspection test, you check the brake lines and hoses at the steering axle. According to the manual, what may a loss of air pressure in those lines cause?
  2. 2.On your walk-around you find cracks in several brake drums, and each drum has a friction area 6 inches wide. Which crack is longer than the manual allows?
  3. 3.Braking hard on ice in a truck without ABS, you lock up the front steering wheels. What is the immediate result?
  4. 4.Your truck's air compressor is driven by gears off the engine rather than by a belt. How does that change the air brake check in the engine compartment step?
  5. 5.In Iowa's air brake check, you have just finished the leakage test. What should you do about the engine before starting the low air warning test?
  6. 6.During the engine-area fluid check on Iowa's inspection test, which fluid on the list applies only to vehicles with hydraulic brakes, not air brakes?
  7. 7.You drive a tractor-trailer with ABS on both the tractor and the trailer. How much braking force does the manual tell you to use when you slow down?
  8. 8.Which statement about the air compressor does NOT match the manual?
  9. 9.You fail the air brake check during Iowa's vehicle inspection test. Can you move on to the basic vehicle control test?
  10. 10.In a truck with a dual air brake system, the low air light and buzzer come on. One gauge still reads 110 psi while the other is falling. What should you do?

0 of 25 answered