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CDL Air Brakes Test

Air brake system parts: practice questions

Our CDL Air Brakes bank has 73 questions on this topic. Here are 5 of them with answers; the full mock exam draws from every topic, like the real one.

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Question 1

Air-braked trucks, buses, trailers and converter dollies built on or after what date must have ABS?

  1. March 1, 1998
  2. March 1, 1997
  3. January 1, 2000
  4. March 1, 1975
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A. March 1, 1998 — Other air brake vehicles (trucks, buses, trailers and converter dollies) built on or after March 1, 1998 must have ABS (CDL Manual 5.1.16)

Question 2

The safety relief valve releases air while you are driving. What does this mean?

  1. Something is wrong and a mechanic should fix it
  2. The tanks are full, so the system is simply venting the extra air
  3. The governor has switched to cut-in
  4. The spring brakes are about to apply
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A. Something is wrong and a mechanic should fix it — If the safety valve releases air, something is wrong. Have the fault fixed by a mechanic (CDL Manual 5.1.6)

Question 3

On a vehicle with a dual air brake system, what does the supply pressure gauge setup look like?

  1. One gauge per half of the system, or one gauge with two needles
  2. One gauge for each wheel, mounted next to each brake chamber
  3. A single needle that shows the lower of the two systems
  4. No gauge, only a warning light for each system
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A. One gauge per half of the system, or one gauge with two needles — With a dual system there is a gauge for each half of the system, or a single gauge with two needles (CDL Manual 5.1.9)

Question 4

On older vehicles, how might the parking brake control appear?

  1. A yellow diamond knob only
  2. A red eight-sided knob
  3. A foot pedal beside the clutch
  4. A round blue knob or a lever
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D. A round blue knob or a lever — On older vehicles it may be a round blue knob or some other shape, including a lever (CDL Manual 5.4.8)

Question 5

Where is the safety relief valve installed?

  1. In the line to each brake chamber, next to the slack adjuster
  2. In the last tank before the trailer connection
  3. In the first tank the compressor pumps air into
  4. On the dash next to the pressure gauge
Show the answer

C. In the first tank the compressor pumps air into — A safety relief valve is installed in the first tank the compressor pumps air to (CDL Manual 5.1.6)

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