CDT Vehicle Operations & Maintenance 3 — Questions and Answers
Question 1: What does the 'pushrod travel' measurement indicate during an air brake inspection?
- How far the brake pedal depresses before air flows
- The distance a brake chamber pushrod moves when brakes are applied (Correct answer)
- The length of the brake drum lining
- The slack adjuster rotation angle
Correct answer: The distance a brake chamber pushrod moves when brakes are applied
Pushrod travel (stroke) measures how far the pushrod extends when brakes are applied; excessive travel indicates out-of-adjustment brakes.
Question 2: When coupling a semi-trailer to a tractor, the LAST step before moving should be:
- Check that the fifth wheel is lubricated
- Tug test — pull forward against locked trailer brakes to confirm coupling (Correct answer)
- Connect the electrical cord
- Raise the landing gear fully
Correct answer: Tug test — pull forward against locked trailer brakes to confirm coupling
The tug test confirms the kingpin is properly locked in the fifth wheel jaws before the driver moves the combination vehicle.
Question 3: What is the purpose of automatic slack adjusters on commercial vehicles?
- To automatically apply the parking brake when parked
- To maintain proper brake adjustment as linings wear (Correct answer)
- To regulate air compressor output pressure
- To synchronize front and rear brake application
Correct answer: To maintain proper brake adjustment as linings wear
Automatic slack adjusters continuously maintain the correct distance between the brake lining and drum as linings wear, reducing manual adjustment needs.
Question 4: A driver smells something burning after a long downhill grade. The MOST likely cause is:
- Engine oil burning off the exhaust manifold
- Overheated service brakes from excessive use (Correct answer)
- Transmission fluid leak
- Fuel injector fouling
Correct answer: Overheated service brakes from excessive use
A burning smell after a downgrade almost always indicates overheated brake drums and linings from excessive brake use instead of proper engine braking.
Question 5: Under FMCSA regulations, which defect found during a pre-trip inspection requires the vehicle to be placed Out of Service immediately?
- A burned-out license plate light
- A cracked brake drum (Correct answer)
- A missing mud flap
- A slightly low tire that still holds pressure
Correct answer: A cracked brake drum
A cracked brake drum is an Out of Service condition per FMCSA regulations because it compromises braking effectiveness and safety.
Question 6: What is the recommended procedure when a tire blows out on the front axle of a truck?
- Brake hard immediately to stop as quickly as possible
- Hold the steering wheel firmly, avoid braking hard, and steer to safety (Correct answer)
- Turn the wheel sharply to the shoulder
- Engage the parking brake to stabilize the vehicle
Correct answer: Hold the steering wheel firmly, avoid braking hard, and steer to safety
Front blowouts can cause sudden loss of steering control; the driver must grip the wheel firmly, avoid hard braking, and allow the vehicle to decelerate while steering to a safe stop.
Question 7: What does the term 'gross vehicle weight rating' (GVWR) represent?
- The weight of the vehicle when empty
- The maximum loaded weight the vehicle is designed to safely operate at (Correct answer)
- The combined weight of cargo only
- The maximum weight the engine can propel at highway speed
Correct answer: The maximum loaded weight the vehicle is designed to safely operate at
GVWR is the manufacturer-specified maximum safe operating weight of a single vehicle including its payload, fluids, and occupants.
CDT Vehicle Operations & Maintenance 3
What does the 'pushrod travel' measurement indicate during an air brake inspection?