Commercial Vehicle Inspection, Air Brakes and Vehicle Systems
This domain tests the daily inspection and air-brake knowledge a Class C driver must demonstrate. The exam focuses on defect recognition, out-of-service decisions and the air-brake tests that prove the system will stop the bus.
Daily inspection
- Complete a pre-trip inspection before first use and a post-trip inspection; report defects in writing.
- Check brakes, tires, steering, lights, mirrors, horn, wipers, doors, emergency exits, fire extinguisher, first aid kit and wheelchair lift.
- A major defect that affects safe operation means the bus must not be driven until repaired. Keep inspection records as required.
Air brakes
- Build air pressure to governor cut-out (typically 120-125 psi), shut off the engine and watch for leakage.
- Perform the static leak test and applied leak test; check the low-pressure warning and spring-brake application.
- Drain air tanks to remove moisture; check slack adjusters and pushrods.
- Know that spring brakes apply automatically when air pressure drops too low; they are not a parking brake substitute on all grades.
Worked example
After building pressure, the driver shuts off the engine and listens. Pressure falls faster than the vehicle's allowed leak rate, and the low-pressure warning has not sounded at the normal point. The driver should treat this as a defect, not “wait and see.” The bus stays out of service until the leak is repaired and the warning and spring brakes are retested.
Traps
- Signing an inspection report without actually testing.
- Treating a minor air leak as normal.
- Assuming the warning buzzer is the only check; test spring-brake application.
- Not checking slack adjuster travel.