DOT Vehicle Maintenance & Repair Standards 3 — Questions and Answers
Question 1: When inspecting an automatic slack adjuster, at what pushrod stroke is the brake considered out of adjustment for a type-30 chamber?
- Over 1.5 inches
- Over 2 inches (Correct answer)
- Over 2.5 inches
- Over 3 inches
Correct answer: Over 2 inches
For a Type 30 brake chamber, the out-of-service threshold is a pushrod stroke exceeding 2 inches at 90 psi according to CVSA criteria.
Question 2: A vehicle's air compressor governor cuts in at 100 psi and cuts out at 125 psi. Is this within acceptable range?
- Yes, both values are within normal operating range (Correct answer)
- No, cut-out pressure is too high
- No, cut-in pressure is too low
- No, the pressure differential is too narrow
Correct answer: Yes, both values are within normal operating range
Normal cut-in pressure is 85–100 psi and cut-out is 120–135 psi, so 100/125 psi is within the acceptable operating range.
Question 3: Which of the following exhaust system defects is an automatic out-of-service condition?
- Loose heat shield on a muffler
- Exhaust leak forward of or directly below the cab (Correct answer)
- Slightly discolored exhaust pipe
- Exhaust system louder than 80 dB
Correct answer: Exhaust leak forward of or directly below the cab
An exhaust leak located forward of or directly below the cab is an out-of-service condition because carbon monoxide can enter the occupant compartment.
Question 4: A CMV's fuel tank has a pinhole leak that drips fuel when the vehicle is stationary. This defect is classified as:
- A minor defect requiring repair within 7 days
- An out-of-service condition (Correct answer)
- Acceptable if fuel loss is under 1 oz per minute
- A driver-reportable item only
Correct answer: An out-of-service condition
Any fuel system leak is an out-of-service condition under 49 CFR 393.67 because of the fire and explosion hazard it creates.
Question 5: What does the 'Low Air Warning' device on an air brake system activate?
- When reservoir pressure drops below 60 psi (Correct answer)
- When service brake application pressure drops below 45 psi
- When air dryer cartridge is saturated
- When system pressure exceeds 135 psi
Correct answer: When reservoir pressure drops below 60 psi
The low air warning device must activate before reservoir pressure drops below 60 psi, giving the driver time to safely stop the vehicle.
Question 6: During a Level I inspection, an inspector checks the kingpin-to-apron engagement on a fifth wheel. Minimum engagement requires:
- The kingpin must be fully visible above the apron
- The locking jaws must be fully closed around the kingpin (Correct answer)
- At least 50% of the kingpin height must be above the apron plate
- The safety latch must be in the open position
Correct answer: The locking jaws must be fully closed around the kingpin
The fifth wheel locking jaws must be fully closed and locked around the kingpin with the safety latch engaged to prevent trailer separation.
Question 7: Under 49 CFR 393.75, a tire is considered defective and out-of-service if it has:
- A repaired puncture on a non-load-bearing area
- Fabric exposed through the tread (Correct answer)
- Minor sidewall scuffing from curb contact
- Tread wear indicators at 3/32 inch on a steer tire
Correct answer: Fabric exposed through the tread
Any tire with fabric (ply) exposed through the tread or sidewall is an out-of-service condition because structural integrity is compromised.
DOT Vehicle Maintenance & Repair Standards 3
When inspecting an automatic slack adjuster, at what pushrod stroke is the brake considered out of adjustment for a type-30 chamber?