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Question

Difficulty: MediumEn-Route and Post-Trip Inspections

Upon returning to a freight distribution terminal, a driver carries out a post-trip walk-around inspection to complete the daily vehicle condition documentation. Which of the following observed conditions constitutes a safety-critical defect that must be reported on the Driver Vehicle Inspection Report (DVIR)?

  1. A
    A steering wheel with an outer diameter of 20 inches that exhibits 1.5 inches of rotational free play before the front wheels respond
  2. B
    A manual slack adjuster on a drive axle that allows 0.75 inches of pushrod movement when pulled firmly by hand with the parking brakes released
  3. A front steering axle tire displaying a remaining tread depth of 3/32 inch in a major tread grooveAnswer
  4. D
    An emergency equipment storage compartment stocked with three red reflective warning triangles, a set of spare electrical fuses, and a fully charged 10 B:C fire extinguisher

Answer

A front steering axle tire displaying a remaining tread depth of 3/32 inch in a major tread groove
Federal commercial vehicle safety regulations dictate that front steer axle tires must maintain at least 4/32 inch of tread depth in every major groove. A measurement of 3/32 inch represents an out-of-tolerance condition that compromises steering grip and water evacuation, requiring formal notation on the daily Driver Vehicle Inspection Report (DVIR) so repairs or tire replacement can occur prior to the next dispatch.

Step-by-Step Solution

1
Evaluate the mechanical tolerance of the steering system
Free play of 1.5 inches on a 20-inch wheel is under the 2.0-inch (10-degree) maximum allowable threshold, making it acceptable.
Federal CDL standards permit up to approximately 2 inches of steering wheel play on a standard 20-inch wheel.
2
Evaluate the brake pushrod stroke measurement
A 0.75-inch manual pushrod movement when pulled by hand with brakes released is within the safe operational limit (less than 1 inch).
Pushrod travel within 1 inch by hand demonstrates that the manual slack adjuster does not require readjustment.
3
Evaluate the emergency safety equipment
The vehicle contains the required three reflective triangles, spare fuses, and a properly rated fire extinguisher.
FMCSR requires these specific three items in working order, so no defect exists here.
4
Evaluate steer axle tire tread depth requirements
A tread depth of 3/32 inch on a steer axle tire violates the mandatory 4/32-inch minimum requirement.
While non-steer tires require only 2/32 inch, steer tires strictly mandate 4/32 inch in every major groove to ensure directional control and prevent hydroplaning.

Key Concept

Post-trip vehicle inspection defect identification and minimum component safety tolerances
Estimated Time:1m 0s
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Topics

En-Route and Post-Trip Inspections

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