CDL Combination Vehicles TestCoupling and UncouplingHard
A driver is inspecting the kingpin. What is the maximum allowable amount of wear on the kingpin's diameter before it must be replaced or repaired, according to federal regulations?
- A1/16 inch (1.5875 mm)
- B1/8 inch (3.175 mm)
- C3/8 inch (9.525 mm)
- D1/4 inch (6.35 mm)
Show answer & explanationAnswer & explanation
Correct answer: B. 1/8 inch (3.175 mm)
Federal regulations (specifically FMCSA guidance related to 49 CFR Part 393) state that a kingpin should not be worn more than 1/8 inch from its original diameter. Exceeding this limit compromises the integrity of the coupling.
Why the other options are wrong
- A. While 1/16 inch wear is significant, the maximum allowable is double that.
- C. This is far beyond safe operating limits for kingpin wear.
- D. This is excessive wear and would be unsafe.
Kingpin Wear Limit
The maximum allowable reduction in the kingpin's diameter due to wear before it must be replaced or repaired to ensure safe coupling.
- Max wear: 1/8 inch from original diameter.
- Critical for coupling integrity.
- Checked during pre-trip inspections.
- Exceeding limit is a safety violation.
Memory trick: One-Eighth Inch, No More, or it's out the door!