§393.70 covers coupling devices for tractor–semitrailer and truck–trailer combinations: fifth wheels, kingpins, pintle hooks, drawbars, safety chains, and the mounting hardware that ties them to the chassis. The rule requires that each be of adequate strength, properly secured, and equipped with a positive locking mechanism that cannot release unintentionally.
Severity weight + OOS
Severity weight 5 in the Vehicle Maintenance BASIC. Cracked or damaged fifth-wheel plates, mounting bolts that are missing or loose, kingpin damage, or a locking mechanism that cannot fully engage are OOS conditions under the NAS Out-of-Service Criteria. The failure mode is uncoupling under load — the most consequential equipment failure on a combination vehicle.
How it gets cited
The two patterns: (1) visible cracks at the fifth-wheel mounting brackets or in the plate itself, found by inspector visual; (2) a coupling test that reveals the jaws do not fully close around the kingpin — the trailer is "secured" but the locking pin is not seated.
How to prevent it
- Coupling inspection on every drop-and-hook — visual of the kingpin in the jaws, tug test against the brakes, look for the locking pin position.
- Annual fifth-wheel inspection should pull the plate, inspect mounting bolts, replace torn or thinning bushings, and re-grease.
- Treat any §393.70 finding as a drop-everything event — coupling failures are the highest-severity equipment incidents in the fleet.
How Roadworthy HQ helps
A coupling citation shows up in Roadworthy HQ as part of the inspection it came from, not as a record of its own: the app does not store individual violation codes. Log the roadside inspection on the vehicle's Inspections tab: date, state, level, driver, the number of violations, and whether it was out-of-service. For an out-of-service inspection the 15-day §396.9(d)(3) repair-certification countdown stays on that tab until you enter the certification date. The rule's 15 days cover every violation on the report, not only out-of-service ones, so for a non-OOS inspection that date is yours to track. The repair itself goes in the vehicle's maintenance log: date, type, what was done, who did it, and cost. DVIRs are logged per vehicle with the defect described in your own words, and a defect marked safety-affecting that is logged without a repair certification sends a critical alert.