§393.42(a) requires every CMV to be equipped with brakes acting on all wheels. Limited exceptions exist for certain trailers under 3,000 lb GVWR towed at the rear of another CMV, certain loaded house-moving dollies, and pre-1980 specific equipment. For everything operating commercially today, every wheel position has a brake.
OOS connection
§393.42 is the foundational requirement; §393.47 is the in-service standard the brakes must meet. The 20% rule (when 20% or more of the service brakes on the vehicle are defective, the vehicle is OOS) is in the NAS Out-of-Service Criteria and is the most-cited brake OOS condition.
Severity weight
Severity weight 4 in the Vehicle Maintenance BASIC. Brake findings have a multiplicative effect — §393.42, §393.47, §393.53 (slack adjusters), and §392.7 frequently appear together on the inspection report.
How to prevent it
- Annual inspection per §396.17 includes a brake-stroke check at every wheel position.
- Spread-trailer combinations (lift axles, certain doubles) — verify every dropped-axle position has its brake operating; lift-axle controls left in the up position can mask a non-functional brake.
- PM schedule includes brake-shoe replacement at the mileage interval recommended by the chassis manufacturer.
How Roadworthy HQ helps
The vehicle's §396.3 PM schedule and §396.17 annual-inspection record live alongside every DVIR. Findings here roll up into the audit binder so brake-related compliance is one click to demonstrate.