Common DOT Brake Violations and How to Prevent Them
Brakes are the #1 vehicle out-of-service category. Learn the most common brake violations under 49 CFR Part 393, pushrod stroke limits, the 20% rule, and how to catch problems before roadside.
Every year, brake systems are the leading cause of vehicle out-of-service orders in CVSA inspection data and during CVSA's annual Operation Airbrake and Brake Safety Week. Most brake violations can be found and fixed in a few minutes in the yard.
Most-cited brake violations
- Brake out of adjustment (
§393.47(e),§393.48(a)): pushrod stroke at or beyond the adjustment limit for the chamber type. - Inoperative or defective brakes (
§393.48(a)): no braking action, broken components, or missing parts. - Air leaks (
§393.45): audible leaks at chambers, hoses, or fittings. - Chafed or damaged hoses and tubing (
§393.45): hoses rubbing through to the reinforcement ply. - Brake linings or pads (
§393.47): cracked, loose, missing, contaminated with oil or grease, or worn below minimum thickness. - Missing ABS lamp or ABS malfunction (
§393.55). - Low-air warning device (
§393.51) inoperative.
Pushrod stroke limits (common clamp-type chambers)
| Chamber type | Adjustment limit (standard stroke) | Adjustment limit (long stroke) |
|---|---|---|
| Type 20 | 1-3/4" | 2" |
| Type 24 | 1-3/4" | 2" (2-1/2" for 3" rated stroke) |
| Type 30 | 2" | 2-1/2" |
Measure applied stroke with 90–100 psi of reservoir pressure. Check the current CVSA OOSC tables for your exact chamber, because limits vary by type and rated stroke.
The 20% rule
A vehicle is placed out of service when the number of defective brakes equals or exceeds 20% of the service brakes on the vehicle or combination. A brake out of adjustment counts as one-half of a defective brake if it is less than 1/4" beyond the readjustment limit, and as a full defective brake if more. Some conditions are OOS by themselves, such as a missing or inoperative steer axle brake.
Prevention
- Check slack adjuster stroke during pre-trip, or use stroke indicators.
- Remember that automatic slack adjusters should not need manual adjustment. Frequent re-adjustment means a mechanical problem.
- Listen for leaks with the brakes applied.
- Look at linings and drums for cracks and oil contamination.
- Photograph anything questionable with DotCheck to get the likely CFR section and OOS severity.
FREQUENTLY ASKED QUESTIONS
What is the most common brake violation at roadside?
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Brakes out of adjustment is consistently one of the most frequently cited brake violations during roadside inspections.
What is the CVSA 20 percent brake rule?
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A vehicle is placed out of service when defective brakes equal or exceed 20 percent of the service brakes on the vehicle or combination, with partially out-of-adjustment brakes counting as one-half of a defective brake.
Should automatic slack adjusters be manually adjusted?
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Automatic slack adjusters should not routinely need manual adjustment. Repeated out-of-adjustment conditions indicate a mechanical problem that should be repaired.
This guide is for general information and pre-inspection preparation only. It is not legal advice. Always check the current text of 49 CFR at ecfr.gov and the current CVSA OOS Criteria.