§393.53(b) requires every air-braked CMV manufactured on or after October 20, 1994 to be equipped with automatic slack adjusters on every brake. The point of the regulation: a properly-functioning automatic slack adjuster keeps the brake within the §393.47(e) readjustment limit without manual intervention. A seized or non-functioning automatic slack adjuster causes the brake to go out of adjustment, which triggers the §393.47 finding.
The pairing problem
Roadside inspectors who find a brake out of adjustment under §393.47 frequently cite §393.53 alongside if the slack adjuster is automatic and is not doing its job. Two findings, two severity weights, one root cause. The 20% rule (§393.47(f)) places the vehicle OOS — and §393.53 is often the underlying defect.
Manual adjustment is not the answer
If an automatic slack adjuster is out of adjustment, the corrective action is to replace the slack adjuster — not to manually adjust it. Manually adjusting a defective automatic slack adjuster is a §393.53 violation in itself; FMCSA guidance and CVSA training materials are explicit.
How to prevent it
- Annual inspection §396.17 includes a slack-adjuster stroke check at every wheel position.
- Track installed-date and replacement-mileage per slack adjuster — they wear like other brake components.
- After every §393.47 brake-adjustment citation, inspect the slack adjuster and replace if it's not maintaining adjustment.
How Roadworthy HQ helps
A slack-adjuster 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. The §396.17 annual inspection report uploads to the vehicle, with reminders 60, 30, and 7 days before the next one is due.