Inspecting Air Brake Systems
The walk-around mindset
An air brake inspection is systematic: check for damage and leaks first, then test function. Do it the same way every time so nothing is skipped.
What to look for
- Hoses and lines - cracks, chafing, bulges, and rubbing against sharp edges or moving parts.
- Tanks - secure mounting, no heavy rust or dents, drain valves present and operable.
- Brake chambers - cracked or dented housings, loose clamps, and a pushrod that is not bent.
- Slack adjusters - not broken, not welded, and the pushrod angle within the normal operating range (about 90 degrees to the slack adjuster when the brakes are applied).
- Drums, linings, and shoes - visible cracks, oil or grease contamination, and adequate lining thickness.
- Compressor belt - present, tight, and not frayed.
The leak and function checks
With the engine running and the system fully charged, shut the engine off and listen. A steady hiss is a leak. Then apply and hold the brake pedal and listen again for leaks; also check that the pedal does not creep toward the floor. Release and confirm the brakes release fully without dragging.
The applied-stroke check
Pull the pushrod out by hand (or have an assistant apply the brakes) and measure travel. Excessive pushrod travel means the brakes are out of adjustment or a chamber is faulty.
Traps
Questions often describe a slack adjuster that is welded or a pushrod at a poor angle and ask whether the vehicle can be driven. The answer is no - those are out-of-service conditions. Another trap is confusing an air leak (hiss) with a mechanical problem; always identify the source before deciding.
Rule of thumb
"Look, listen, feel, then test." Damage and leaks before function tests, and never sign off on a vehicle with an identified defect.