Chassis, Steering, Suspension, and Brakes
This is the largest and most safety-critical inspection domain. Chassis: inspect frame rails for cracks and loose fasteners, crossmembers, and the fifth wheel (mounting, jaw/lock condition, lubrication). Steering: check tie-rod ends, drag link, kingpins, and steering gear for play and leaks; verify power steering fluid level and hose condition. Suspension: inspect springs (broken leaves, cracked hangers, missing U-bolts), air springs for cracks and chafing, shocks for leaks, and torque rods/bushings for wear. Confirm air suspension ride-height and leveling valve function.
Brakes: understand foundation brake components (drums, rotors, pads/linings, slack adjusters, chambers) and air system checks (governor cut-in/cut-out, leak-down, low-pressure warning). Know that automatic slack adjusters should be checked for correct installed length and not manually adjusted to mask a problem. Recognize pushrod stroke limits and that a brake out of adjustment is an out-of-service condition.
Traps: assuming a slack adjuster that "looks fine" is adjusted correctly (measure stroke), missing a cracked spring hanger, confusing an air leak at a chamber with a bad valve, and overlooking a loose fifth-wheel jaw. Another trap is judging brake lining by thickness alone while ignoring cracks or oil contamination.
Rule of thumb: if it steers, stops, or holds the load, a defect is out-of-service until proven otherwise. Worked example: a tractor pulls right when braking. Inspect for a seized slack adjuster or contaminated lining on one side, measure pushrod stroke against the limit, and repair before return to service.