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Red Seal Heavy Duty Equipment Technician study materials
Red Seal Heavy Duty Equipment Technician study resources

Red Seal Heavy Duty Equipment Technician: Brake, Steering, and Suspension Systems

Red Seal Heavy Duty Equipment Technician · Work through your exam, one topic at a time.

All guide sections

Brake, Steering, and Suspension Systems

What this domain tests

Air brake adjustment and component identification, hydraulic and air-over-hydraulic brakes, ABS basics, hydrostatic and mechanical steering geometry, and suspension inspection on heavy trucks and off-road machines.

Core rules

  • Air system: compressor feeds an air dryer, then reservoirs with drain valves. Governor cut-out is typically around 830–900 kPa (120–130 psi) and cut-in about 100 psi lower. Low pressure warning and spring-brake application must occur before pressure falls to about 310 kPa (45 psi).
  • Slack adjusters and pushrod stroke: measure stroke at the chamber with the brakes applied and system at full pressure. Compare to the limit stamped on the chamber. A stroke over the limit means adjustment; if it will not hold adjustment, the slack adjuster or chamber is worn.
  • Spring brakes (maxi): air releases the spring; loss of air applies the brake. Caging compresses the spring mechanically for towing only - never rely on caging for service.
  • Steering: hydrostatic systems use an orbitrol unit; a worn pump gives hard steering when hot, while a failed relief or internal leak gives uneven effort. Mechanical linkage needs toe, caster, camber, and Ackermann geometry checks; a bent tie rod shows as off-centre steering wheel and uneven tire wear.
  • Suspension: leaf springs, air bags with ride-height valves, and shock absorbers. Ride height is set at the valve with the machine at normal load, not empty.

Worked example

A truck pulls to one side while braking. Check pushrod stroke on all chambers first - a long stroke on one side means that brake applies late. If strokes are within limit, inspect for oil-contaminated linings, seized S-cam bushings, or a kinked hose. The stroke measurement is the cheapest test and eliminates adjustment before you pull drums.

Traps

  • Adjusting a slack adjuster that is already at the end of its travel instead of replacing it.
  • Setting ride height with the machine empty or on uneven ground.
  • Ignoring that a caged spring brake has no parking function.