Suspension and Steering
Fundamentals
Understand leaf springs, air suspension with height-control valves, shock absorbers (they control motion, not load), kingpins and ball joints, tie rods, drag links, steering gears, and power steering pumps. Know the alignment angles: caster (steering axis tilt, affects returnability and lead/pull), camber (wheel lean, affects one-sided wear), toe (total and individual, the primary tire-wear angle), and thrust angle (rear axle alignment relative to the frame).
Diagnosis by symptom
- Feathered tread edges = toe misadjustment.
- One smooth inner or outer edge = camber.
- Cupping or scalloping = worn shocks or out-of-balance tire/wheel.
- Lead or pull with a straight steering wheel = caster split or a dragging brake, not toe.
- Wander = loose steering components, low caster, or air suspension ride-height error.
Traps
The exam likes to blame caster for tire wear - caster mainly affects steering feel and pull. It also tests that ride height must be correct before an alignment, and that a vehicle with air suspension must be at normal ride height when measuring.
Worked example
Left toe reads +0.15° and right toe reads −0.05°. Total toe is +0.10°, but the individual values are unequal, which off-centers the steering wheel even though total toe looks small. Set total toe to spec and split it evenly so the wheel is centered.