Week 7 · Session 13
Visual Inspection and Systematic Fault Trees
60 min lecture + 60 min lab

Learning Objectives
  • Develop systematic inspection routines for 4×4 suspension
  • Identify failure modes from visual cues and tyre wear patterns
  • Build diagnostic fault trees that prioritise by safety criticality
  • Understand component lifespan and how desert conditions accelerate wear
Static and Bounce Checks

Bounce test: Push down firmly on each corner and release. The vehicle should return to ride height and settle within 1–1.5 oscillations. More than 2 oscillations = worn dampers. No bounce back = overdamped or seized.

Rock test: Push side to side at each corner. Clunks indicate worn sway bar links, bushings, or ball joints.

Ride height: Measure from wheel centre to fender lip at all four corners. Asymmetry indicates spring sag, uneven loading, or suspension damage. Compare to factory specs if available.

Dial indicator: For precision, use a dial indicator on ball joints and tie rod ends. Axial play exceeding 2 mm typically means replacement.

Tyre Wear Patterns as Diagnostics

Pattern Likely Cause
Inner edge wear Excessive negative camber (common after lift without UCA correction)
Outer edge wear Excessive positive camber or under-inflation
Feathering (sawtooth) Toe misalignment
Centre wear Over-inflation
Cupping / scalloping Worn dampers or wheel imbalance
One-sided wear Camber or caster asymmetry

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Tyre wear is the most honest diagnostic tool. It tells you what the suspension has actually been doing over thousands of kilometres. Learn to read it.

Underbody Inspection Checklist

A systematic front-to-rear sweep under the vehicle. At each component, check:

Boots and seals — CV boots, ball joint boots, tie rod boots. Any tear = contamination and accelerated failure. In the desert, a torn boot is an emergency repair.

Bushings — Cracking, deformation, separation from metal sleeve. Rubber degrades faster in desert heat. Polyurethane lasts longer but develops squeaks.

Shocks — Weeping oil on the body = failing seal. A light mist may be acceptable; dripping is not. Check reservoir hose connections if equipped.

Springs — Visible cracks (fatigue), broken coils, sag (compare left to right ride height).

Mounts and brackets — Cracked welds, elongated bolt holes, corrosion. Shock towers on IFS trucks are a common fatigue point.

Steering — Play in tie rod ends, drag link (solid axle), rack boots, power steering leaks.

Component Lifespan — Desert Adjusted

Component Normal Life (km) Desert Factor
Rubber bushings 80,000–120,000 Heat + sand → 30–50% shorter
Polyurethane bushings 120,000–200,000 More durable; higher NVH
Heim joints (unsealed) 40,000–80,000 Sand ingress without boots is rapid
Ball joints 60,000–120,000 Bigger tyres + articulation accelerate wear
Coil springs 150,000+ Salt flat corrosion shortens life
Shocks (OEM) 80,000 Desert heat/cycling → 40–60k
Shocks (performance) 80,000–120,000 With regular service (re-valve, re-charge)
CV boots 100,000+ Heat + sand + flex = inspect every trip

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LAB
Full Underbody Inspection

  • Each student inspects a vehicle using the checklist. Document every finding with photos.
  • Use dial indicator to measure ball joint play.
  • Identify at least 3 faults on a prepared vehicle (pre-staged wear items).

QUIZ
Fault Identification — 5 Photos

Identify the fault, likely cause, and recommended action for 5 component photos.

ASSIGN
Used Vehicle Inspection Report

Perform a full inspection on a used 4×4 (your own or a friend’s). Document findings with photos. Prioritise repairs by safety criticality. Estimate cost for the top 3 repairs.


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