Vehicle Body, Paint and Trim
Vehicle Body, Paint and Trim
This domain tests body construction, panel repair, paint preparation and refinishing, and trim fasteners. Expect unibody and body-on-frame construction, crumple zones, high-strength steel, panel alignment, fillers, primers, basecoat/clearcoat and paint defects.
Core rules and concepts
- A unibody integrates body and frame; crumple zones absorb crash energy. High-strength steel has repair limits and may need controlled heat or replacement.
- Body-on-frame vehicles use a separate ladder frame. Panel gaps and flushness are set with hinges, shims and clamps.
- Surface preparation is critical: clean, strip, sand and prime. Never paint over wax, oil or silicone.
- The refinish system is primer, basecoat and clearcoat. Follow mix ratios, pot life, spray distance and flash-off times.
- Defects include orange peel from poor atomisation, runs from too much material, fish eyes from silicone or oil, and solvent pop from trapped solvent.
- Trim uses clips, fasteners and adhesives. Airbags, sensors and wiring often sit behind trim, so disable systems before removal.
Worked example
After refinishing, small crater-like defects appear across the panel. Reasoning: these are fish eyes, usually caused by silicone or oil contamination on the panel or in the air line. Do not simply add more paint. Clean with approved prep, replace air-line filters, use fish-eye eliminator only as directed, and test on a spare panel.
Traps that cost marks
Applying excessive body filler; sanding through the e-coat; painting over wax; using the wrong reducer; and removing trim without disabling an airbag.
Key points
- Unibody and body-on-frame constructions differ.
- Crumple zones absorb energy; high-strength steel has repair limits.
- Clean and prime before basecoat.
- Fish eyes indicate silicone or oil contamination.
- Disable airbags before trim removal.