Heavy Vehicle Chassis Modification Certification – Section H (VSB6)
Get Certified for Chassis Extensions, Repairs, Axle Relocation & Trailer Frames
🧰 What is Section H?
Section H of VSB6 governs modifications to the chassis of heavy vehicles and trailers, including changes to wheelbase, rail reinforcement, axle relocation, chassis repair, and trailer frame alterations. These structural modifications are safety-critical and must be designed, documented, and certified by an Approved Vehicle Examiner (AVE).
AutoCert provides engineering inspection, design review, and compliance certification across all H1–H5 modification codes under Section H.
🔧 Section H Modification Codes
| Code | Modification Type |
|---|---|
| H1 | Wheelbase extension outside OEM options – chassis rail splicing, axle relocation |
| H2 | Wheelbase reduction outside OEM options – chassis shortening and axle relocation |
| H3 | Wheelbase changes within OEM options – only if approved by the vehicle manufacturer |
| H4 | General chassis alterations – frame reinforcement, repairs, damage recovery |
| H5 | Trailer chassis modifications – frame extensions, cross-members, repairs, accessories |
✅ What Requires Section H Certification?
- Chassis extension or shortening beyond OEM options
- Splicing or joining chassis rails
- Axle or suspension relocation
- Installation or removal of cross-members
- Trailer chassis frame repairs or structural modifications
- Body mount changes that require reinforcement
- Chassis strengthening for GVM or GCM upgrades
- Alterations around suspension hangers or tow couplings
📏 Design Requirements – Summary
- Maintain original cross-member spacing, or strengthen as required
- Use angle or channel reinforcement, and ensure correct overlap (typically 2× chassis height)
- Avoid cutting or welding near flanges or highly stressed areas
- Ensure all chassis materials match or exceed OEM strength
- Reinforcements must be tapered at 45° or frog-mouth profile
- Bolted joins must use high tensile ISO 8.8 or 10.9 fasteners
- Cutting and welding must follow AS 1554 Structural Steel Welding SP
- Avoid welds in heat-treated zones unless approved by OEM
🧪 Chassis Stress & Reinforcement Calculations
All chassis modifications must demonstrate:
- A Factor of Safety (FoS) of ≥3 for road vehicles
- A Factor of Safety ≥5 for off-road, tippers, and special-use builds
- Stress analysis must consider load distribution, CoG, axle mass limits
- Reinforcement sections must meet minimum section modulus requirements
AutoCert performs:
- Section modulus calculations
- Bending moment analysis
- Reinforcement selection (internal channel, angle, box section)
- Load diagrams and weight distribution evaluations
🛠 Examples of Work We Certify
- GVM-upgraded 6x4 to 8x4 conversions
- Wheelbase changes for crane/tray/tipper body installs
- Trailer chassis frame extension with twist lock fitting
- Monocoque chassis repair for livestock & fuel trailers
- Dog trailers with rear hanger reinforcement
- Bus/coach subframe restoration after corrosion damage
🧱 Chassis Joins, Cutouts & Repairs
- Joins must avoid spring hangers and high-stress areas
- Chassis rail welds must be continuous and grind-finished
- Cutouts (e.g., for engine swaps) must include reinforcement if >50% flange is removed
- Cracks must be drilled at ends and re-welded with reinforcement
- Heat-treated chassis require special welding or must be replaced
🔩 For Trailers (H5)
- Maintain chassis strength during cross-member removal or body mount changes
- Ensure correct point-of-articulation to suspension distances
- Avoid over-stiff cross-members (e.g. RHS or pipe sections) unless verified
- Ensure compliance with AS2809 and Dangerous Goods Code for road tankers
- Kingpin and twist-locks must follow VSB6 Section P if fitted
🧠 Why Choose AutoCert?
- ✅ RPEQ Certified for heavy vehicle chassis analysis
- ✅ Experienced with H1–H5 certifications
- ✅ Calculations & drawings included
- ✅ Full mod plate issuance & paperwork
- ✅ Mobile inspections across SE QLD