Start at the axle
M35A2 2.5-ton and M939 5-ton Rockwell top-loader axles are familiar foundations for heavy off-road builds. Their size and gearing can suit demanding terrain, but weight, parts condition, braking and tire choice all affect the finished vehicle. Inspect used housings and drivetrain components before designing around them.
Portal boxes add reduction at the wheel and raise the axle housing relative to the wheel center. They also change scrub, leverage and packaging. The correct combination depends on the vehicle’s loaded weight, intended tire and the actual components used.
| Build element | What we look at |
|---|---|
| Rockwell axle | Condition, gearing, brakes and service access |
| Portal box | Reduction, clearances and component ratings |
| V-tread tire | Loaded diameter, weight and available clearance |
Locate the axle, then cycle it
A four-link controls axle movement through the suspension’s travel. Chromoly Heim joints offer adjustable connections, but joint size, misalignment, mounting strength and periodic inspection matter. We consider separation, link angles and available movement together, then check the complete range for binding and interference.
Steering and the space around it
Full-hydraulic orbital steering can simplify packaging on a purpose-built off-road machine. Cylinder placement, stops, hose routing and the loss of mechanical steering feedback need careful attention. Design for the use and applicable rules of the vehicle; a trail machine is not automatically road legal.
A cage is a structure
DOM roll-cage triangulation, sound joints and properly placed gussets tie loads into the chassis. Seat mounts, harness geometry, driver clearance and the ability to get out all deserve room on the drawing before the final tube is welded.