Frame, Unibody, and Structural Straightening
Frame, Unibody, and Structural Straightening tests measurement, anchoring, pulling, and repair limits. Structural repair is a measured process, not a visual one.
Measuring and setup
- Use a three-dimensional measuring system or OEM datum points; compare to OEM dimensions.
- Anchor the vehicle at the specified points so pulling does not drag the whole body.
- Support the vehicle at ride height or the specified bench position.
Pulling
- Pull in the direction of the original impact and in stages; over-pulling stretches metal.
- Use clamps and chains aligned with the load path and inspect for slippage.
- Stress-relieve with controlled heat only where the OEM permits; many UHSS rails prohibit heat.
- Re-measure after each pull and check gaps, doors, and glass fit.
Repair limits
- Section only at OEM-approved locations; use the specified joint type and corrosion protection.
- Replace rather than straighten heavily kinked or torn rails, crush zones, and mounting points.
- After structural repair, check wheel alignment, ADAS, and SRS.
Worked example
A front rail is 12 mm out at a control point. Reasoning: pulling the rail without anchoring the rocker will move the whole body and give a false reading. Anchor at the OEM points, pull in small increments, re-measure, and inspect the apron and strut tower. If the rail is kinked at a crush zone, replacement is correct, not more pulling.
Traps
- Pulling to eyeball alignment.
- Heating a high-strength rail to relax it.
- Measuring only one side.
- Skipping post-repair calibration.