Multi-Pull Sequence for a Diamond in a Unitized Sedan
2018 unitized sedan with a right-rear 35-mph impact. The right rear rail is 22 mm short, the left rear rail is 4 mm short, and the rear crossmember is shifted 12 mm to the right. The right rocker has an 8-mm buckle, and the trunk floor is wrinkled. The right quarter panel is crushed. The vehicle is on a frame rack with pinch-weld clamps. A technician proposes one 6-ton pull on the right rear rail toward the left and front to square the body. The OEM says the rear rail is 590-MPa HSLA and may be cold-pulled, but the rail has a kink at the suspension mount. The shop has a computerized measuring system.
1. Develop an anchoring and pull plan. Is the proposed single 6-ton pull appropriate?
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A single 6-ton pull is too coarse. The damage is three-dimensional: the right rail is short, the crossmember is shifted right, and the rocker is buckled. Anchor the vehicle at the opposite rear pinch weld and at mid-body points, using multiple clamps. Plan a primary pull rearward to restore rail length and a secondary pull left to square the crossmember, with measurements after each pull. Use low, controlled force and monitor for new kinks. The kink at the suspension mount changes the plan: that area is a candidate for sectioning or replacement, not continued pulling.
2. What pull sequence and measurement checks should be used?
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First relieve the trunk floor and rocker with a light pull, then pull the right rear rail rearward in stages, measuring rail length and crossmember position after each 1–2 tons. Next apply a lateral pull to correct the 12-mm crossmember shift. Check the left rail and roof rail for movement. Stop when dimensions are within OEM tolerance or when a kink, crack, or suspension-mount deformation appears. Do not use heat on 590-MPa HSLA unless the OEM permits it. Re-measure after releasing tension because the body may spring back.
3. When should the technician stop pulling and replace or section the rail?
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If the rail kink at the suspension mount cannot be removed within tolerance, replace or section the rail at the OEM location. A pulled rail with a remaining kink will not perform in a subsequent crash. Verify suspension mounting point dimensions and check for cracks after pulling. Document pull forces, anchor points, measurements, and any sectioning. Corrosion protection and weld quality also need confirmation. If the crossmember or floor pan cannot be squared without overloading the rail, revise the plan rather than increasing force.