Straight cracks (1) normally start from the edge of a flange. The crack travels across the flange and through the web section of a rail. The crack continues through the other flange. Straight cracks result from high concentration of stress in small areas of the frame, excessive bending movement, and torsional loading.

Sunburst cracks (2) radiate from a hole in the web section of a rail or crossmember. Sunburst cracks are caused by high loads at a mounting bracket or a crossemeber that is not securely attached to the rail.

If cracks occur to both the rail and reinforcement at a particular area of the frame, the cracks must be repaired separately. The flanges must react independently in order to prevent localized stress concentration. Use a copper spacer between the flanges of cracked base rail flanges and reinforcement flanges.

Crossmember mounting flange cracks may be repaired in the same manner as side rail cracks. However, weld bead should be built up in order to provide a smooth radius. Replace a crossmember that is badly damaged.

It may be necessary to align the frame and level the rails before you repair the frame.

1. Remove any equipment that will interfere with access to the crack.
2. Locate the extreme end of the crack and drill a 6 mm (0.25 in) hole.
3. V grind the entire length of the crack from the starting point to the 6 mm (0.25 in) at the extreme end.
4. Open the bottom of the crack 2 mm (1/16 in) in order to allow good penetration of the weld.

Use a hack-saw blade.

5. Weld with the proper electrode and welding techniques.
6. Grind the weld smooth on the inside and the outside of the rail or crossmember. Be extremely careful to eliminate weld buildup or notches on the edge of the flange.