The following demonstrates our procedure in repairing a Corvette frame. There are many factors involved. We have chosen this job, a 1958 Corvette, to publish because it involves structural considerations and how to perform the repair while supporting the frame properly.
tools needed: You'll
need particle mask, goggles, grinder, three inch cut-off tool, torch, mig welder, large clamps, hammer, undercoat, and magic marker.
Begin by jacking up the car and placing jack stands just forward of the rear wheels. (ill. 2). While this placement of stands allows for access to suspension components for removal, it causes the rear area to hang. This is evident by an increased door gap to rear quarter at the top of the door. Very Important: The rear crossmember must also be supported. Jack up the rear crossmember and shim its jack stand as necessary until the door gap looks normal, (3/16 inch). Notice (ill. 7).
Remove suspension components leaf spring u-bolts, shock nuts, and shackles. Given the age of this 1958 Corvette, special care is given to the removal of old rusty nuts and bolts. First clean the threads using a wire brush (ill. 1). Heat the nut until it sustains a red color with a torch. This will expand the nut, breaking the corrosion bond between the bolt and nut, works every time. Remove the nut while it is red hot. Since the nut is now softer, its threads will remain in tact as it traverses the now wire brush cleaned u-bolt threads. Skipping the wire brush cleaning will almost always strip the nut threads.
Prepare repair area by grinding all rust well beyond the rot whole. The repair plate must be welded to good solid steel. These frames were .100 inches thick when new, therefore the repair plate needs to be welded to steel at least .080 inches thick. Drill small (1/8 inch) exploratory holes if in doubt. Mark proposed repair plate with a magic marker. Make a paper template by tracing it over the marked out site. Cut the paper template accurately and trial fit on the repair area. Paper is much easier to trim than steel. As in most repairs of this nature, a side plate and bottom plate are required. Allow 1/8 inch clearance between these plates when fitting and plan for a briging type weld. This method will create a radius shape like the original as well as a bond to whatever original frame corner might be left. Trace the paper template on the steel and cut. Hint: When the utmost accuracy in cutting steel is desired, cover the steel with masking tape and trace the template using a pen. For this job we used 1/8 inch steel for the side plate and .090 inch for the bottom. Cut the steel with a thin cutting wheel. Fit and trim the steel repair plate(s) as necessary. Position steel repair plates on the frame, clamp into place, then weld(ill. 3). A 100% weld bead is not entirely desirable. A few small weld voids will provide for a little frame flex.
Prepare the repair area for painting or undercoat by grinding the welds and entire repair area. Wire brush the welds also. Grind the corner weld to a radius shape. Apply finish wether it be undercoat or more elaborate body filler, prime and paint (ill. 4).
Prepair additional repair areas as done previously. This car's rear crossmember had some rot only on the left side (ill.5). Since the car is a driver we thought it prudent to do a repair rather than replace the entire crossmember saving the customer some serious money. Oddly enough, the last two crossmembers we replaced on this vintage Corvette had less severe rot but was spread from side to side. We decided to cap the end of the crossmember with the fabrication of four plates, bottom, front side, rear side, and one inside shackle the support. All surfaces were ground and wire brushed. We even sand blasted the inside of the shackle support. The plates were positioned, clamped, and welded. All welds were ground. New surfaces were ground and wire brushed as were all welds. The repair area was then undercoated (ill.5). The entire crossmember was also cleaned and painted (ill.6).
1. Wire brush rusty threads