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How to Repair the X-Member on a Corvette C1 Frame

The X-Factor

Gerry Burger Feb 23, 2015
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Like so many old Corvettes, our ’60 has an incomplete, yet colorful history. Sometime around 1969 through 1974 the car was converted to a race car. Now, we use that term loosely as the stock rearend remained in the car and there were no visible suspension modifications other than a set of nicely homebuilt “slapper bars” for the rear springs. What did make it a race car was the big-block engine dropped between the framerails.

Remember, this was done during a time when you could throw a big-block in almost anything and have fun racing at the local track. The formula for speed was simple, small car, big engine. And so our ’60 received a big-block transplant. To facilitate the large engine and obligatory long-tube headers the leading portion of the X-member was unceremoniously torched from the frame. When we purchased the car, the engine and transmission were long gone, leaving two ugly stumps protruding from the frame. In fairness to the builder, they did an admirable job of relocating the steering box and, happily, did not damage the frame further.

After removing the ’60 body from the frame we set about repairing the X-member. Your favorite Corvette supplier can supply you with a pair of original-style front legs, which would be a simple way to repair the frame, and the only way to repair the frame if the car is being restored. Since this is not a restoration project we decided to fabricate a solution using 1/8-inch wall, 1x1-inch square tubing. We selected this material for several reasons, including the ease of working with the square stock, strength, and finally, the good looks of two tubes running up to the frame, giving the chassis a modern, performance oriented appearance.

Beyond wanting to fabricate our own solution, this repair process also allowed us to leave the two original body mounts in place. We have seen frames where these two front arms are simply eliminated and a new body mount is fabricated from the side rail inward to the proper location. This may be fine, but it has been my experience that Chevrolet rarely includes more than is required, so I figure if Chevrolet engineers thought this was a required piece it is probably best to include it in the finished frame design.

The front portion of the X-member does several things, not the least of which is providing a body mount. It also serves to stiffen the frame. By connecting the main X-member to the front of the side rails this provides a very rigid mounting point for the body and also resists the torque of the engine.

After a quick trip to our local steel supplier we were armed with two 10-foot-long pieces of 1x1-inch square tubing. No, it won’t take that much but we like having extra tubing around the shop and it was cheaper to purchase a full length. After trimming the torch-cut pieces from the original X-member we measured the distance from that cut to the point on the framerail where the box tubing would attach. We determined 29 inches would work but cut the piece a tad oversized so we could trim it to fit later.

The next problem was how to contour the box tubing to keep the upper profile below the framerail. This turned out to be quite simple. Using our hydraulic press we measured approximately 12 inches from the front and made a mark. Then we made two other marks 4 inches in either direction from this initial mark. With the tubing in our press we bent the tubing down between two pieces of 4x4-inch wood. This being a trial fit, we bent it a little, test-fit the piece, and then bent it some more. Once we were satisfied with the bend we used a Sharpie to make a mark on the press rail. After the initial bend, we moved outboard and added more arc to the tubing at the marks we scribed earlier, 4 inches to either side. After each bend we added another Sharpie line to our press rail. In the end we had a gently sweeping piece that followed the profile of the chassis, ensuring we would not have unwanted body contact. Making the other three pieces went quickly because we had the measurements for the pressure points on the tubing. By jacking the press down until the appropriate line was exposed on the press rail we had four identical pieces of box tubing. Making four of anything the exact same is always cause for celebration in my shop.

Next, we had to fit the tubing to the chassis. The front edge of each bar was cut on a long angle to meet the framerail and carefully fit to the inside of the frame. Fitting the rear of the bars was a simple matter of clamping them to the original channel stubs on the frame. We worked one side at a time and after clamping two bars in place we measured to ensure the bars were perfectly parallel. This is more important for aesthetics than performance. Once again we were pleased (amazed?) that the bars were both identical and parallel. It was decided a center brace should be added for strength, so two pieces 1 3/4-inches long were cut and tack-welded in place. We then carefully removed the two bars and clamped them to the welding table before finishing welding.

With the two pieces of tubing connected by the center brace we returned and clamped it in position and did the final welding to the framerail and to the original piece of channel coming off the X-member. This completed our repair and we are pleased with the results. The piece of channel will not be seen as the body covers that portion so the only thing in the engine bay will be the pieces of box tubing, making this a strong and good-looking repair.

It should be noted that all of this was done in my admittedly well-equipped home garage, and should be well within the reach of many home shops. Next up is replacing the rusted rear crossmember followed by changing the front and rear suspension, so stay tuned as we continue our homebuilt C1 chassis.

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01. The front “legs” of the X-member had been chopped off somazetime in the early ’70s to make room for a big-block engine. After spending a few days in our home shop our chassis was repaired and looking good.

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02. Race car technology of the backyard racer was not always fancy. We offer the torched-off stubs of the front legs of the X-member as exhibit A. The square pad on top of the stub is a body mount.

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03. Both sides of the frame had received a similar fate. We had the frame hydro-glass blasted to ensure good clean metal for welding and to examine the entire frame for rust or defects.

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04. Using a square, we scribed a line and then carefully cut the end of each stub nice and square. Just getting rid of the ragged cut was a step in the right direction.

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05. Up front, on the inside of the framerail the remains of the original channel-shaped member were left on the frame. After taking this photo, we cleaned up all of the slag from the torch cut. Our new member will mount to this pad.

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06. We opted for 1x1-inch square tubing with 1/8-inch wall to fabricate the new X-member legs. A port-a-bandsaw makes quick work of cutting steel.

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07. To ensure the tubing does not interfere with the body it must have a contour bent into it that matches the framerail. We used this basic press and a two blocks of wood to bend the tubing.

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08. After the initial bend we moved outward 4 inches in both directions from the center bend and added more curve to the tubing until we had the desired contour. It required three bends total.

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09. After we made each bend (center, 4 inches left, and 4 inches right) we marked the leg of our press with a Sharpie. Then the three remaining legs were easily bent down to the marks, making each piece identical.

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10. After carefully shaping the tubing, we test-fit the tubes to the chassis. It pays to have a number of large C-clamps handy for this job. Satisfied with the two pieces we decided to add a center brace.

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11. After cutting a piece of 1x1-inch square tubing 1 3/4-inches long we tacked it in place while the tubing was clamped to the chassis. Then we removed the piece and clamped it to the welding table for final welding.

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12. The center brace was welded in place using our Miller Syncrowave 200 TIG welder. A MIG welder could also be used for this job.

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13. On the open end of the upper piece of tubing we cut a small piece of 1-inch flat stock and welded it in place to close the tubing.

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14. With the center brace welded in place, we fit and clamped the piece to the chassis side rail. Take your time and fit the welding gaps perfectly for a strong joint that is easy to weld.

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15. We tack-welded the piece in place and then TIG welded it to the side rail. We clamped both sides in place and alternated welding from the passenger side to the driver side to minimize any chance of warpage.

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16. Next, the rear of the new bars were welded inside the original channel. Once again, the welding was staggered to prevent heat from pulling or warping the channel. There is no need for full welding here, hence the stitch-weld pattern.

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17. And here’s the completed assembly welded in place. The square tubing is stronger than the original channel and gives the frame a bit of a modern tube chassis appearance.

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18. After a couple of coats of self-etching primer the chassis is really looking good. The original channel portion will be hidden by the body so only the square tubing will be visible from the engine bay.

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19. We like the idea that the original body mount is in the exact location with the factory-style pad in place. The new tubing will provide a very stiff mounting point for the body, and we all know how important that is with a fiberglass body.

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20. And here’s the finished product. The camera tends to visually bend the bars, but look at the right-side bar and you will see it is straight out of the channel, but bent down to match the upper profile of the framerail.

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