Subframe Connectors

With the toe boards welded I was able to move rearwards to the floor pans. But until they would be installed, the subframe connectors would be designed, manufactured and installed first. I ended up with designing them myself as I wanted them to look like they were part of original structure, instead of bolted on later.

The seat platforms were removed, the frame rail extensions were exposed and by using the masking tape I sketched the plan. The old floor pan was held in place as long as possible as a guide for positioning the connectors. The connectors would be made of 60x60x2mm square tubes which would fit tight in the extensions. I obtained two tubes of 1800mm in length. The inner surface of the extensions themselves appeared to be in excellent condition.

The front and rear rails are neither in line or in same height which demands for making a couple of pairs of corners if you want them to follow the contours of the floor pans. An application of this kind of solution can be found in DazeCars website. Their solution looks good, but it not exactly what I was looking for. Therefore I took some measures (could not find good documentation in the web) and sketched the shape with masking tape.

I later found BuckeyDemon's thread at www.1969stang.com showing the best looking subframe I've ever seen on a Mustang.

Sketching the shape of the connector

I measured the distance of how far the inner surface of the frame rail is from the rocker panel and decided that the lateral corners would have to result to connector moving 87 mm out when travelling to rear. To make that kind of movement within the sketched length required two 25 degree angles.

Extension rear end was cut off

25 degree notch cut off

After the first cut was tack welded I aligned the tube with the edge of my work bench so that the position of the second notch could be exactly defined. The notch should be made where the tube has traveled 87 mm out of the table's edge. When this was defined and the notch cut, the tube was then clamped to the table and with the help of wood blocks twisted so that the needed 87 mm was obtained and that the front and rear were still parallel with each other.

Defining the position for the second notch

Tube aligned and tack welded

The front end was then narrowed so that it creates a wedge to make it easier to slide under the toe board towards the frame rail. I measured and marked reference points to the old floor pan and the tube to help me observe how far the tube has to go under the toe board to meet the frame rail.

The wedged front

Now that I had the reference points for longitudinal position I would be able to test fit and define the needed position and shape of the cutting still needed. I cut off the top of the tube from the area that is in the rear foot well. The remaining thickness in this area is 38 mm. The rear of the tube was shortened with 20 cm as it appeared too long. I copied the shape of the bottom of the rear torque box to the side of the tube and made necessary notches. At this point I was confirmed that no vertical notches were needed.

With these modifications the tube appeared to fit with some hammering. It's easy to hammer it in but it's painful to pull out when done so at this point I prepared the frame rail extension by drilling the holes for spot welding and painted the areas which would be not accessible later.

The next day I slid the tube in , helped the moves with some tender hammering and the tube was there ready to be welded. About 15 spots were welded to the both sides of the frame rail extensions and the rear edge of the frame rail extension was seam welded to the connector. In the rear the connector was seam welded to the bottom of the torque box and to the inner edge of the read frame rail.

Positioned and ready to be welded

Spot welds along the frame rail extension

I did not pay too much attention to detailing and finishing the tail of the connector at this point. It is much easier to work with later when the leaf springs are removed and the car is hung on the rotisserie.

Seam welded to the torque box

The detached top of the rear part was then cut to fit the top again and placed on top of opened area. With the top back on this area is 60mm x 40mm in size. Before this I had verified the correct vertical position so that it would align with the floor pan as close as possible. I accepted the top part to be a couple of millimeters higher than the floor pan so it could be welded on the torque box front as well.

The rear of the connector boxed

Finished

Now the remaining old floor pan could be removed. The connector penetrates in to the cabin but only in the area which will be covered with the seat platform. I added some seam welds between the upper edges of the tube and the inner edges of the flanges of the frame rail extension. The tube is now surely strongly attached and stiff. The rest of the floor pans was removed and some primer was spread.