How to Build Your Own Subframe Connectors
NOTE: Proceed at your own risk, as the author of this article will take no responsibility for any damaging effects caused by following (or not following) the instructions herein. This article written by Ashentep, please do not copy without proper credit.
Tools/Supplies needed:
- 2 - 5' 2" long pieces of 2x1.5x.125" box steel
(with a 45 degree cut at one end of each)
- 1 - 14.5" long piece of 2x2x.125" box steel (should have the welding shop cut this piece long ways for you if you
dont' have a plasma cutter - details & plans in article)
- 1/8" sheet metal to make mounting tabs
- reciprocating saw, die grinder with cut off wheel, hacksaw, or something similar to cut 3 of the 4 sides of the long box steel
- drill and 1/2" drill bit + smaller bit to start the holes
- welder or at least access to one (as well as knowing how to weld well)
- floor jack & stands to hold car up by the SUSPENSION, and not by the frame...don't want to stress the frame while installing
- 1 or 2 bottle jacks or similar to hold SFC to chassis while fabricating - I
used the stock jack in the trunk, but a bottle jack would've been a lot easier
- paint to cover the welds once done
- having a friend to help hold the SFCs in place would be nice, but I did it alone, so you should be able to, too
What we're doing:
The stock chassis in Mustangs is really made up of the body. There is no real frame. There are what is called "subframes" in the front and rear of the car. You can look under the car and find these. The front has a rail that runs from behind the wheel well, to just in front of where the seat is at. The rear starts at the Torque Boxes, and runs up into the wheel well. These two subframes are connected by the rest of the body's sheet metal, not exactly what I woudl call a sturdy connection. What I did was build a set of connectors that welds to each of theses subframes and connects them together. Hence the term subframe connectors. This is article is less about what they are, and more of how to build them, so lets continute.
Other designs:
If you look at other popular designs, you'll notice two common styles: tubular and rectangular. Theres a lot of argument on which is better, but the differences should be so slight (not to mention the fact that the subframe connectors of either type are more likely stronger than the subframes they are connecting so who cares) that it should make next to no difference.
Most short subframe connectors are made of 2x1.5(sometimes 2)x~.0765-.125" wall thickness tubing, while the full length subframe connectors are of 2x1.5x.0765-.083" wall tubing. To be on the strong/safe side, I'm going to make a set of full length connectors out of 2x1.5x.125 box steel.
Also, for the bends, most connectors actually bend the box steel. This is bad for strength, and many have tabs that are welded in on the inside of the bend to correct this. Rather than bending the tubing, I am cutting and welding at the bends. A good weld is as strong, and usually stronger, than the surrounding metal, so this bypasses the need for any reinforcements at the bends.
Lastly, you'll notice many designs do, and many don't, include connectors that bolt to the seat bolts. This essentially cuts the length of the connector where it touches nothing in half. I'm including this in my design, but it is not necessary.
What you choose to do with yours is by all means your choice, so please don't copy me, just to be copying me.
Process:
1. Lets get started, shall we? I measured the length my connectors need to be at 5'2". Measure your chassis first before buying the metal. Once you get the length, make sure the box steel you bought is the right size, then we can start the actual building.
2. A note for some cars, there are braces/brackets for the transmission crossmember spot welded onto the subframe rails. These must be cut off or ground off for full length subframe connectors, to allow a better, flush fit.
3. Now, measure from the front of the front subframe, to the back of it. Add about .5" to this measurement, then mark this measurement on the box steel (measuring from the 45 degree cut). This is where you will cut through 3 of the 4 sides, leaving the top uncut (this is the side that will touch the chassis where the long side of the 45 degree cut is). Now, after marking the 3 sides to be cut, use the die grinder, cut-off wheel, sawzall, etc. to cut three of the four sides. Measure the cut width. It needs to be just under 1/8" to be wide enough to allow the angle of bend we need. Once you get that cut done, lets move on.
4. Now, for the second cut, bend the connector and spot weld it where the first cut was, then raise the connector into place on the chassis. Make sure it clears the chassis at all spots, but is very close, to allow ground clearance. Also, check to make sure its close to the seat bolts, so the cross member can be welded in place easily. You may have to break the weld and rebend/spot weld. Once you are satisfied with this, look at where the rear part of the connector is even with the height of the rear torque box. Make a mark at this point (14.5" on my particular connector), and cut through 3 of the sides, leaving the bottom this time. Same as before, just under a 1/8" cut is needed. Again, bend this in, and spot weld it.
5. Back under the car, put the connector in place. Are you happy with the fit? Does the front and rear sections of the connector fit flush to the subframe rails? If not, cut your spot welds, and rebend until they do, then spot weld it again. Once you've done this, lets start with the seat belt crossmember.
6. Have the 14.5" section of 2x2x.125" steel cut as this diagram shows:
7. Now, to prepare the cross member, depending on what side you're starting with, this is what you'll need to do:
a. The driver's side bolts are 11" apart, so 1.75" from either side, drill a small pilot hole centered in the width of the 2" side of the brace. Now exactly 11" from that hole, drill another hole centered in the 2" side of the brace. For the passenger seat, the bolts are 10 3/4" apart, so from 2" of one side drill a small pilot hole centered on the 2" side of the brace. Now 10 3/4" from that hole, drill another pilot hole centered on the 2" section of the brace.
b. Bolt the braces up to the seat bolts, with the long leg facing forward, then raise the subframe connector into place. There should be contact between the two. Mark this contact, and grind/cut the contact area down in ~1/16-1/8" steps until the subframe sits flush on the front and rear subframes and just contacts the long leg (and hopefully the short leg too).
c. Now with the braces bolted in place and connector raised to the exact position you want it to be in permanently, spot weld the seat brace to the connector. Now pull the connector out, and weld up the connector, and the three cut sides of the two bends.
8. Now measure both the front and end of the box steel openings, and make plates to cover these from the 1/8" sheet metal you bought. Weld these into place.
9. The build is done! Now on to painting and welding the connectors into place. Clean the connectors, then spray them with some paint to keep them from rusting. Now, Clean the subframes of the car of paint, as well as the sections the connectors will touch to get a good electrical contact. Raise the connector into place, bolt the brace to the seat bolts, and make sure everything looks the way you want it.
10. Weld the inside and outside of the connector to the subframe in short sections, alternating sides. This alternating will keep the carpet from burning in the car, as well as keep from burning through the subframes.
11. Make tabs out of the 1/8" sheet metal that will contact both the connectors, and the subframes, then weld them into place. This isn't necessary, but I think it will help, by increasing the surface area of weld connecting the two together.
DONE!
Heres some pictures of mine, and diagrams that may help:
Click to enlarge drawing
