Homebrew Subframe Connectors
Part II
At this point, you should have the car up on jackstands, everything should be electrically isolated , have collected all the necessary materials, and be ready for the actual fabrication process to begin. Let me point out that there are several versions of the same theme available to you. I will highlight some of your options along the way and offer you drawings that detail some of these elements.
If I had it to do over again, I would probably do two things different. One, I would do seat brackets similar to the Kenny Brown Super Subs mentioned in Part I. Second, I think the full length style offers more for your money and time. Responses from people who have experienced the results of both have been such that I really see no reason to not go ahead with the full length using full size 1-1/2" x 2" tubing. Having said that, the following instruction is based on connectors that only go from the transmission crossmember to the torque box area. You should be able to modify any details for the full length easily when necessary. Diagrams for both are presented.
Drawings
Chris Neighbors has supplied a set of drawings detailing the measurements for the fabrication of either full length or regular length connectors. I will refer to them in the following text. Click on a link and a new window will open containing a full size view.
Getting Down to Business
Step 1: Cut a piece of tubing the approximate needed length.
The first thing to do is cut a piece of tubing that is long enough to span the length, but short enough that you can handle. I cut mine about 48" but make sure you do not go too short. Full length connectors will probably need this cut to be around 5'6" (compare the measurements of the figures with actual measures under the car.). Also, you will want the front of the connector to be at a 45 degree angle so this would be a good time to make that cut also.
Step 2: Seatmount brackets.
The floorpan area around the two rear bolts for the front seats is prone to cracking. To prevent this, the addition of seatmount brackets is highly recommended. As already mentioned, if you copy the Kenny Brown style you must do them before you weld the connector to the car.
Examine fig 3. Notice the seatmount bracket is simply a piece of 2" x 2" tubing cut into two lengthwise pieces. Measure down from two diagonally opposite corners 5/8" then use a straight edge to make marks along the length of the tubing (see the drawing for clarification). For the holes, double check the center to center distances for the seat bolts on your car, then drill two 9/16" holes centered on the top of the bracket. Cut the notch for the bracket to sit on the tubing 5/16" deep and 2" wide. You may need to modify them a little when you test fit them later. Note that the notches have different measurements for passenger and driver's side.
Step 3: Bend the tubing using cuts made through all but one side of tubing.
In order to facilitate an easy attachment, clear the floorboard, and keep ground clearance at a maximum, the tubing is bent at two places. This makes a Z-like shape with the front of the connector being higher than the rear. Finding a square tubing bender is not easy, plus they distort and weaken the material to the point that your best option is to make cuts through what will be the inside surface of the angle down through the sides, leaving the surface that will be the outside of the angle (see fig. 1 and/or fig. 2). You can do this either with a chop-saw or a hand held cutoff wheel (or even a hacksaw if you are persistent) but make sure you keep the cuts square with the tubing.
- A 5/64" wheel thickness produces about a 4° angle when the cut is closed up for the regular length connectors.
- A 7/64" wheel thickness produces about a 4° angle for the full length.
However, the best way to know if you have a wide enough gap is to make a cut, then test fit the piece to the car. You can take more out of just the top of the cut by closing the gap while recutting therefore keeping the gap as small as possible to make welding easier. Measurements for placement of the cuts can be found in figs. 1 and 2 but you should get a close verification by measuring your car directly. So far, the measurements in the drawings have worked fine on a variety of models and years.
Step 4: Tack it all together
When your angles are right, bolt the seatmount brackets to the car using the M10-1.50 nuts and flat washers. Hold the connector in place with a jack, and/or a friend and check the fit of the notch in the seatmount bracket where it slides over the tubing. Trim as necessary. When everything fits nicely, tack the tubing together (not to the car) at the gap for it to hold its shape. Also tack the seatmount bracket to the connector.
You should have something similar to this:
Step 5: Weld up the gaps, close off the front (angle) end, and cut the back to length.
With the connectors out from under the car and the angles and seatmount bracket tacked, finished welding the gaps. You should clean up the welds with a grinder.
This is also a good time to cut a piece of the 3/16" (or 1/8") plate and weld shut the front of the connector (where you cut the angle). Make it smaller than the outside of the tubing (but of course not where it falls inside) to allow easy welding. If you get a little carried away and some of the weld is above the top of the tubing, grind it down flush. You will want the tubing to sit as tight as possible to the car's subframe. Also, I left the rear open for tying in with the future torque box reinforcement plate. It will have a tab bent down that will be welded on, closing off the back of the connector.
Hold the connectors up to the subframes and mark the rear to be cut off. I left mine about 3/4" back from the notch for the lower control arm. This was to allow a little room for the aforementioned plate to reside and tie off to the torque box better.
Now you have something like this:
Full Length with seatmount brackets welded and ready
Step 6: Prep and paint.
While you will want to paint the connectors once they are on the car, coating the top and other surfaces is almost impossible once installed. So I painted them thoroughly before welding them on. This also cuts down on how much area you have to cover laying on your back in a cloud of paint fumes. You can, and should, grind away any areas that you need to weld. If you are using the 3M weld-through coating (highly recommended), spray this on the ends where you are going to weld ( or even the whole thing) before you paint it. Then you can just paint the main body and leave the ends for later. The 3M stuff makes a zinc coating when welded through so it will be protected from rust. Make sure you clean the surface well of any rust and wipe them down with laquer thinner prior to painting.
Step 6: Weld them on!
Welding warnings: Do not concentrate your heat too much in one area. It is better to make smaller welds and then fill them in. Excessive heat can ruin the car's subframe, plus you take a chance of blowing through the relatively thin metal. Also keep in mind the interior of the car at all times. If you have not removed the carpet, make sure you don't catch it on fire. This is especially true when adding the doubling plates later and welding the seams around the torque box. I HIGHLY suggest you remove the carpet in the areas you are welding. If you burn your car down, just remember I warned you.
Carefully align the connectors on the subframes and hold them firmly against the car with jacks. Bottle jacks really work well here. Just be careful and do not jack the car up. You do not to impose any unnatural stress on the chassis when you weld the connectors on. Also, remember to make sure the seat mount holes line up. Go ahead and bolt them on tightly to the car. Weld all joints between the subframes and connectors using skip welds in approximately 1" to 1-1/2" long beads, alternating connectors and sides (inside/outside) to avoid warping and blowouts. Continue skip welding until the entire seam (where physically possible) is completed and appears continuous.
This is a good time to weld up some of the seams on the torque box too, being that you are already under the car with the welder.
Step 7: Adding the doubling plates.
Now you need to add plates to the sides of the connectors that tie the subframe to the tubing. The idea is to create more area to transfer the load across the surface of the two components. This makes it stiffer and also prevents fatigue on the subframes.
You might notice that my front plates are fairly large. It may be a little overkill, but it cleaned up the transition and allowed a much larger area to be welded. This was important because I did not follow the exact order that I have outlined here. I welded the plates onto the connectors, then welded the plates and connectors as a unit to the subframes. No matter how you make the plates, I suggest welding the connectors on first, along their entire length, then adding the plates. It should allow for a much stronger connection. If you want to make front plates that resemble mine, get a piece of cardboard and cut a template that follows the contour of the floor and slightly above the bottom of the connector. I found that all four front plates (inboard and outboard) were the same. Double check your template against each place to verify on yours. At the very least, you want 2" x 3" plates on the front and you can go as large as you like on the inside back with 3" x 4" being a good minimum.
Drill two 1/2" holes, centered on the plate, one so it hits the center of the connector and one so it hits the center of the subframe. This will allow you to weld the center of the plate to each component.
I left off the plate for the rear outside. I plan for the torquebox reinforcement plate to wrap around and serve this purpose. Thus, the subframe, connector, and torquebox are all tied in together. If you want to go ahead and add a plate, you will need to bend one at a 90 degree angle. Something, at least 3" x 3" bent into a 90 degree angle should be sufficient. Add holes here also for welding the center.
Weld all the plates completely around their perimeter. Make short welds as before, being careful not to concentrate too much heat in any one place, when you weld to the car's subframe. This is especially important if the interior is still in the car. You are very close the interior at the top of the subframe. Be careful.
Here are some closeups of the front plate installed. (Note I did not add holes but I highly recommend them).
You can see the back here:
Step 8: Final cleaning and painting.
Well now the hard part is over. All that is left is to clean up any wild welds with the grinder and shoot some paint on your killer new subframe connectors. After you finished cleaning the welds, sand off any rust and wipe everything down with lacquer thinner. Paint until your satisfied but make sure you cover all bare surfaces.
That's it. I hope everything was clear enough. If you have any questions please feel free to email me or Chris Neighbors.
Thanks to...
This project would not have been possible without the generous help of Chris Neighbors and John Pyle. Chris has taken considerable time and effort to create the drawings and design for the different styles and we all owe him a large thank you. He contributed a large portion of the writeup and I appreciate his eye for detail. John did all the welding for my connectors and I throw a big thank you to him.