Subframe connectors - Scratch built thru the floor

[femtnmax]

I had bought US Cartool connectors, but my 74 Chally had large humps in the floor just aft of the trany cross member, and the overall connector fit was poor, so decided to make my own.  Material cost was under $60.  Labor, well, my labor's free.
OEM metal gage thickness using Miller stamped steel gage included:
Rear frame:  14 gage  (0.075)
Trany Crossmember:  14 gage
Floor:  20 gage  (0.026)
So I selected box tubing 0.085 thick, rather than 0.125 thick.  Having similar gage thickness should help avoid hard points in the frame where cracking could form.
Material included:  (2 of each required)  All measurements in inches.
Box tubing:  3 x 1 1/2 x 42 3/4 x 0.085
Front plate:  4 x 3 1/4 x 1/8
Front strap:  3 1/2 x 1 1/4 x 1/8
Rear outboard vertical spacer:  3 1/2 x 1 x 1/4
The OEM rear frame of the car does not run true with the length of the car.  IE not perpendicular to the rear axle, so the box tubing needs a taper to match up to the rear frame.  I cut slots in the aft end of the top and bottom of each tube.  Total slot length was 3 1/2 inches.  Slot width was 1/8 for the first 2 1/4 inches, the remainder is 1/16 wide.  I clamped the end of the tube, brought the 1/8 inch gap down to less than 1/16 and welded the gaps closed, and ground the welds flat so tubing would slide easily into OEM existing rear frame box.
The outboard spacer was to take up the clearance between the new box tubing and the width of the existing frame box.   I thought about using wider 2x3 tubing, but decided against it as it has it's share of compromise to decrease the 2 inch width enough for the new tube to slip inside the OEM tube.   
Note that the add on frame connectors weld to the underside of the existing frame, and have a much reduced vertical cross section as compared to the original frame.  So they have their fair share of compromise in ability to resist bending.
The front plate is welded to the front of the new box tubing, and has 5 holes 1/2 diameter (3 one side, 2 the other side of the box tube that will be welded/filled to the back side of the trany cross member.  The front strap welds to the underside of the front of the new box tubing, similar to the front flange on the cartool connectors.  The strap has a 5/8 hole drilled to be welded/filled to the underside of the trany cross member.
I used a tapered drill bit with steps of decreasing diameter to enlarge the holes beyond standard smaller drill bit diameters.
The OEM frame of the car has 5 holes 5/8-3/4 diameter drilled on the inboard vertical face to weld the aft end of the new box tube to the OEM frame.  The outboard  side has 2 holes 3/8 diameter drilled thru the OEM flange and frame where the front leaf spriing support diagonal gussets are spot welded to the frame.  The new box tubing, the spacer, and the OEM frame and gusset are all welded together.  I was trying to tie the new box tube to each side of the OEM frame the best I could.
I bolted the outboard (vertical) spacer in place, then removed one bolt at a time and gave the spacer a "heavy tack weld" at each drill hole, that way the spacer was tight against the inside of the frame rail.  I then filed down the tack welds so I could reach down the holes with the welder to join the box tubing to the other parts.
I chose to make a single cut thru the floor, then bend the sides up to form flanges that will have holes drilled and filled as spot welds.  I also welded the loose edges of the floor to the box tubing to clean things up for painting.
I"ll have completion photos in a few days.

[go-fish]

That's good stuff Phil. I'll be copying this. Thanks for the pics and instruction.

[71chally416]

That's the right way to do it. Cut the floor and weld them to the floor.   

[femtnmax]

Here's some starting pics, and the front end of the box tubing welded to trany cross member.

[MoparCar]

They look great. I'm going to do basically the same with rectangular stock also. Nice job. Thanks for posting.

Wes

[whplash1]

This looks like the best way to tie the frames together.  However, I have to put new floors throughout and will have an issue cutting into $800 worth of new floor!!  How well do the ones that follow the contour work?  Is there clearance issues to the ground?  Not as strong?

[71chally416]

Well for one thing the countoured ones use the thin floor metal as a side of the "Box". For another they neck down to almost nothing on one side. IMO they are more for looks than function.

[femtnmax]

Here's a few more photos of floor attached to box tubing.  Spot welded the upturned floor flanges to the tubing, then welded all the loose seams.  Maybe a little extra welding over a straight seam, but I wanted to give the floor as much self support as possible with the welds in shear rather than bending.
For welders like me who don't do it for a living, the web site "autobody101", in the "how to articles"  has an article on "basics of mig welding" that helped refresh my learning curve.  One thing they emphasized was to have a tight fit between parts prior to welding.  This really helped the weld puddle flow smoothly.   When installing the box tubing I had scraps of 5/8 plywood jambed between the shop floor and what ever piece needed to be pushed tight for the next weld.
I attached the rear torque boxes after putting in a fair amount of time making them fit.  The rear seam goes over/under the factory leaf spring support, rather than entirely over.  Had to cut one bend completely loose to get the D3%&*!! thing to match up like the OEM ones I copied photos of (from this web site).   I added spot welds at the forward edge where the torque box meets the floor skin, then also welded the free edge of the torque box.  Just a little extra stiffening.  Theres a photo showing the spot weld holes in the floor ready to be filled.
I selected these torque box pieces because they have the upturned flange all the way around the square access opening for the leaf spring hanger bolts.  This flange stiffens the cutout in the torque box so the compressive load from the spring hanger is transmitted thru the torque box to the unibody, just like the factory did it.  Without this flange the torque box would buckle at the opening and not distribute the load.   So I guess I'm saying I would not buy rear torque boxes that don't have the stiffening flange around the cutout.  JMO.  I also placed plenty of welds on 3 of the 4 edges of the torque box just like the factory.  The fourth flange evidently doesn't need welded because there is a major bend in the torque box to stiffen that edge.  Without enough weld length the torque box skin would want to buckle.  Like shear panels in house framing - need to firmly fasten all the edges.
Parking brake won't go in for awhile, but looks like maybe relocate the pedal cable inboard of the frame connector, and shorted the cable that links to the two axle cables.
This whole frame connector thing is just what I came up with.  Not saying its the best way, but it seems plenty solid.

[elitecustombody]

that looks great,one question, how well will the carpet and seats will fit and work?

[boydsdodge]

I have done it this way on a few a bodies but not an e body yet.
I used the same torque boxes as you did and I loved them, the way they fit on the back was near perfect for me, the fronts had to have upper inside corner trimmed to get it to roll up in to the floor frame intersection.

[BIGSHCLUNK]

that looks great,one question, how well will the carpet and seats will fit and work?

Wondered that myself. 

[femtnmax]

that looks great,one question, how well will the carpet and seats will fit and work?

The front seat bolt holes show up in the photo of the finished connector reaching up thru the floor.  Note the connector is dropping out of view, and the bolt holes are on raised pads, so front seat fit should be perfect.  Rear seat attaches to clamp brackets that are behind and above the connector where they pass out of passenger compartment.
I'm replacing the carpet, so I'll use pieces of the old carpet formed into inverted "U" shape and hand sew them to in place after cutting slits in the new carpet.  Sort of like repairing the sail on a sail boat.  Large diameter needle, maybe curved needle, and pliers to push-pull the needle thru.  I'll go to the boot repair shop to find some real tough polyester thread, or what they recommend.
I'll put a front seat in place, and take a pic, post tonite.

[go-fish]

I was thinking what I would do and I was thinking some foan to make it all even and aid in sond deadening.

[femtnmax]

I have done it this way on a few a bodies but not an e body yet.
I used the same torque boxes as you did and I loved them, the way they fit on the back was near perfect for me, the fronts had to have upper inside corner trimmed to get it to roll up in to the floor frame intersection.

I picked up the initial idea of the connectors from the "Big Block Dart" website, then went from there.  Thanks big block dart
Here's some photos of the seat clearance.  Seat is all the way rearward, and there's plenty of room.
I like the foam idea.  Have to look into that.   Thanks.  Maybe glue a thin sheet of plywood on top of the foam to give it some stiffness, then you could stand on it.  Just a thought.

[72bluNblu]

Have you routed the brake line, parking brake cable, and fuel line yet? Looks like the front section of the frame connector covers the holes in the frame for the brake line and fuel line...