A quality set of connectors, that fit like they were Ford designed original equipment, can be fabricated with basic tools skills and a very little money.

Plans for  building connectors for a 64.5-73 coupe or fastback.  The bottom drawing is the side view and the top drawings are the top view of both connectors D-side and P-side respectievly.

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The Mustang is a sports car?
  -  The Mustang has the heart of a lion with the sleek sporty lines to rival any sports car, but it is built on the chassis of a 4-door family car, the Ford Falcon.  In other words, when it comes to chassis performance, specifically in handling, the Mustang has LOTS of room for improvement.  One attribute of the Mustang that it definitely gets from it roots in the Falcon, is the unibody design. Basically, unibody means that the car does not have a solid frame running full length of the car from the front to rear.  The lack of a frame is accomplished by short frame rails at the front to attach the motor to and frame rails at the rear to attach the rear end to.  Connecting these two sets of frame stubs is nothing more than the body of the car, more specifically the cab. Ford and many other manufacturers used this design because it was cheaper to build and lighter.  The problem with this design is that the body must hold its own weight and react to ever changing road conditions.  Off of the factory floor, the unibody design of the Mustang worked well, but over the last forty years, daily abuse coupled with rust in key locations, can cause a car to sag in the middle.  Even if the car does not sag, if you look at any unrestored early Mustang, you will find a crack at the rear base just below the rear side windows on one or both sides.  This is the result of flex in the unibody. One simple fix to improve the overall structural integrity of a Mustang, and a must for any Mustang that is going to be used in performance applications, is to install sub-frame connectors that join the front and rear frame rails, making the frame a solid unit that runs the full length of the car.

Other Tech Articles
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www.dazecars.com
- Putting Independant Rear Susprnsion or IRS in a classic Mustang 
Page I : Why make the upgrade and Fords original IRS design
Page II : Where to find a unit, taredown, and cleaning.
Page III, Narrowing of the LCAs and half shafts and converting the Jaguar bolt pattern to a Ford bolt pattern.
- Retro fitting modern seats in a classic Mustang
- True ram air ( Thunderbolt style )
- Increasing horsepower   "Efficiency -vs- Volume Increases"
- performing the UCA drop AKA Shelby Drop, or Arning drop on a classic Mustang, Cougar, or Falcon
- Improve Mustang suspension by building a set of  Roller Spring Perches
- Fabrication instructions for building a set of  homemade adjustable strut rods.
- Putting a modern Mustang E-brake handle in a classic Mustang.
- Understanding Bump-Steer and eliminating it or reducing it effects.
- Building a bolt-in spring compressor or ball joint tool.
- Suspension 101 Understanding the basic concepts of Mustang Suspension including most of the aftermarket kits and options.
- Fabrication process for building a 9" rear end for a 1964.5-1966 Mustang

Roller spring perches

T5 Hydraulic Clutch Brackets

DIY Roller Spring Perch Master kits

Steel UCA Drop Templates

17/32" Drill Bits for UCA Drop

CSRP Disc brake kits


  -  Sub-frame connectors are such a popular upgrade that there is a host of options in the aftermarket, from generic pieces of steel with no bends, tubular units, and other options designed to contour the underside of the car and more aesthetically mimic a solid square tube frame.  Although the aftermarket offers both weld-in and bolt-in sub-frame connectors, the walls of the front and rear stub frames on the Mustang are so thin that bolt-in options are ineffective.  NOTE:  in my humble opinion ALL, sub-frame connectors, even the bolt-in kind, need to be welded into place.  A person can spend quite a bit of money on sub-frame connectors, but for less money a quality set of connectors that fit like they were Ford designed original equipment can be fabricated with $25.00 in steel, basic skills, simple cutting tools, a welder and the following information.  NOTE:  the following info is for building connectors for a 64.5-73 coupe or fastback and does not directly apply to convertibles, due to torque boxes under the car.
  -  Before you start this project you need to evaluate your welding skills.  The following is the process for constructing an intrical part of the Mustang support frame and if your welding skills are not sufficient for the task, catastrophic failure could occur.  NOTE: If you have any doubts AT ALL about your welding skills, DO NOT ATTEMPT TO MAKE YOUR OWN SUB-FRAME CONNECTORS!!  One option for the non-welder is to prep the materials and then take them to a certified welder for assembly and instelation.

Tools required:
Cutting tool
Angle grinder
Welder
Angle finder
Tape measure
Materials required:
2” x 1/8” plate steel, about 4 feet
2” square tubing 1/8” walls 8’

Fabrication Process:
  -  The first step is to cut two 4’ pieces of the 2” square tubing. Once the pieces are cut, they need to be marked at the points where the connectors need to be bent.  I made the marks on all four sides of the tubing at all four bend locations.  The first measurement is 6.5” from the front, the second measurement is 12.75” from the front, the third measurement is 25.75” from the front and the fourth measurement is 35.75” from the front, which should leave 12.25” from the last measurement to the end of the tubing.  Each one of these measurements is going to be a bend in the tubing.  Once you have the original measurement marks, additional marks need to be made so that notches can be cut out of the tubing. When the notches have been put in and the tubing has been bent, the final result of the bending needs to be that the first and third bends are 174 degrees and the second and fourth bends are 170 degrees.  The first bend needs to be down, the second bend needs to be towards the outside of the car, the third bend needs to be up and the last bend is towards the inside of the car.   To best achieve proper angles and consistency, two things need to happen.  The first thing is that the correct wedges of material need to be cut from the tubing and the second is that a jig needs to be made to ensure uniform angles, which will be discussed later.  
  -  When it comes to the proper wedge thickness being removed, the 174 degree bends need to have a 1⁄4” of material removed from the inside of the bend, and in the same way the 170 degree bends need to have 3/8” of material removed from the inside of the bend.  To achieve this I split the distances, either 1⁄4” or 3/8” depending on the bend I was working on, putting lines on either side of the four bend marks I had already made.  I then drew angled lines from the edge of the lines I had just made to the centerline on the outside of the bend.  NOTE:  on an individual connector, the first and third bends need to be opposite of each other, as do the second and fourth bends.  When comparing the drivers side and passengers side connectors, the first and third bends will be the same on both connectors, however the second and fourth bends need to be mirror opposites of each other.  It is the second and fourth bends that determine whether or not you are making a drivers or passengers side connector.  Once the wedges have been marked, the wedge needs to be cut out.  This can be done several different ways ranging from a chop saw set at an angle to a cut off wheel or reciprocating saw.  It is important that when cutting the wedge you DO NOT cut through the bottom side.  For best results cut down to the inside of the wall on the bottom side.  Once the wedge has been cut out, I recommend grinding an angle on the cut edges to insure proper weld penetration.  Also, grinding the edges makes it so that when the edges come together they form a trough, which allows the welds to not protrude very far past the surface of the steel and if one chooses to grind the welds smooth after the connectors have been finished, most of the weld bead will remain intact.  Before the connector has been bent and welded, I recommend cutting a 45-degree angle on the bottom side of the connector in the end to make a smoother transition to the rear frame rail. Once the steel has been prepped, it can be placed on two sawhorses, with the top of the wedge up and then pressed down to the correct angle, closing the wedge and then tack welded into place.
  -  When bending the steel, for best results, the sub-frame connectors MUST be identical in retrospect to the corresponding angle on a single connector, as well as the corresponding angles on the other connector.  In other words, for best results, the four 170 degree bends (two per connector) need to be identical, even if the bends are + or – a degree or two, you want all four bends to be exactly the same (same thing applies to the 174 degree angles).  The easiest way to achieve uniform angles is to build a jig out of a scrap piece of 2” high wood or steel that is firmly connected at the angle you want. That way the jig and the connector you are working on can be placed side by side on two saw horses and the connector you are bending can be bent to match the jig.  Obviously, two different jigs will need to be made since there are two different angles. To build said jig, place the steel tubing or wood in a chop saw, set the saw at 5 degrees off of 90 for the 170 degree jig and 3 degrees off of 90 for the 174 degree jig.  Then take one of the cut pieces and rotate it 180 degrees and then match its face to the face of the other cut piece so that they can be lined up to achieve the desired angle, and firmly attach the two pieces together via welding or glue, depending on the material you are using.  Once you have the jig, place the notched connector next to the jig and bend the connector, closing up the gap.  The connector needs to be bent to the point where both sides are parallel with the two parts of the jig, and then tack weld the corners. If there is a slight gap between the two sides, it is not a problem because the gap can be welded closed.  After tack welding the bend, double check again and make sure the jig and connector are the same and that the correct jig was used for the bend.  Once the bend has been deemed accurate, you can weld it closed.
  -  Once all four bends have been made, the only thing left to do is attach a cover plate on the back angled cut 2.5” long 1/8” thick and 2’ wide, two side attaching plates on the end 3” long 1/8” thick and 2” wide and two spacer plates on either side in the front 6” long 1/8” thick and 2” wide.  The end plate needs to be positioned over the angled cut end and welded up on all four sides so that water and road debris cannot get inside the connector.  The attaching plate closest to the front of the connector needs to be 5.5” from the last weld with 1” of material on the connector and the second attaching plate needs to be 1⁄2” from the first.  I use two plates rather than one large one to have more surface edge area to weld to.  The spacer plates are spot welded to the front in several locations. The connectors can now be painted leaving any metal that needs to be welded exposed. The connectors are now finished and can be installed using the following instructions.

Two pieces of 2" square tubing 4' long are used to make the connectors

2The V-notch has been scribed in to the tubing

Once the notch has been cut out the edges can be beveled for better weld penetration.

The connector needs to be placed next to the jig and bent.  Once the correct angle has been achieved the notch can be tack welded closed.

Front spacer plates welded to the sides

Rear mounting plates and end cap


Cap ends of the front frame rails have been removed

Installed P-side connector

Installation Instructions
Before you begin the installation process you need to make sure the ground or the surface or lift the car is sitting on is level and that the car’s full weight is on its wheels.  

1.    In each front frame rail, drill three 3/8” holes in a triangle pattern, approximately centered,  in an area between the end cap and a measurement 6” forward from said end cap.

2.    When properly installed the sub-frame connectors slide into the OEM front frame rails, this requires you to cut the caps off of the OEM rails.  It is important you cut them just big enough to slide the connector in and that you leave a small bit of the cap at the top to seal the gap between the sub-frame connector and the floor of the car.  For best results cut off less then you think will need to be removed for a snug fit, test fit, and repeat until you get a nice sold fit.

3.    Once you have the sub-frame connectors fitting snugly position them so that the two side mounting spacer plates are almost completely inside the front frame rail.  With the sub-frame connectors in place mark the front and rear frame-mounting locations on the car to indicate where the sub-frame connectors will be welded in.  Remove the sub-frame connectors then clean and prep the marked areas for welding.  You can then reinstall the sub-frame connectors and tack weld them in place.  Use only a few tack welds so you can make fitment adjustments with the goal of making the connectors mirror image of each other.

5.    With the sub-frame connectors tacked in place, rosette weld (plug weld) the three 3/8” holes on each OEM frame rail, weld up the edge where the front frame rail pocket meets the sub-frame connecter and fill any gaps between the sub-frame connectors and the front frame rails.

6.    Weld around the rear mounting tabs, and place a stitch weld between the non-bracketed side of the sub-frame connector where it meets the rear frame rail.  Failure to stitch weld in this location may cause you to punch through the OEM material.

7.  To further improve the connection between the unibody and the frail rails several sheet metal angle iron brackets can be place where the connecters meet the floor pans and welded in place.

8.  A coat of paint or undercoating is recommended to protect your freshly installed connectors.



 
Here we have it, a completed pair of sub-frame connectors ready for installation.

Disclaimer on Daze Tech Tips
      I am not an expert in this field. I have performed these modifications myself with very good results. I am passing along restoration and performance tips for the purpose of education.  If you are concerned about reliability or safety issues, I do not recommend that you or any other individual perform these changes or attempt to modify your cars from stock configuration except under your own volition.  I do not assume nor accept any liability for the use of this information or how it is applied!