As you can see, we got a little carried away on this one. Follow the links above to see what was done with each chassis system.

Chassis Jig Design and Fabrication

All the talk about custom suspension sounds great on paper, until you actually think about what it involves.  Clearly all of the parts from a 2004 Mustang were not designed to bolt up to 1968 Torino.  This leads to several questions.  On of the most frequently asked questions we get is how do you know where to put everything?  How can you ensure everything is set up the same from left to right, front to back and vertically?  How can you build a second car faster (in our case).  It would also be helpful if it could somehow be referenced to known published data from a Mustang.  The problem is, if you located one critical component incorrectly, everything else that goes on after that will be off, and will be very difficult to fix.  A small amount of time invested here will be well worth the effort.

Enter the chassis jig.  If a garage floor was perfectly flat - this would be a great measurement reference.  Unfortunately, most are not flat as they are sloped for drainage.  Besides that, a floor is definitely not portable.  The other problem is that is difficult to bolt, clamp or weld fixtures to the floor.  There is also little to no repeatability if you switch locations of the build, plus it is easier to work on the vehicle when you can access it from below. 

Rather than spend thousands of dollars to buy a commercially available unit, we decided to do some research and build our own.  As you can see below, first a concept was drawn up in Solidworks to get an idea of what it would and should look like.  After going through a dozen ideas and revisions, the following is the final design.  The objective of this is to build a portable chassis fixture that is perfectly flat (easier said than done as we found out) and could be leveled on any floor surface using adjustable feet.  The structure needs to be simple enough that it is easy to work around, but at the same time has enough bracing that it is stiff enough to resist deflection once a complete vehicle is set on it.  This may not be the most practical thing to do for someone who is only going to build one car, but for us, there will be many cars built over time.

The next part of the process involved getting materials etc.  The main structure is built out of 3"x3"x1/4" steel, and the cross bracing is made from 2"x2"x3/16" steel.  The adjustable feet were purchased at a local industrial supply store.  The legs are made by Carr-Lane and are part number CL-8-SLF.  Turns out we found the steel through a wanted ad we placed locally on Craigslist.  The steel was from a local billboard that was torn down and being sold for scrap.  The price was right, so we drove away with a truck loaded with steel (the truck seemed to sag nicely after this).  The steel was not the nicest looking as it was covered in rust, but that is nothing a little paint can't fix as you can see.  The following is a cost breakdown for the basic shell of the chassis jig:

~100ft 3"x3"x1/4" steel: $100 (Leftover steel will likely be sold to recover some cost)
2"x2"x3/16" steel: Found in scrap bin
Leveling feet for base of legs & nuts for legs: $70
Paint and misc shop supplies: $35
Total cost: $205
Labor: No charge :)

Fortunately, we had access to a commercial surface plate as a starting point to ensure flatness of the top surface.  A straightedge was also used to ensure the part was flat during the process.

As you can see below, the jig is not very complicated, and is basically made up of simple rectangular beams cut at 90° or at an angle in the case of the braces.  We opted to MIG these parts together as it is a lot faster and puts less heat into the parts (with the exception of the base of the legs where TIG was used).

Seems simple enough.. however once you weld these pieces together, there is a considerable amount of movement of the pieces (considerable being measured in mm), and once the jig was unclamped from the surface, the residual stresses in the parts caused some of the ends to lift.  Since this meant the top surface is no longer flat, this is a big issue.  Time spent here to make the jig as flat as possible is well worth it.  This proved to be the most tedious part of the build, where we had to cut some of the welds, apply heat to joint, and then re-weld.  This was done over and over again until the jig was perfectly flat on its own using 12' straightedges.  Once finished, the jig was coasted in Miller Blue of course :).

Chassis Jig Add-ons:

Body Cradles

The first and most obvious addition to the chassis jig are the body cradles.  The allow the body to be clamped to the chassis jig, and also allow the body to be raised and lowered relative to the top face of the plate.  The reason for this becomes more obvious after looking at the suspension cradles.  There are two similar body cradles, one front, and one rear.  Each cradle has two screw jacks which allow the vehicle to be positioned precisely up and down.  These were made using 3/4" threaded rod and nuts from Home Depot.  The rest of the cradles are made of 2x2x1/8 steel which was welded together using a TIG welder (just cause).  One of the nuts is welded to the base, one to the adjuster rod, and a third is used as a jam nut.  With this design, the car can be raised and lowered from below with an impact wrench.  We decided to use a plate that will be welded to the torque boxes of the car and will act similar to a dowel pin for locating the vehicle, which can be seen below. 

Plywood Measurement Surface

As noted below, one of the goals in building the chassis jig is to make it perfectly flat, both in construction, and when it is set up underneath the vehicle (using the adjusters).  This is done so you can now put gravity to use.  The inside portions of the jig were made to be 48"x48" so a std plywood sheet could be put in between (aside from it being ideal outer dimensions to boot).  The sheet of plywood can now be used to mark on for measurements, centerlines, etc.  A simple plumb bob is used to determine locations both laterally (cross car) and longitudinally (lengthwise).  The heights can now be determined using height gauges and steel rules using the flat base across the jig as reference.

Suspension Cradles

When you first start a project like this, you don't really know where the suspension needs to go at first.  You have a rough idea of where the body needs to go, but that is it.  Before the actual mounting components can  be fabricated, the suspension and body will be mounted independently to the chassis jig.  There is one cradle for the front suspension/engine, and another for the rear IRS.

Both the front and rear suspension will be placed at "as designed position" which provides for optimal suspension dynamics.  Unlike a lowered SN95 Mustang which causes the vehicle to ride up the camber/toe curves, our vehicles will be lowered, but behave as though there were designed in that position.  We will not have to worry about things like bump steer as a "modified lowered" Mustang would.  This may mean we will have to cut holes in the trunk floor to clear the IRS, but it is worth it for the performance advantages.

Front Suspension/Engine Cradle

In order to get the suspension in place and get it to the right height, we needed to build a fixture that would work with our chassis jig. The k-member was used as reference and mounting points were chosen and located. Once this was built, it was placed on the vehicle so a tire and wheel could now be put into place.

Rear IRS Cradle

The cradle for the IRS is shown below.  This piece clamps to the chassis jig, and allows for height adjustment/pitch of the IRS assembly.  The cradle picks up on 4 existing holes in the IRS, which will make this a valuable tool for any IRS installation from now on.  Thankfully we had and extra IRS cradle and control arms for the build to make the parts easier to work with.  The design was first made up using Solidworks to figure out the lengths etc, then was physically built as shown.  The fixture also allows the height of the control arm to be adjusted to set the wheels at the correct ride height.

Solidworks conceptual CAD design with and without chassis jig in place

Fabrication of actual fixture using mocked up decontented IRS

     
Final completed fixture (missing control arm height adjusters)