bend a weld technique:
Steel, a pattern, and fabrication tools. Everything needed to
build side rails
Some years back I built my own weld in sub-frame
I wanted something that contoured the underside of my Mustang and
connected the front frame rails to the rear frame rails. This
required a square tube that had bends going on two different
axis. A tube bender would have worked well to make this part but
I do not have one and as you know I am all about keeping it DIY so I
came up with a technique I call "notch bend and weld." It allowed
me to easily make the bends in the tubing without compromising
strength. I mention all this because I used the same technique to
make the side rails for my IRS install.
The concept is really simple. You start by cutting a wedge shape
out of the square tubing. The angle of each half of the wedge
be 1/2 the total angle needed at the bend. A real world example
of this would be a picture frame. At the corner you want
90º. To archive this, each piece of the the frame material is cut
45º angle with the two cuts being opposite of each other. Exact
same concept applies to notching the tubing to build the side
rails. On my side rails he two sharpest
angles are 55º so in theory each side of the wedge would need to be
27.5º. The reality is I wanted a little bit of a gap to fill with
weld and I also wanted some adjustment prior to welding so that I could
get everything exactly where it needed to be. With this in mind I made
my cuts at 30º per side to make the
When cutting out the wedge there are a couple things you need to do to
insure a good bend. First you need to use a square and mark a
line, through the middle of the desired bend, all the way around the
tube. This line gives you a reference to insure the wedge is
uniform in shape.
The second thing you need to do is cut into the outside edges of the
bottom side of the tubing. (the side that will be bent when you close
the gap) The way square tubing is made there is a radius on each
corner. If you do not cut through that radius it will be harder
bend and when you do get it bent the corners will pucker out and not be
uniform. If you look
at both pictures below you can see the cuts I am talking about.
I first started building these side rails I used a plasma cutter to
cut out the wedge and then a cutoff wheel to cut through the corners on
the bottom side, but after a few notches I realized the cutoff wheel
gave me a cleaner cut with better control so I used it by it self to do
remaining cuts. Once I had my notches cut and cleaned up I bent
side rails so that the first joint was at the angle I needed and tacked
welded it together, I then moved on to the second and third
joint repeating the process.
I used my pattern as well as angle finding tools to build the first
rail. After I had it together I test fit it in the car and made
sure it fit as well as the pattern had, which it did. To make the
second frame rail
I repeated all the steps from the first rail but instead of using
my pattern and angle finding tools to get the correct angles at the
bends, I used the first frame rail to line up the second frame rail so
they were an
identically matched pair.
The final result is a set of side rails that do exactly what they
were designed to do, they bolt into the OEM leaf spring mounts and
provide something to anchor the rest of the IRS sub-frame and
to. There are many ways a person can do a Jaguar install in a
classic Mustang but it's these side rails that allow it to be a true
in. The rails look simple enough but I had almost 8 hours into
them. At the point of this picture the rails were
currently only tack welded together, I still needed to weld them up
including fish plates, but that was intentionally put on hold until the
the project was further along and I knew that no other changes needed
made to the rails.
I have documented this project both on this web page as well as on www.IRSuspension.com
forum and there
are at least three Mustangs out
there with a Jaguar IRS under the rear, and while many things on the
IRS install on these other cars were done differently than the way I
did mine, every install uses my side rail concept.
If you have not figured it out yet the primary function of DazeCars
is to share information and help others build or modify their classic
car, especially if they want to make your classic ride "better".
So when I was contacted through the forum,
by the fabricator who would eventually install three IRS units in
Mustangs, asking for specific information to begin his own
IRS install, I was more than happy to help.
I am ready to build the
side supports and just thought of asking for the plans. My car
is on the ground and drivable so preparing everything and then making
it a one day job is what I prefer... Can you give me the
measurements for the side supports?"
drawing is not to scale, but should give you a general
idea of what I have going on. Let me know if I can help further."
Rear Shackle Mount:
it came to the rear shackle mounts I had several ideas, some of which
were better than others. Just like the custom mounts I made for
the front, my rear rubber mounts are typical 9/16" hole Mustang shackle
add rigidity and get the ID to 1/2" I press a 5/8 sleeve in to the
bushings. The internal steel sleeve goes in fairly well but does
pressure and had me wondering what the best idea for the rear mount was.
I could use the stock upper hole in the
frame, install the shackle
bushings as designed and then run a solid steel piece that is welded to
side rails and connects to the OEM mount. This idea is the most
but I am worried that I will not be able to get the 3" sleeve pressed
to the two bushings to tie them together, do to the limited room to work where the bushings
located in the car.
second idea was to set it up the same as above but use poly bushings
which are way more rigid and already have the 1/2" ID hole. The problem
with this is I don't like poly, it doesn't flex enough IMHO and I am
that there will be more flex in the front than the rear because the
front bushings are rubber.
option is to use a shackle design utilizing the poly bushings in
the Mustang frame and then weld a sleeve to the end of side bracket
like the one in the front to house the rubber bushings in the lower
shackle location. If I did this I should have fairly even flex, front
to rear, but now I am using two sets of bushings and even more
fabrication will be required.
posted these ides on the forum and got lots of replies. The IRS
forum is a fantastic place for brain storming and I used the
collection of minds there often when problems came up so that I could
achieve the best possible solution. Ultimately I came up with a
design that has both the ease of install and the similar mounting
flexibility to the front bushing.
I realized I was making
it way to
complicated. The fix was to use one set of rubber bushings in the
as originally designed, and hard mount the lower part of the "shackle"
my side rails. Inside the Mustang frame rail I use two rubber
bushing with a 1.5"
sleeve instead in each one instead of of one 3"
sleeve runing through both bushings, that way I can press each steel bushings into a rubber
bushings, and then install the bushing/sleeve combo independent of each
second issue with the shackels was I had originally intended to use two pieces of 1/4"
flat stock like shackles and weld both of them solidly to the side
rail then run a bolt through the bushing/sleeve combo at the frame.
Problem was the space between the upper
frame mount and the gas tank or the frame and the rear quarter panel is
not large enough to fit a bolt long enough to go through the bushings
and "shackle" pieces. Normally when installing new shackles you put the
bolt through the flat bar and then slide one bushing over the bolt,
from there the inner bushing is inserted in the frame and the opening
for the bushing in the frame is big enough that you can angle the bolt,
flat-bar, bushing assembly into place. I would not be able to do this
if flat bar pieces are welded to my side rails. The solution to this issue was to drill a hole through the flat bar and
my side rails, and bolt both the frame mount and the side bar mounts
in place instead of welding them to the side
rail. Basically I am using the OEM shackle concept to mount the rear of my IRS sub-frame.
Above we have the final rear mount design. The spacers will be
welded to the side support and then the inner
shackle plate will be welded to the spacer. A 1/2" bolt will then
through the welded plate, through the spacer, through the side bracket
through another spacer and then pass through the removable shackle
love to know the actual tolerances Ford used when they built the
Mustang 45 years ago:
At this point my side rails were welded up solid and mounted in the
two side rails were identical to within a 1/32", but when I bolted them
in the car I discovered that the original frame rail mounts were not
identical. On the drivers side (side I took the measurements from) the
shackle plates are at a perfect 90º in relation to the back half of the
side rail, but on the passengers side the same shackle brackets are
a couple of degrees off of 90º. I don't really think this is an issue
other than the fact that it really bothers me. Also the
passengers side, side rail sits
about 3/32" closer to the Mustang frame rail at the top of the frame
The good news is that the side rails are still level at the top
section front to back on both sides, and the side rails are still
level in relation to each other, and since the car is currently level,
I know that I can proceed in spite of the differences, but the side of
me that strives for perfection sure wishes the car was a little more
viewing pleasure, my mocked up support system:
I got the support system
roughed in. The crossbars are not yet welded in (or correctly
in the picture). When this picture was taken,
the hardest part was calculating
the differential location.
I was mounting the top of the
differential flush against the crossbars
so the pinion tilts 5º up to match the transmission's down angle. Angling
the pinion up shafts and wishbones forward so I had to
calculate how much so that the differential can be moved back far
enough to center the tire in the wheel well at ride height. Also I had
to figured out the
off set between the cross bars and differential so that the upper shock
mounts would bolt to the cross bars. I measured many times before I was
able to mock things up.
With the side rails installed and the crossbars coming together I was a
lot closer to mocking up the rear end. In page VII I will address the
brakes including their rebuild and address the fabrication required on
crossbar to make them fit.