Mmf
Ech
Tech | IRS Install
Factory Five Racing IRS conversion for the Comet Wagon
Independent
Thinking
By Jefferson Bryant
L
ive axles are great for drag racing.
The suspension is easy to tune,
the parts are strong, plentiful,
and inexpensive; for straight-line
racing, the live axle is hard to beat.
Put the same rearend in an uphill righthand
hairpin, however, and your suspension is
going to cringe, which can leave you in the
gravel. For road racing, there is nothing better
than an IRS or independent rear suspension.
Giving the drive wheels the ability to articulate to a changing road surface independent
of either side gives you an advantage over
the traditional live axle. The problem comes
in converting a straight axle car to IRS.
Part of what changed the Mustang from
a “secretary” car into the most successful
performance platform in the world was its
success on both straight and twisty tracks.
Vintage road racing is full of early Mustangs,
making the aftermarket full of great race
parts. The proven performance of an IRS swap
can be found for the first pony cars, but they
definitely are on the pricey side, starting at
around $5,000 for a basic kit. For the budget
enthusiast who doesn’t want to drive a Miata,
that cost tends to push the IRS swap out of
reach. When we decided to add an IRS to this
’62 Mercury Comet Wagon project, we knew
this would be a challenge, especially trying
to make it happen on a budget of less than
$3,000.
The early Falcon/Comet platform is what
the Mustang was developed on, but there
are a few key dimensions that changed, specifically the width. The Mustang is 1.5 inches
wider than the ’60-’63 Falcon, so even the
aftermarket IRS won’t be an exact fit. After
about eight months of researching, we found
an answer—Factory Five Racing. FFR builds
some of the coolest reproduction kits on the
market, the MK-series being the Cobra roadster platform, currently in the fourth generation, the MKIV. When you order an MKIV, you
have the option of live axle or IRS. The FFR
IRS uses a few factory components from the
’89-’97 V-8 Thunderbird installed into FFR’s
tubular IRS cradle that is designed to match
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up to the MKIV chassis. The Thunderbird IRS
is often used for IRS swaps for trucks, but
the issue with using it as-is in the Comet
is the width. The track width on the Comet
is a scant 54.5 inches, where the T-bird is
rocking 60.2, which would put the hubs past
the edge of the rear quarter-panel. The Factory Five IRS cradle also uses the 60.2-inch
width, unless you opt for the pin-drive setup,
which is designed for using knock-off adapters. This narrows the overall track width to
54.25 inches, and that we can deal with.
The installation required
some planning, and this is
not a bolt-in by any means
everything from binding up at full articulation.
We ordered the pin-drive kit, which comes
with new axle-shafts, tubular upper and lower
control arms, parking brake cables, and all
of the bolts. We also ordered a set of Koni
coilover shocks from Factory Five.
The installation required some planning,
and this is not a bolt-in by any means. The
cradle is a close fit to the Comet’s subframe,
but not close enough, so each mount was
fabricated under the car. We did not need
a tubing bender; all of the mounts are
made from thick-wall square tubing that we
sourced at the local metal supply shop. As
with any fabrication project, cut once, measure, cuss like a sailor, and then cut it again
(or something like that—Ed.).
There were a few unexpected issues we
found during the install. One in particular is
the upper-control-arm-to-subframe clearance; there isn’t any. With the upper arm
installed, it comes into contact with the
subframe before ride height. To fix this, we
simply notched the subframe using a piece
of 4x5 square tubing. Another issue turned
out to be the factory tolerances. The 1960s
3
Once we had the basic plan, we called the
guys at FFR and discussed it with them. While
they thought we were off our rockers, they provided us with the necessary dimensions that
we would need to ensure the system maintained the proper geometry. The upper mount
is separate from the lower cradle; it has to be
installed a specific distance from the lower
cradle, centered above it, and at a specific
distance to the front of the cradle. This keeps
1
The Factory Five cradle comes with most of what you need, including the bolts to put it together.
4
The entire process was done on a four-post lift
to make access easier, but it could be done on
the ground just the same.
2
The parts that the kit does include
are the donor parts from the ’87-’97
Thunderbird (V-8 8.8 only). We scored
an entire car (’96 model) for less than
$500, yanked the 4.6 and scrapped
the rest. In the end, we broke even and
got the parts we needed. The spindles,
center section, brakes, and the
associated hardware are all that is
needed. The rest can be scrapped
for lunch money.
5
The first step was to mark the centerline location
of the stock rear. We used a carpenter’s square,
a level, and a measuring tape to mark out the
exact vertical and horizontal centerlines, as well
as took some measurements and noted those
on the tape. We used masking tape on the body
so we could read the measurements and this
also ensures that we don’t lose them. Next, we
removed the entire stock rear suspension.
6
We had the factory parts blasted locally
and then disassembled them. To keep the
parts looking good, we sprayed them with
Eastwood’s Rust Encapuslator and followed
that up with some of the company’s Extreme
Chassis black.
The Koni
shocks require
assembly,
which is
simple
enough. You
do need to
pay attention
to the
direction of
the threaded
sleeve; it can
be installed
upside down.
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Mmf
Ech
Tech | IRS Install
7
The Factory Five tubular control arms
come in a nice gloss powdercoat.
Sometimes the internal threads
get some coating too. We used our
ratcheting tap and die set from
GearWrench to clean them out.
8
Before doing anything on the Comet, the entire assembly was pre-assembled on the bench.
9
Using the precise measurements from
Factory Five, the upper control arm
crossmember was positioned over the
main cradle and tack welded to the
temporary support beams (white slotted
bar in the upper right).
10
Then, the cradle components were
positioned under the Comet. We used
an assortment of beams and shims to
the get the cradle centered correctly.
During this time, the hubs and new
rotors were sent to the machine shop to
be drilled for the correct 5- on 4.5-inch
bolt pattern, and new bearings were
pressed in.
MDMP-130800-IRS.indd 44
11
The wheel centerlines on the body were used
to transfer the centerline to the subframe
for better reference. Then we made some
measurements under the car to make sure
it was square. Use multiple points to ensure
accuracy.
12
At this point, the upper control arm was
bolted in to check the alignment. It was here
that we discovered a big problem. The arm
hit the subframe before it would be at ride
height.
5/28/13 3:35 PM
manufacturing processes were notorious for poor tolerances, and there
were several areas that were not the
same side to side on the wagon. In
order to keep it tracking straight, we
needed verifiable reference points
on each side. In the end, we measured from several points on the car.
Depending on what vehicle the
donor parts come from, you could
end up with an open differential. We
didn’t know the specs of the 8.8 that
we had, so we chose to rebuild it with
parts from Randy’s Ring and Pinion,
adding a Yukon Sure-Grip LSD and
a set of 3.73 gears. Those parts are
not included in the project total,
though, as they are not required for
every swap.
Aside from the basic handtools, you will need a MIG welder,
chop saw, reciprocating saw, and
a plasma torch if you can get one.
The plasma torch is really nice when
working with some of the tight spots
and thick metal, but you can do it
without one. A lift is really helpful as
well. We put the Comet on our Quality Lifts 4-post lift and the added
headroom under the car made this
project much easier than lying on
the ground and dropping hot slag on
your stomach.
One other note—with the cradle
installed, fitting the center section is
a tough task. There is a sweet spot
on the passenger rear section of the
cradle where the pumpkin can be
rolled into the cradle. Keep that in
mind for your swap. The 8.8 weighs
about 80 pounds, so it takes four
hands to move it around in this tight
spot.
For the running gear, we picked
up a set of Weld Racing S71 18s
and 20s, wrapped in BF Goodrich
G-Force Radial TA KDW rubber. The
lightweight forged wheels look ridiculously good against the Comet body
and the large open spokes provide
ample cooling area for the brakes.
This swap will work on any early
Mustang or Falcon platform, and the
total price is less than any custom-fit
IRS kit, ringing the register at $2,600
for the cradle and T-bird IRS components, we replaced the hub bearings
and rotors for an additional $250,
bringing the total to $2,850, under
our $3,000 goal.
We spent about four days installing the cradle into the Comet, and
the results could not be more
impressive, on the ground, you can’t
tell the wagon has an IRS, and who
would even think it would?
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13
We marked the offending area on both the inside
and outside of the subframe. Using a Miller
Xtreme 380 plasma torch, the subframe was cut
out. We used a reciprocating saw for the vertical
sections.
14
The subframe was boxed in using a section of
rectangular tubing to regain the loss in strength.
This will be sturdier than the original.
15
The upper crossmember is not wide enough to
span the width of the subframe, so we made a
pair of adapters. These are made from 2x 1⁄4-inch
strap and 3⁄16 -inch-wall 11⁄2 -inch square tubing.
16
These adapters increase the width of the
upper crossmember and match the angle of
the subframe. We bolted them to the upper
crossmember and welded them in place.
17
Next, the upper crossmember was
repositioned under the car and the subframe
was drilled to match the holes in the upper
crossmember.
18
Then we bolted the upper crossmember to
the subframe. It will be welded in after the
rest of the cradle is tacked in place.
19
The lower cradle is designed to match up
to the MKIV chassis, but the Comet does
not need the extra material. We marked the
excess material on the front lower portion of
the cradle.
21
The lower cradle was repositioned under
the car and the rear upper crossbars were
welded to the bottom of the subframe. We
cut a triangle gusset and added that to the
end of the upper mount. This is similar to the
MKIV process.
One other note—with the
cradle installed, fitting
the center section is a
tough task. There is a
sweet spot on the
passenger rear section
of the cradle where the
pumpkin can be rolled
into the cradle.
22
The front frame supports were made from
¼-inch 2x2 square tubing, running at a
45-degree angle from the cradle to the
corner where the subframe meets the floor in
front of the stock shock mounts.
20
We then cut it
off using the
plasma torch.
We made some
endcaps and
welded them to
the ends to box
it in. This also
provided a nice
base for welding
the forward
cradle-to-frame
supports.
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Mmf
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Tech | IRS Install
23
The Ford 8.8 center section was in good
shape, but it had been sitting around with
the bearings exposed to dirt in the shop for
about six months, so we rebuilt it. Equipped
with new 3.73 gears and a new limited-slip
carrier from Randy’s Ring and Pinion, the
8.8 shouldn’t have any problem transferring
power from the 347ci stroker engine and TCI
6X transmission to the ground.
24
The control arms have both adjustable
rod ends and shims. This allows for the
more adjustability in the caster, camber,
and toe. We stacked the shims equally
on both sides for the baseline.
26
25
The shocks proved difficult to bolt down.
Both the nut and the bolt have limited
access, so you have to use an open-end
wrench. The aluminum spacers are specific
to the front/rear placement, otherwise the
body will hit the control arm.
The axles are next. These are also new
with the kit, since this is the narrowed
pin-drive setup. The non-pin-drive
reuses the stock axles. The spindles
(also referred to as knuckles) bolt to
the control arms using the original
hardware.
27
We slipped the rotors and brakes onto the
spindles and everything fits. This is about as
cool as it gets.
28
The last step was bolting on the new 18s and 20s from Weld Racing with 30-series BFG tires.
We were concerned about everything fitting, but we measured correctly and had no fitment
issues. There is even room for proper caster/camber adjustments. These forged wheels are
deceptively lightweight; the tires weigh more than the wheels.
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29
We filled the center section with Royal
Purple Max-Gear gear oil. There is
actually plenty of room to pour straight
from the bottle, surprisingly.
We spent about four
days installing the
cradle into the Comet,
and the results
could not be more
impressive, on the
ground, you can’t tell
the wagon has an IRS
Sources
BF Goodrich
(877) 788-8899
www.bfgoodrichtires.com
Eastwood Company
(800) 343-9353
www.eastwood.com
Factory Five
Racing, Inc.
(508) 291-3443
www.factoryfive.com
GearWrench
(800) 688-8949
www.gearwrench.com
Miller Electric
Manufacturing Co.
(920) 734-9821
www.millerwelds.com
Randy’s Ring & Pinion
(800) 292-1031
www.ringpinion.com
Royal Purple, Inc.
(888) 382-6300
www.royalpurple.com
Weld Racing
(800) 788-9353
www.weldracing.com
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