"The project so far has been
fun but
relatively simple and unchallenging, however, that is all about to
change as we are now venturing into the heart of the IRS project,
narrowing of the half shafts, narrowing the LCAs, and changing the bolt
pattern on the wheel flanges."
Where
we have been and where we are going: In
“Mustang IRS” page
I, we looked at
the original Ford IRS design for the Mustang, the reasons for upgrading
to IRS in a classic Mustang, as well as the reasons to use a Jaguar
unit rather than some of the other options available in the IRS
market. In Mustang IRS page
II, we looked at the logistics of
finding a Jaguar IRS unit, the task of tearing it down into its basic
components and the labor-intensive job of cleaning it up. The
project so far has been fun but relatively simple and unchallenging,
however, that is all about to change as we are now venturing into the
heart of the IRS project, narrowing of the half shafts, narrowing the
LCAs, and changing the bolt pattern on the wheel flanges
Getting
the correct track width: As with most
aspects of this project,
there are several schools of thought on making an IRS unit fit in your
application. One option is to use the Jaguar unit as it was
designed and then run wheels with extreme back spacing. The idea is
that the width of the rear end plus the minimal offset of the wheels
will be similar in width to a standard rear end assembly with normal
backspacing and off set. In
theory, this is a good idea,
however,
by requiring wheels with extreme back spacing, your wheel choices are
greatly reduced. Also, the hub on an IRS unit takes up quite
a
bit of space and some wheels with extreme backspacing may end up
hitting the hub. Another thing to consider in the case of a
Mustang install, is that the nearly 4” difference in track
width,
between an early Mustang rear end and XJ Jaguar assembly, may not be
completely compensated for by large backspacing wheels, and
modifications to fenders may still be required to make the assembly
fit. For these reasons, I chose to narrow my Jaguar unit for
a
correct fit.
When
narrowing any
rear end, whether it
is a live axle or IRS, you need to consider what you have planned for
the car with special attention paid to wheel and tire widths.
Some wheel and tire combinations, such as modern Mustang rims, may
require a slightly wider rear end. The stock 65-66 Mustang rear end
measures 58” hub to hub, so a target width of that, plus or
minus an
inch, should be your goal depending on your plans and
application. NOTE normally you
measure a Ford live axle rear
end
housing minus the brakes from housing flange to housing flange, and
such a measurement on a 65-66 Mustang would be
52.25”. For this
project, I measured from the outside of the hub instead because there
is no other place to get a measurement that translates on the IRS
unit. The width of an XJ6 or XJ12
IRS unit is
61.75”, wheel
flange to wheel flange, so to maintain the 58” width of a
64.5-66
Mustang, 1.875” needs to be removed from each side.
In the case
of my application, I chose to remove 2.125” from each side
for a final
width of 57.5” hub to hub. I chose this for two
reasons, first, I
wanted a little extra clearance for my tires, and two, the half shafts
start at 16.125” u-joint center to u-joint center and having
them
shortened to an even 14” just seemed to make sense somehow. Narrowing
the half shafts:
On the Jaguar
IRS
system, the half
shafts serve triple duty. They provide the connection between
the
differential and the wheels to drive said wheels, they act as upper
control arms keeping the hubs vertical during suspension travel, and
their connection to the differential provides a means of adjusting
camber. With so many functions, these parts are very
important
and the utmost care needs to be taken in narrowing them. I am
a
competent fabricator, however, the greater part of what makes me
“competent” is knowing when the task that lies
before me is beyond my
skill set. Narrowing half shafts is one of those tasks that,
for
all but a select few with the correct skill set and access to the
correct equipment, should be farmed out to a driveline shop. NOTE if
a
half shaft were to fail while in use, the results could be
catastrophic, so weigh the potential consequences and think very
carefully before attempting to narrow the half shafts yourself. If the Jaguar half
shafts were like a
typical driveline made from a piece of mechanical tubing with a yoke
pressed in and welded to each end, then there would only be one option
for narrowing them. However, when Spicer originally designed
and
manufactured the half shafts for the Jaguar, they decided on solid
forged steel pieces, much like the axles on a live axle system. This
creates challenges in narrowing them, however, it also allows for more
than one option on how to do it. Even though, in most cases,
the
work will be done by someone else, you, as the consumer, have three
choices as to how you end up with the correct half shaft length:
“Bevel
and weld”, “Turn down, cut, press &
weld”, “Fabricate from
scratch”, and with the aid of your machinist a decision can
be made as
to which is the best option for your application and financial
resources.
Bevel
and weld:
Hot rod builders
have used this first
technique to narrow the half shafts of Jaguar IRS units for their
street rods since Jaguar came out with IRS in the 60s. The concept is
simple, place a half shaft in a lathe and cut out the section needed to
achieve the desired length. Then on each end piece bevel from
the
cut edge back toward the yoke so that the shaft of each yoke ends up
with a point on it. Line the two shafts up, point-to-point in
a
piece of angle iron, making sure that the yokes are perfectly in phase
with each other, and begin filling the area between the two pieces with
weld. A competent welder should be able to fill in the shaft and return
it to a solid piece. Using this technique results in maintaining a
solid shaft just as the unit was originally designed, and the welded
section will probably be stronger than any other part of the
shaft. However, there are two difficulties in this
technique, one, getting the yokes lined up, and two, ending up with a
straight half shaft that is not slightly bent or warped. If
the
half shaft yokes are out of phase even 1 or 2 degrees or the shaft is
bent, the slight variation will result in horrible vibrations and/or
broken u-joints. Assuming everything is correctly welded,
together this technique has proven to be strong and reliable.
Red
lines show beveled cuts and
the green area is the weld
Turn
down, cut, press & weld:
Another option is
to use the yokes from
the solid half shafts to make a mechanical tubing type half
shaft. This is done by turning down a section of the half
shaft
near each yoke end to a size that will be a .002 to .01 press fit in
the mechanical tubing that will be used to connect the two
ends. Then cut the yoke ends off of the half
shafts,
leaving about 1”- 2” of turned down shaft attached
to each yoke.
As mentioned, thick wall mechanical tubing cut to the correct length
will join the two yoke ends together by means of a press fit as well as
a bead of weld around the base of the yoke and mechanical
tubing.
One major advantage to using this technique is by converting to a
tubing type shaft, weight is shed and, if repairs are needed in the
future, they are simple to do just as you would with any other tubing
type drive shaft. You may wonder how tubing could be strong
enough, especially when you consider the original shafts were solid,
but the reality is that the modern materials used to make thick
wall mechanical tubing are stronger ounce for ounce than the materials
used to forge the original shafts and the strength is probably fairly
close, if not better, on the modified shafts. This option is
usually less expensive than the one mentioned above because it is
easier for a driveline shop to index the yokes and avoid having the
half shafts warp. After discussing the options with several
machine shops, as well as others who had narrowed a Jaguar rear end, I
decided to have my shafts narrowed via this technique for both cost and
reliability. NOTE the larger
the diameter of the mechanical
tubing used, the stronger the half shaft, just as an example, a tube
1.75” O.D. is almost 4 times stronger than tubing of the same
wall
thickness with only a 1.25” O.D. Also, for ideal
penetration
while still maintaining strength, 1⁄4” wall tubing
will be best
for this application. Several
aftermarket companies that
narrow
up Jaguar rear end assemblies use 1.75” O.D. and
1.25” I.D. DOM
mechanical tubing.
Red lines show
modified yoke
ends, blue lines represent mechanical tubing, and green lines represent
the welds.
Fabricate
from scratch:
Another
option is to have custom half shafts made from new yokes or used
drivelines. The yoke on the Jaguar half shafts is sized for a
standard Chevy u-joint so new yokes can be used or used Chevy drive
lines can be cut down to fit between the differential and the
hub. The advantage to this is a solid quality piece in many
cases
made from all new components. The down side is using drive
line
yokes will make the shafts wider than the original half shafts, which
my require spacing out the coil over shocks so that there is clearance
between the springs and half shafts. Also, finding used Chevy
drive lines that are around 2” or less may be difficult and
when I
looked into ordering new yoke ends, it was going to cost me over
$100.00 a piece just for the yokes, not including the machine
work. That is the main reason why I chose to have the
original
half shafts used to make the yokes.
This is what my
shafts looked like after they were narrowed at a local driveline shop.
After this picture was
taken, they were sand-blasted and powder coated.
Narrowing the
LCAs:
Narrowing the LCAs
is easier than the
half shafts in that it can be done at home but don’t let the
DIY aspect
of the process overshadow the importance of narrowing them
correctly. Half of the rear end weight will be on each of
these
half shafts and making sure they are narrowed properly is
critical. Paying attention to the details and knowing the
limitations of your skill set will ensure this process is completed
correctly.
Taking
measurements and
making indexing
marks:
The first thing
that needs to happen in
the process is to take a whole bunch of measurements so that you know
exactly what the LCAs looked like prior to modifying them. YOU MUST do
this step because, if you do not, you will not have any frame of
reference as to how long things need to be. Once you think you have
taken enough measurements, take a few more. Not only take
measurements and notate them but also notate where the measurements
were taken from so you can measure for the exact same points when
measuring the mocked up pieces after material has been
removed.
Another wonderful point of reference is to make indexing marks on the
side of the tubing so that when you put it all back together you can
check to see that the lines are lined up and know that everything is
being put back together correctly. To make lines, place a
piece
of angle iron on the LCA tubing and score a line along the side of the
angle iron on the tube. I only did 1 indexing line per
LCA.
Make sure the line is longer than the section of material to be removed
so that it will be on both halves after the material is removed.
I am measuring from
two fixed
points on the jig while it is installed on the unnarrowed LCA
You
can see the indexing marks line up perfectly, even after the LCA has
had
a section removed.
Building
a LCA shortening jig:
Once you have
measurements, it is time
to build a jig. (Homemade Tool # 3) I built mine by starting
with
the pivot mounting holes. When building the jig, I set the
LCA on
the table with the flat machined surfaces of the LCA facing up so that
I could use them as surface for the jig to fit up against. I
cut
small pieces of steel that could be bolted to the outside of the pivot
points on the LCAs. On the hub end of the LCA, two
.625” bolts
were used, but on the differential end of the LCA, I had to come up
with a spacer and went to the hardware store with my digital calipers
in hand. What I found that had the correct O.D. was a plastic
5/8” pipe coupler. The O.D. was perfect but the
I.D. was still a
little big so I took a lug nut, drilled out the threads and rounded off
the corners and then pressed it into the coupler. This gave
me a
perfect .5” hole in the center to bolt the jig to the
LCA. Once
each arm had a sidepiece bolted to it, I connected the two sidepieces
together with a sold piece of steel that was clamped to the arms up
against the machined surfaces and then welded the connecting piece to
the sidepieces. This creates a solid bolt-in mount for each
end. I then cut two short pieces of angle iron and rounded
the
outside corners so they fit perfectly inside a longer piece of angle
iron. After that, I placed the two pieces, one on each end,
on
the LCA and connected them with the longer piece of angle iron clamped
with hose clamps to each one and the LCA. The next step was
to
weld connectors between the two short pieces of angle iron and the
bolt-in mounting ends. I used scrap that I had on
hand. The
concept of this jig is that once made it can be removed, and then the
LCA cut, the two halves can be bolted to the two halves of the jig and
by using the longer piece of angle iron and the hose clamps, the two
ends can be held perfectly in place, indexed correctly, for tack
welding. Once the jig is made, bolt it to the LCA prior to
cutting and find a place to measure on the jig. This will
give
you one more reference point when measuring the position of the two
halves to ensure that you end up with the correct length LCAs.
These
are the two halves of the narrowing jig. Half
of the jig is installed on half of the LCA with the connecting angle
iron clamped to it.
Cutting
the LCAs:
In order to narrow
up the LCAs, you will
need to cut out a section of the tubing. The professional way
to
do this is put the LCA in a lathe and use the lathe to cut
it.
This takes a large lathe and probably the services of a machine
shop. In the pursuit of maintaining a DIY project, I devised
a
way to do it at home. I started by setting both LCAs side by
side
and made a mark on the differential end of each LCA where the cut would
be, so that the cuts would be the same on both LCAs. I then placed tape
around the tube so that I had a nice straight line to follow, and then
measured the distance I wanted to remove and applied a second piece of
tape at that measured distance. Using the edge of the tape, and being
careful not to damage it, I took a triangular file and made a small
grove along the edge of the two pieces of tape. This gave me
two
groves 2.25” apart. I know you are thinking the
half shafts were
only narrowed 2.125” and we will discuss the discrepancy
later in this
article. I was then able to use a large 3-blade pipe cutter
to
cut out the 2.25” section. The reason I cut the
groves with a
file first is I have found that it is easier to use a large pipe cutter
and get an accurate cut if there is already a groove for the blades to
rest in.
Tape can provide a
perfect edge
to follow when
cutting a grove.
A large pipe cutter
makes
cutting a section out of
the LCA simple.
Getting
the pieces indexed and measured for welding:
Prior to welding
the halves together,
the jig will need to be installed, measurements will need to be taken
on both the arm and the jig to ensure the correct length and the
indexing marks need to be checked. It is also a good idea to
lay
the parts out on a flat surface and make sure that the distances
between the eyes of the LCA and the flat surface are the
same.
This will ensure that both ends of the LCA are correctly
indexed.
I measured mine by making sure the hub end was shimmed so that the
centers were the same distance to the surface and then measured the
distance between the machined surface and the table on the differential
end. I shimmed the hub end and measured the differential end
because the wider differential end will show greater differences than
the hub end, due to the extra width. When I measured mine,
the
jig only allowed a.02” difference, which probably would have
been fine
but I couldn’t let it go and adjusted it by loosening the
clamp on the
differential end, tapped the arm lightly with a hammer, measured again
and, once the measurements were identical, tightened the clamp back
up. With everything held in place, the half shafts are ready
to
be welded.
Once
the two halves are installed in the jig, measurements need to be taken
to
end up with the desired length.
Using a flat
surface and a set
of digital calipers allows the two halves of the arm to be indexed
perfectly.
Welding
the pieces
together:
As
with the half
shafts, there are
several schools of thought, and thus, different options on how to best
accomplish the task of joining the two halves back together.
Prior to narrowing my LCAs, as with the half shafts, I did
much
research and came up with three techniques/options for welding things
back together : “Bevel & butt
weld”, “Sleeve” and
“Gusset”.
Bevel
& butt
weld:
The first
technique is not only the
method used when the LCAs were original made, but also part of the
other two options. Once you have cut into the LCAs, if you
look
inside the tube on the differential end you will see weld slag where
the forged steel end was welded to the tubing. This is
nothing
more than a butt weld and a butt weld is a sufficient way to join the
two halves. For best results, however, bevel the edges to
improve
penetration. With the halves in the jig, you should notice a
.125” gap
between the two pieces from cutting out more than the 2.125”
the arms
will be shortened, and this is there to be filled with weld and create
a better penetration and a solid joint.
To the right we have
the inside of the LCA. Notice the ring
of
weld slag
that is the result of the forged steel end being butt welded to the
tubing.
Sleeve:
An improved option
over the butt weld
option is to also sleeve it and then butt weld. By cleaning
up
the inside of the tubes, you can machine a tube to fit inside and help
line things up. This will keep the tubing straight and add
quite
a bit more strength. This also allows for plug weld holes to
be
drilled through the LCA tubing on the arms so that more than just the
butt weld can hold the sleeve to the arm and gives you another place to
make tack welds.
Sleeves sized to fit inside the LCA tubes.
Sleeve installed in the LCA.
Plug weld holes in the LCA tubing.
Gusset:
Yet
another improved option over the
butt weld technique is to also install gussets after butt welding the
two halves together. The gussets will overlap both the
original
butt weld joint and the new butt weld joint on each side and provide
another way to connect the two pieces together. Also, this
improves rigidity of the LCA and completely eliminates any LCA
flex.
The
way I see it is if I am going to have gussets, I might as well make
them
look good!!
Not being one to
do things in a less
then over built way, I chose to use both sleeves and gussets. Adding
the gussets not only added strength but also afforded me the
opportunity to have some really cool lightening holes cut
out.
When I put these together, I tack welded the two halves of the LCA
together and then took them into a professional welder to be welded up,
including the installation of the gussets. NOTE as
I said
before I am a competent fabricator, however, the greater part of what
makes me “competent” is knowing when the task that
lies before me is
beyond my skill set. Could I weld up the LCAs, yes, would
they be
strong enough, probably, but why run the risk of not having
professional quality welds when it would not be that expensive or time
consuming for me to take the tack welded arms to a certified welder and
have them finished up.
Notice
the deep channel between the two halves of the LCA with the sleeve in
the middle, this channel will fill with weld and allow for excellent
penetration. Also notice the tack welds in the channel and plug weld
holes.
This
is what the LCA looked
like after I
tack welded it. Since the gussets will go
over the plug weld holes, they will not be installed until the plug
weld
holes have been filled and ground smooth.
Here
we have the welded up LCAs complete with running horse gussets. These
are the correct length, should be stronger than the originals, and a
little powder coating will make them look incredible.
Changing
the bolt
pattern:
When
it comes to
wheel bolt pattern, if
you are trying to put a Jaguar IRS in a classic Chevy, you have it made
because the Jaguar bolt pattern is the same as a classic Chevy, 5 on
4.75”, but if you want to put one of these units in a classic
Ford, the
bolt pattern is different, Ford uses a 5 on 4.5”
pattern. As with
other aspects of this project, there are several options in dealing
with this issue. The first is to run different pattern wheels
on
the back than on the front. Problem with this is that you
need to
carry two spare tires. The second option is to use hub
adaptors
that change the bolt pattern. This option is not ideal
because
bolt pattern adaptors are .75” to 1” thick and, if
you are planning on
this option, the unit will need to be narrowed even further.
Also, adaptors like this sell for around $50.00 a pair.
Another
option is to buy the correct bolt pattern wheel flanges from places
like CWI. They sell hubs that have been modified and have the
correct bolt pattern machined into them. This option gives
you a
quality flange with the correct pattern but has the down side of being
fairly expensive.
I didn’t
really like any of these
options and, there again, was striving for this to be as much of a DIY
project as possible, so I decided to drill out the pattern
myself. When I first suggested to some other car enthusiasts
that
I was planning to drill the pattern myself, I was told not to drill the
pattern because it would be almost impossible to have all 5 holes be in
the correct spot. I pondered the issue and, at
first,
thought about making a 10-hole jig. (5 holes each
pattern)
Problem is, I still would have a hard time getting all 10 holes in the
correct position. One day while contemplating this issue, I had an
epiphany, instead of making a 10-hole jig, make a 3-hole jig and rotate
it from position to position. I made the jig (Homemade Tool # 4) by
drawing 2
circles, a 4.75” circle with a 4.5” circle inside
it. I then
measured the distance between two studs on the Jaguar wheel flange and
plotted those 2 points on the outer circle. Using these two
plotted points I measured between them and plotted a center point on
the inner circle. The drawing was then transferred to a piece
of
steel and the three holes were drilled out, .5” inches on the
outer
ones and .125” for the center hole. The jig can now
be bolted to
the flange and a pilot hole drilled. The beauty of this jig
is
that even if the pilot hole is not perfectly centered, as long it is on
the 4.5” circle, it will be in the same location between the
two studs
on all 5 holes, giving a perfect star pattern. After creating
the
jig, I purchased a cheap Chevy rotor and drilled out the Ford pattern
to ensure that the jig was accurate prior to drilling the hub.
If you would like to purchase
a CNC cut 3-hole bolt pattern Jig rather than make your own I now offer
them for sale. To purchase one click here
Finding
wheel studs:
Before you can
drill your wheel flanges,
you need to purchase your wheel studs so you know what size to drill
the holes. Finding the correct press fit wheel studs can be a
challenge, due to the fact that moving the holes in
1⁄4” moves
them very close to the machined surface on the backside of the wheel
flange. With that in mind, the new press stud holes need to
be no
bigger than 17/32”. Most 1⁄2”
wheel studs have 9/16” – 5/8”
Knurl Diameters and so would be too big for the application.
To
come up with the correct stud, I went to my local tire and wheel
supplier with my digital calipers in hand and asked to look through
their wheel stud selection. I found a stud that has a Knurl Diameter
0.558, which makes it a perfect press fit in a 17/32” hole so
I
purchased 10 of these for my project. At the time, I was not
able
to cross-reference the part numbers I had for the studs to find out
what they were normally used for. Some time later, I went
back to
get 10 more for another Jaguar assembly I have that is going in my 62
Galaxie and could not find the same studs so I found another stud that
would work. The new one has a Knurl Diameter of 0.536 making
it
an ideal press fit for a .5” hole. Not being able
to find the
original stud concerned me, in case I ever needed to replace one, so I
once again began a search for what application either of these studs
were designed for. This time I was successful and
the first
set of studs I purchased are Dorman part #98141 used on the 1980-1983
Ford F-100. The second set of studs I purchased are Dorman
part
#610258 used on 1998 Jaguar XJ8 and the 1967-1978 Cadillac.
3-hole jig, two in
the Jaguar
pattern and one in the Ford pattern. To buy a CNC cut jig click here
The jig
bolted to
a cheap Chevy rotor to test it and ensure that it was accurate
Once I had my jig
built and I had my
wheel studs so that I knew what size to drill my holes, I was ready to
modify the Jaguar wheel flanges. To do this, I removed the
original Jaguar wheel studs by grinding of the back crimped edge of the
wheel studs and unscrewed them. I had to install old lug nuts
onto the studs and weld the nuts to the studs in order to use a breaker
bar to bust them loose. The threaded holes left by the wheel
studs were ideal to bolt the jig into place. With the jig bolted in, I
drilled a pilot hole and then positioned it on the next two studs,
making sure the same side of the jig always stayed up. I
drilled
the pilot holes one bit size at a time up to .5” all the way
through
and then 17/32” halfway through from the backside to
accommodate the
.558 Knurl Diameter of the new studs. Prior to using them I
modified the press studs by trimming of one edge so that there was
proper clearance between the studs head and the hub housing.
I
then pressed the studs into place. This gave me wheel flanges
with the correct Ford bolt pattern.
New studs installed in the Ford bolt pattern, with the original pattern
holes left open.
Stud with one edge ground off for clearance.
Notice the two sized 1/2" at the bottom and 17/32" at the top to fit
the press studs.
The hub is a perfect fit in this 5 on 4.5 bolt pattern rim
With everything
modified for the
purpose of narrowing the unit and the correct bolt pattern drilled,
this project can now go into the assembly phase. In the next
article, page
IV, we will look at the differential rebuild, drive shaft
rebuild, and the rebuilding of the hubs.
BUT if you can't wait to see what a Jaguar IRS looks like
under a classic Mustang check out Mustang IRS
Success Stories
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.