Q. What
do you get
if an 8" rear end housing from a 1966 Mustang and a
9" housing from a 1969 Country Squire meet in my garage??? A. 9"
housing with
small tubing housing ends for a 1964.5-1966 Mustang
Why
upgrade to a
Ford 9”:
The
Ford
9” rear end is arguably one of
the best OEM rear ends ever produced. Please don’t
misunderstand,
there are other really good rear ends out there including, but not
limited to, the Ford 8” and the Dana series rear ends
produced by
Spicer, but the Ford 9”, due to its drop out carrier,
incredible
strength, availability, more gear ratio choices, not to mention more
locking, limited slip, and spool options for the carrier, has made it
the rear end of choice for builders for hot rods and drag cars of all
makes and models, including the Ford enthusiast community at
large. The Ford 9” is so popular that all
its components
are being produced in the aftermarket and one can order a complete
setup with custom axles, custom housings and even aluminum carrier
housings. With options like this, a Ford 9” can be
purchased
“tailor made” for any application, yet the problem
is a custom unit can
be very expensive. In the pursuit of low cost performance upgrades when
it comes to the Ford 9”, there are really only three options;
you can
find an original Ford 9” housing that is the correct width or
almost
the correct width for your application, have a local machine shop
narrow up a larger housing, or you can build one yourself.
Finding
an
original
Ford housing that will work in a first generation Mustang:
When attempting
to
find a 9” for a first
generation Mustang there are several OEM housings used in Mustangs and
other models with the correct 52.25” housing flange to
housing flange
width. The first is an actual Mustang 9”
housing. A
few Mustangs actually came with the 9” housing but these
units are
nearly impossible to find and when you do find one they’re
expensive. Other Ford options are the 1957-1959 full-sized
Ford
cars, the 1975-1980 Granada/Monarch and the 1977-1980 Lincoln
Versailles. With these “other model”
donor cars there is one
immediate difference between them and an original 1964.5-1966 Mustang
9” housing and that is the Mustang housing has tapered tubing
ends. A
non-tapered tubing unit can be used in a first generation Mustang but
different u-bolts and mounting plates will be required.
Narrowing
a Ford 9”
rear end for a 1964.5-1966 Mustang
Farming
out the
narrowing process:
When I first
looked into this project, I
got price quotes for farming the project out to a local machine
shop. At the time, several years ago, I was quoted between
$175
and $250 to have a larger 9” unit narrowed up. None
of the
machine shops were overly interested in combining a 9” center
section
and 8” axle tubes so, had I gone that route, I would have had
to come
up with different axles since most 9” housings use bigger
bearings on
the axles. It’s
all about DIY:
As those of you
who are familiar with my
web pages know, I am all about DIY and finding ways to make it easier
for other to do things themselves. Therefore, my only real option was
to take an existing 8” housing and use its tubes and axles to
convert a
larger 9” housing into a 9” rear end for a first
generation Mustang.
There are several reasons I chose to do this:
1. Having the tapered axle tubing is period correct for a 65-66
Mustang, even with a 9" rear end. Of course, I only add that because it
could be a valid reason, I personally couldn't care less about "period
correct". I am putting a Jag
IRS unit in my personal Mustang,
for
heavens sake.
2. By using the "period correct" tubing, existing u-bolts and mounts
can be used so there is no need to source them.
3. Most Mustangs came with 8” rear ends so donor housings and
axles are
easy to find and relatively inexpensive.
4. The 8” axles are 28 spline, just like many of the
9” differentials,
and already the correct length, not to mention that as long as you are
not running slicks, a 28 spline axle can handle upwards of 400 HP.
5. All the other stock components such as brakes mount up
without
having to modify anything.
5. Most axle tubes from the donor 9" housing have different spring
mount locations that need to be relocated or all kinds of extra mounts
not needed for a leafspring suspension that would need to be cut off.
6. In many cases the O.D. of the 8" tubing is almost the same as the
I.D. of the original 9" axle tubing, making the mod simple.
7. My favorite reason is because it is fun.
Tools:
This project
starts like any other in
getting tools and materials together to do the job. One can
perform a mod like this with just the bare essentials such as a level,
angle finder, saw, welder, and tape measure; however, having some
specialized tools makes all the difference in the world. The
first “specialized” tool is a measuring jig from
Dutchman called a
Dog-bone. This tool allows you to install the axles in the
housing and check length without having to install the third
member. Another tool is something I had custom made at a
local
machine shop and that is an alignment jig. In the case of an
axle
housing, it is important that the wheel bearing housings line up with
the carrier bearings on the differential. If the tube is off,
the
axle will be inserted at a slight angle, which can cause premature
bearing failure. To ensure that everything was lined up
correctly, I put together a jig. I took an old
9-3/8” rear end
case, removed all the differential parts, and had two pucks, with a
1”
hole in the center, machined to fit inside the carrier bearing
caps. I then had two more pucks machined, also with a
1” hole in
the center, that have an O.D. that is the same as the two main Ford
wheel bearing sizes. To line everything up, the case is
bolted to
the housing and a solid 1” steel shaft 6’ long is
inserted through the
1” hole in the carrier pucks. Then the new axle housing tubes
can be
adjusted until the outer bearing pucks can be slid down the shaft and
inserted into the wheel bearing housings.
Centering pucks in case
Dog-bone for checking axle depth
Donor
housings:
Once you
have the
tools, you need to
find a 9” to cut up. For a heavy-duty housing,
trucks, vans and
stationwagons are really good places to look. I got my
housing
from a 1969 Country Squire. As you can see in the picture,
the
housing is very heavy duty, which is no surprise since the housing was
actually built for the Ford 9-3/8” third member.
NOTE You can
mount a 9-3/8" differential in any 9" housing by making notches in the
housing to accommodate the larger ring gear but, the good news is, the
notches will not hurt anything when a 9" is mounted into the housing so
a 9-3/8” housing CAN be used to build a custom 9”
housing. The 8”
housing has to come from either a 1965-1966 Mustang, or a 1965-1966
Maverick/Comet so that you get the correct smaller tubing
ends.
NOTE A Maverick/Comet housing is 1” narrower than the Mustang
so, if
you purchase one of these units intending to also use the axles, know
that the final 9” housing will be 1” narrower,
which may be a good
thing if you want to use wider tires.
Prepping
the 9” housing center section:
Once you
have your
parts, you can start
the process. I began with the 9” housing and cut
the un-needed
mounting brackets off of it that had been used for the coil spring
suspension under the Country Squire. I then cut the tubes off
1”
to the tube side of the original factory welds, so that the center
section still had about a 5” piece of the original axle
tubing pressed
inside and welded into place. The reason I did this was that
the
I.D. of the original 9” housing tubes was almost the same as
the O.D.
of the 8” housing axle tubes. I then stripped the
9” center
section down to bare metal.
Donor 9"housing
One thing I
decided to do to increase
the strength of the “new” housing was to drill
tapered holes through
the top and bottom of the center section tube ends just to the inside
of the original factory welds so that they could later be filled as
plug welds. Since the new tubes were being welded to the
original
tubes and not directly to the original center section, I wanted the
plug welds so that there was some direct connection between the new
axle tubes and the center section. This step may not have
been
needed but I have always felt that the best option is to always over
build.
9" center and 8" axle tubes
Plug weld holes to help tie it all together
My 9”
donor housing did not have a fill
plug because, on that particular unit, fluid was put in through a fill
plug on the front of the third member. I added one by taking
careful measurements on another 9” housing I had and drilled
a 7/16”
hole on the correct location. A file was then used to make a
flat
surface perpendicular to the hole and a 7/16” bolt was
inserted through
the hole. From the inside, I placed a 1/2” fine
thread grade 5
nut that I had cut down to be about 3/16” thick, over the
7/16” bolt
sticking through, and tightened a 7/16” nut down on it to
correctly
position the nut. Once in place, I spot welded the nut to the
inside of the housing and removed the 7/16” nut and
bolt. I then
double checked that the inside 1/2” nut was correctly
positioned and
welded it on all sides. A 1/2” fine thread tap was
then inserted
from the inside through the 1/2” nut that I welded into place
and the
7/16” hole in the housing was threaded to
1/2”. This gave me
about 1/2” inch of material that a plug bolt with a nylon
washer could
be inserted into, to seal the unit. NOTE Any welding slag and
or
small welding BB’s need to be removed from the inside of the
housing. If they are not removed they could come loose during
use
and damage your differential.
Nut welded inside for fill plug
Fill plug hole
Nylon washer to prevent leaks
Another
modification I made to this
housing was to add a drain hole. Early Ford housings had
drain
holes in the differential housing but Ford eliminated them from later
productions to cut costs. I used the same technique as above
with
a couple of exceptions. The plug bolt was 3/8”
instead of 1/2”
and a grove was cut into the nut I welded inside so that as fluid
levels dropped below the top of the nut, fluid could still drain out of
the unit.
Groove cut in to the nut for better draining
Drain nut welded in place with the groove down
A tap was inserted in the nut and the housing threaded.
Taking
measurement:
The next step
in
the process was to take
and notate measurement on the 8” housing prior to cutting it.
Before I
could actually start measuring I needed to do two things.
First,
I placed two saw horse 43” apart and then leveled them both
directions
so that all measurement would be accurate. In my particular
situation my garage floor was not level at all so I had to do quite a
bit of leveling. This gave me a nice uniform platform to
place
the housing on as I was working. Second, I took a piece of
16” X 3” X
1/8” and drilled four holes in it. The top hole to
be used in all
applications and the bottom three holes that corresponded with studs or
mounting holes on an 8” housing face, a 9” housing
face and the pinion
support on the jig case. This was done so that, at any point,
the
steel could be mounted to a housing and provide a uniform steel surface
for me to place the magnetic angle finder on to double check the pinion
angle. The spring mounts of the housing were then placed on the two saw
horses, the piece of steel was installed on the face of the
differential opening and a magnetic angle finder was placed on the
steel to find the pinion angle. I also used a tape measure
and
measured width from outer flange to outer flange, and width from spring
perch to spring perch. For my project, I actually had two 8”
Mustang
housings so I took measurements from both to make sure all was the same
and then used the second one as a reference when I assembled everything
later. After getting a clear picture of how the final rear
end
needed to end up dimensionally, I cut the tubes off of the 8”
housing
at the welds and stripped the tubes down to bare metal.
Leveling up the saw horse both directions prior to assembly
Magnatic angle finder used to find pinion angle
Comparing factory 8" housing and new 9" housing
Setting
length:
To begin
mocking
up the “new” housing I
inserted the 8” tubing ends into the 9” housing
center section and
placed the unit on the saw horses. The Dog-bone was installed
onto the face of the housing and a set of 8” axles were
inserted into
the mocked up unit. By tapping on the ends of the axles with
a
rubber mallet, I was able to line up the tips of the axles with the
opening in the Dog -bone. Also, I took measurements to ensure
the
correct 52.25” width flange to flange and the proper spring
perch to
spring perch measurement. Once I had the depth set correctly,
I
wrapped the 8” tubes with electricians tape at the place
where the 8”
tubes met the 9” center section to mark proper tube location. Setting pinion angle:
To set the
pinion
angle, I installed my
steel plate on the extra 8” housing and once again took
measurements
and confirmed my original measurement that the face of the housing
tilts up 5 degrees. You would think that you would want the end of the
transmission to point to the differential and vice versa, however, for
proper u-joint motion unseen lines extending from the pinion shaft on
the differential and from the output shaft of the transmission need to
be parallel. I then installed the steel plate on
the front
of the 9” center section and took a measurement and made
adjustments to
correctly set the pinion angle. I found it easiest to adjust
pinion angle one tube at a time, by setting one side to be correctly
indexed to the center housing section and then setting the other side
to be the same as the first. By doing them one at a time,
half
the force was needed to rotate the axle tubes.
Once I had
everything where I wanted it,
I reinstalled the axles and the Dog-bone, as well as took more
measurements to ensure that length and axle depth had not changed while
I was setting the pinion angle. After I was positive that
everything was where I wanted it, I installed the jig case onto the
front of the housing and the steel plate onto the front of the
case. I then inserted the 1” steel rod through the
housing and
adjusted the axle tubes so that the outer bearing pucks could be
inserted into the housing ends. With everything lined up, I
measure yet again, checking length and pinion angle. With
everything held in place, I removed the tape from the axle tubes that
showed the correct width and spot-welded the 8” tubes to the
9” center
section in three locations per tube. The housing then went to
a
certified welder so that a bead could be put around each tube and so
the plug welds could be filled. I am a competent welder and
could
have run the beads and filled the plug weld holes myself, however, the
$30.00 I paid to guarantee that the housing was solid was money well
spent. The long and the short of it is that the steel on this
housing is at the max thickness for my welder and rather than pushing
things to the max, farming it out simply made more sense. The
only thing left in finishing this housing was a trip to the powder
coater. Axles
and
differential information:
Any 9”
third member will fit in this
housing, and, other than gear ratios and differential types, they come
in two varieties, 28 spline and 31 spline. The 31 spline
third
members utilize stronger axles and are the only choice for rear ends
that will see more than 400 HP or will have hard launches, especially
when running slicks and or drag racing. In order to run a 31
spline differential in this housing, the axles will need to be custom
made so that they have the smaller axle bearings and are the correct
length. Such axles can be purchased from places like Curry or
Moser in the $400.00 price range. If the HP is less than 400
and/or you will not be running slicks and doing hard launches, such as
in drag racing, then an original set of 28 spline axles will work just
fine and can be taken from the same rear end that donated its housing
tubes.
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.