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The Ford Differentials by
kevinstang.com
Thanks to Kevin for sharing this info with GearHead
Racing
Introduction
The most popular rear end around
is no doubt the Ford 9 inch unit, it is used by restorers, street rodders and
racers alike, regardless of what brand of car the axle is going in. Many custom
made axle housings for the GM boys utilize the 9 inch Ford, even though they
hate to admit it. Ford used the axle from around the 1957 model year right up
until the early 1980’s in cars and trucks. It was not the only axle used, but
was by far one of the best. Variations by Ford exist in the size of the outer
axle bearings in the housings and carriers both, as well as with the spline
count on the axle shafts. Generally most cars received the small axle bearings
and 28 spline axle shafts. Exceptions to this were the ultra Hi performance Boss
302’s, Boss 429’s, 427’s, 428 CJ/SCJ and the 429 cars which received the
31 spline carriers and axle shafts. Some of the heavier cars like the Galaxies
also received the larger wheel bearing housings. The trucks varied more, early
half ton trucks got the 28 spline axles and carriers, while sometime in the
early 70’s the switch was made to mostly 31 spline axles and carriers for most
trucks. Most of the later trucks also received the larger axle bearings
housings. One exception to this was the Bronco’s from 1966 to 1977, they
stayed with the 28 spline units. A small bearing housing can be differentiated
from a large bearing housing by the size of the nuts and thread used to retain
the brake backing plates to the housing, the small bearing housings use 9/16
socket size nuts with 3/8” fine thread, while the larger bearing use 11/16”
socket size and 7/16” fine thread. Gross Vehicle Weight ( GVW ) would
determine which axle housing many cars and trucks received.
Because many one half ton trucks continued to utilize the 9 inch (both 2 wheel
& 4 wheel drives) right up until about 1982 these housings are by far the
most abundant(*Note:my recent findings are that the 9 inch axle was either
utilized again in limited quantities in some 1985/6 truck/van applications or
continued to be used up until that time by Ford in limited quantities*), and
with many 1973 to 1979 pickups to still be found on the road and in junk
yards,these are the most plentiful. And since the “Limited slip” or Locking
rear end (often referred to as a “POSI”) came to be a popular option and
more plentiful starting in the early 1970’s, many of the units found today at
car swap meets and shows are the units pulled from trucks with the 31 spline
carriers with the “Traction Loc” style posi unit. The actual car posi units
which were primarily 28 spline carriers can be much more difficult to locate
since the supply is limited to the few cars and early Broncos (and some early
trucks) which received them-the 28 spline posi’s.When it comes down to actual
shafts as well, since the truck lug pattern in most cases differed from the car,
and due to the bearing size differences, 28 spline car axle shafts are much more
abundant than car 31 spline axle shafts, and often aftermarket shafts have to be
purchased if one wants to use a truck 31 spline carrier in a car :(
The carrier housing I see most is the C7AW-E, it is the one most commonly found
in the trucks right up until around 1982. I am not sure if this “E” version
of the case came into use in 1967 or in subsequent years, but it is by far the
most abundant case being used in both full size Ford cars and trucks throughout
the 1970’s. I have heard that it has a higher nodular iron content and better
casting than the earlier single ribbed cases it replaced and that is why it
remained in use so long, and the double ribbed N case was no longer needed for
passenger car/truck applications (this also coincided with the demise of most
performance engine options in the 70’s)- I have never seen this substantiated
however. Most carriers I have seen for sale at swap meets/ car shows are this
C7AW-E case which leads me to believe most were pulled from trucks and cars from
the 1970’s.
Axle housings as noted in the examples below also evolved over the years, the
earlier housings used in cars from 1957 to mid 1960’s tended to be the weakest
and had abrupt ending but welded carrier centers to tubes and a smooth backside.
Later housings appeared in either 1966 or 1967 with the familiar “Hump” in
the backside middle and stronger tubes.The later truck housings received even
beefier center carrier housings and tubes and this style of center carrier
housing is best suited for drag cars or narrowed rear ends in my opinion due to
the added strength in the middle. Most of the early housings are ok for the
average street performance cars. The popular early swap being the 57 to 59 Ford
for the 65/66 Mustang.I haven’t completed an axle housing width chart yet, but
here is what I can tell you about some that I have seen, they often group
Mustangs and Fairlane axle housings together as often it is true they are the
same width, but I can tell you for a fact, the distance between spring perches
is different between Mustangs and Fairlanes.Spring perches must be cut and
re-welded inorder for the swap to be performed. The “rough “ widths I keep
in mind for Mustangs are the following: 52” for 1965 to 1966 (the same width
as 64-65 Falcons and 62 to 65 Fairlanes-as in the Mustang line, most however
never received a factory 9 inch), 54” for 1967 to 1970 (same as 66 to 69
Fairlane,Torino,Comet & Cyclone non station wagons-cars with 351 and up
engines received 9 inch units-as did some 302 4V cars with optional gear ratios)
and 56” for the 1971 to 1973 Mustangs-cars with 351 engines and up receiving
the 9” housings.Keep in mind as mentioned, the Fairlane spring perch distances
were not the same as the Mustang. All the Galaxies I have seen from throughout
the 1960’s used the 9 inch rear, regardless of engine size.
How to Identify some typical Ford Centers
Let's start with the 9"
First off, the 9” is a removable carrier type rear end, it shares this design
in common with it’s baby brother the 8”, while the 6 ¾”, 7 ¼’, 7.7”
, 8.8” and Dana rears also used in Fords are integral carrier types. Both GM
and Mopar also had earlier removable carrier type rear ends, they are no where
near abundant as the Ford. Removable carrier means these are front loading
differentials, they have no cover / inspection plate on backside-the 8.8's etc
are considered rear loaders. When a gear ratio change is desired, a entire
carrier assembly (previously assembled) can quickly be installed by simply
pulling the axles and drive shafts, then undoing the ten center retaining nuts.
Quick ways to identify a 9” visually:
From rear of car look for a large center hump in middle of backside center
section (post 66 models), in general a round appearance, it is a 9”.See photo
above.
From front side look at the bottom two center retaining nuts, if a socket cannot
access them to remove, only a wrench, then it is a 9” See photo below.
There are several distinct case types used over the years for the 9” carrier
(shown above are the 3 basic)…lets start at the beginning with the infamous
WAR case...
I have heard various stories as
to the reliability of the WAR marked cases, some say avoid them like the plague,
others say this is false.Here is what I understand, while having the extra
ribbing like the later N case, they do not have the nodular iron content and are
prone to cracking at the bearing support.They seem to have been used on the 57
to 60 Fords from casting dates I have seen.
Another early case, the WAB was similar to the WAR case with the double rib and
lower nodular content. I do not have a photo example at present.I believe this
case utilized the larger 3.063 side bearings.
The C7AW-E case seems to have been the standard case in use for quite sometime,
have found them with date codes up to 1981.Other standard cases encountered:
C1AW-4025-C,C4AW-4025-A
Some standard cases are also machined to take the larger 3.063” side bearings,
most cases however (including N cases) will take the 2.892” side bearings.
Aftermarket spools and cases are available that accommodate even larger
bearings-3.250" and 3.812", but Ford used just the two sizes from what
I have seen.The carrier I have seen with the 3.063" larger side bearings is
the C7AW-G marked single ribbed case, it came from a late 60's Galaxie.
THE N Case vs WAR Case
"Standard or WAR cases, were cast in gray cast iron which has a grain
structure that does not have the best shear strength characteristics. The N
stands for nodular iron, which is made by adding magnesium to molten iron. What
this does is change the grain structure from flakes to nodules - much stronger
and less likely to fail under shear load." - contributed by Paul Bartus
The case of course most desirable is the N case, first used on the 427 Galaxies
around 64-65 I believe.They are most often found behind the later 428CJ and
429CJ cars.From what I have seen don't expect to find them in 390 or 289 Hipo
cars.The N cases went with 31 spline centers and are for rugged duty.And believe
it or not, they were also used in some FE equipped Ford 1/2 ton 4X4 pickups!
Here is the early N case, the C4AW-B casting, which can either have the N or
not.Some N cases will also have the bearing caps marked with an "N",
some do not.
Have also viewed a N case marked with an "N" with a C2AW-4025-A
casting number,it was used in conjunction with a C5AW-4668-C Daytona pinion
support.Case was double ribbed, this casting number is not listed in my books or
references, will have to do further research regarding this one.
Pinion Supports
Other standard pinion supports encountered: WAT B2(on a WAR
case),C0AW-A,C6AW-4668-A,C7AW-C(guarded support as well) and a
D2SW-4668-C(marked with the 4668).The D2SW-C seems to be the most common
encountered through 1979 on the C7AW-E cases I have viewed.
Earlier daytona pinion supports: C5AW-4668-C
Now the 9 1/2" story..
Here is something else you may run across, a 9 3/8" ring gear
housing(sometimes called a 9 1/2" Ford carrier),I don't know much about
them, but looking in the book they appear to have come in the larger Lincoln and
Mercury vehicles.Note casting number C8AW-4668-B on pinion support and the
double ribs(spaced further apart) with the end bent down on one.From what I
understand parts from these rears do not interchange with the 9 inch carriers.I
have heard they can be installed in a 9" housing if the housing is notched
for the wider gear and the gasket for the 9 3/8" is used (bolt pattern is
supposedly the same).I have started to see a few of these in some Ford pickup
applications, mainly 4X4 with a trac loc option and FE motors.The truck
applications seem to have some better ratios than the passenger car
applications.All the applications of the 9 3/8 I have seen have been 31 spline.
Here is some 8" info:
The casting number should be
C2OW-4025-F, NOT C2DW listed for the case.Another later 8" pinion support
with guard built in that I have seen had casting number C6OW (the 6 however may
have been a 5-this support came out of a 65-66 mustang center).
Later improved carrier for the 8" found in 67 and up
Note the presence of fill plug, and that the casting number is moved to the
outside of case, while other previous 8 and 9 inch carriers it has always been
on the inside.The number here is the familiar C7OW-4025-A.
Visually Spotting the 9" and 8"
Axle Housings
Shown above is the typical 1967
and up 9" (lower) and pre-1967 8" housing (upper).Note no fill plug on
back of the 67 and up housing, this is true for the 67 and up 8 inch housings
too.Earlier housings, like the 65-66 Mustang 8" pictured have the fill plug
in the back, this is true for the earlier 9" as well.
One of the ways many people spot a 9" rear end in the car is by looking for
the hump in the center of housing, this is not always the best way, as 9"
housings made prior to sometime in 1966 do not have the this large center
protrusion.The one shown above is out of a 63 Galaxie, note its roundish
appearance, two dimples and fill plug in housing back.
Here is the housing style familiar to most, note the large center protrusion or
simply the "hump" in the middle.Housing also has the two dimples, but
note lack of fill plug.This housing is out of an early Bronco.
The little brother to the 9" housing is the 8" housing, note its more
oval appearance when compared to the above two 9" housings.This one is out
of a 65-66 Mustang, note the two dimples and fill plug.
Another area of concern when swapping axle housings into earlier Mustangs (65-66
models especially)is the diameter of the outer axle tube.Note the taper on this
8" 65-66 Mustang housing, a smaller U bolt and lower shock plate were used
originally with these cars.The HIPO 289 cars were the only 65-66 Mustangs to
recieve factory 9" axles, the tubes are tapered as well at the end to
utilize the same lower shock plate as the regular 65-66 Mustangs.
Notice this axle tube has no taper at end,as is typical for most housings.A
typical early Mustang swap is a later Granada housing, were the non-tapered tube
can become an installation problem at times.
Axle Shafts
Shown above is a 31 spline shaft end in a 69 Cyclone CJ
Ford used either 28 spline or 31
spline axle shafts with the nine inch, the eight inch came only in 28 spline, as
did the majority of nine inch car applications.For the most part eight inch and
nine inch car axle shafts will interchange between housings of the same
width,spline count and bearing size (ie. 8" 67 Mustang 28 spline axle
shafts will work in 9" 67 Mustang housing, etc.).A method to identify 28
spline axle shafts can be by looking at the center brake hub area, a rectangular
slot in the center will indicate 28 spline axles.The 31 spline axle shafts will
have a different appearance, with one small center chamfer and two outer holes
in the center hub, however, 28 spline shafts can also appear like this to, so it
does not always indicate 31 spline shafts (see photo below). Early axle shafts
of the 28 spline variety cannot be shortened, due to either a reduced diameter
between spline end and bearing end (early Mustangs,Fairlanes, Falcons etc.), or
because of a tapered shaft which doesn't allow for re-splining (early full
size).It appears starting around 1967 the 28 spline shafts became more solid and
the shaft diameter increased along the entire length, so shortening is possible
and they can be be resplined to their original 28 count.Most 31 spline shafts
can be shortened and resplined with no problems.
Rear Axle Tags
Rear axle tags if present on your
housing can aid in identifying what is behind your center for gears,splines
etc.Ford has changed the tag over the years, but generally the appliction
number-which begins with the W on line one, the gear ratio and date code are
always given.Tags are generally found attached to the passenger side of carrier
assembly secured by one of the nuts on the housing studs.Here are some examples
I have:
Here is the early style tag used by Ford, this one is off a 62 Galaxy with a
3.00 open 9 inch.Tag reads C2AA4001 DV 100,second line:: 3.00 1MA
Here is a common Mustang tag WCZ-V identifies it as a 67-70 Mustang and 67-68
Cougar 8" rear with 2.79 ratio, open.Note no L between 2 and 7 on second
line.
A "posi", equa-lock or traction lock rear is identified by an
"L" in between the 1st and 2nd digits of the ratio given on the second
line of tag.Here is a 2L80 ratio with tag number WDJ-B,which corresponds to a 8
inch used in 65-66 Mustangs.
This tag is off an open 3.25 ratio 66-70 Fairlane or 67 to 69 Comet with an open
9 inch differential.Note date code of 7BD ( 7= model year:1967,B= Month:February
and the D= week: 4th week of Feb.1967)
Ford changed the layout of the tags sometime in the early 70's or late 60's,
here is a WFE-BK2 tag, followed by a date code of 4E24 (April 24,1974), the
second line now gives besides the ratio-here a 3L50, the ring gear actually used
inside-this one is a true 9" gear.This tag is off a 74 Ford truck.
Here is an example tag of a 9 inch that isn't quite up to the full measure,it is
a 3.50 ratio, but followed by that are the numbers 8.7 which denote that this
carrier is sporting a ring gear of an actual 8 3/4 inch diameter.This one is off
a 1970 Bronco, built 3rd week of April 1970.This would have been a 28 spline
unit when checked in manual.
How to identify a “Posi”
The two basic types of “posi”
units (posi is the G.M. name for its positive traction system which has been
become a part of the nomenclature) are the early Equa lock and the subsequent
Traction lock units ( I will refer to them here as “spools” to simplify
things). I am not exactly sure when the Equa-locs first appeared, early units
are scarce – I haven’t seen many prior to 1964/65 and these are quite
rare.From what I have seen the Equa locs were used up until 1969, which is when
I believe the Traction Loc units first appeared. There are visual and internal
differences between the two spools and most parts do not interchange.
Shown above is an example of an equa loc in its carrier, you will note the
recessed bolt holes and 5/8” headed bolts, as well the rough cast appearance
of the cover assembly, it is not machined as it is in the Traction Loc units.
Internally the number of clutch disc and plates differs between the equa loc and
trac loc spools, the equa loc having only 3 fiber plates and 4 steel with one
large belveder spring applying force.The trac loc unit utilizes 4 fiber plates
and 5 steel plates, with 4 smaller springs applying force.Both equa lock and
trac loc units were available in 2 pin and 4 pin varieties, in either 28 spline
or 31 spline versions.The four pin 31 spline unit would be more commonly found
as a trac loc piece. The four pin being the heavier duty unit utilizing 4 spider
gears vs just two in the two pin variety (as noted in figure above a four pin
variety will have actually just 3 pins and a two pin will in reality just have 1
pin- the number of spider gears is actually what is being referred to).Shown
below are the internals of a four pin equa loc, note the five “fingers” on
the steel clutch plates-the tiny circular tabs on outer edge- (trac loc units
will have only 4).
The traction loc
Shown above is an open 28 spline spool (on left) and a traction loc “Posi”
28 spline 2 pin spool ( to the right).
Here is a close up of the trac loc spool, note recessed bolt holes through cover
for holding ring gear on.
Notice the flat surface around holes on the open spool.
The heads of the bolts which pass through cover and fasten ring gear to the
spool are also smaller on the trac loc piece 5/8” socket size, and they use a
thin metal washer.
The bolt retaining ring gear on the open spool is 3/ 4” socket size, no washer
used.
Above are a 28 spline 2 pin traction loc unit and a 31 spline 4 pin trac loc
unit, notice anything wrong?
The arrows are pointing to the cracks in the 31 spline unit removed from an N
case carrier.
Unfortunately this is the end result, a destroyed posi unit, this is even the
improved cover – D0O part number, earlier units were even more prone to
cracking here, thus the necessity for the Detroit Locker units used behind many
of the higher performance applications.
Gears, Yokes etc.
Here are two nine inch ring gears
side by side, one from a 3.00 ratio (thinner gear), the other from a 3.50 ratio
(thicker).An easy way to spot a nice ratio after a while is by visual id.-the
thicker the gear the better the performance ratio, thinner the gear= less
performance, more fuel economy and better highway performance.
These two gears are the same ratio- 3.00, but one is only 8 3/ 4” diameter,
the other a true 9”.When gear is installed in the case, a true 9" ring
gear will have very little clearance between housing and large gear (most
noticable at bottom), while an 8 3/4" setup will have almost enough room to
put your finger tips into between gear and case (but don't due it- it can
hurt).Don't feel slighted if you find you only have an 8 3/4" setup, they
are plenty strong, Ford used them behind the HiPo 289 applications in many
Mustangs and others.
Can you spot the difference in the above two pinion gears? Both are 10 tooth
gears taken from 3.50 gear ratios, but one has been used behind a Daytona pinion
support with the larger inner bearing (see above sections for discussion on
Daytona pinion support identification).Note the larger bearing on support to the
left.
These two yokes are quite similar and take the same U joint, except the shorter
one is used with the larger bearing Daytona Pinion used in an N case. I believe
the shorter yoke was necessary due to the added size of inner bearing.When
installed on there respective carriers, supports equal out to approximately same
height.I am told that the standard yoke can be machined down to work with the
Daytona pinion.
Crush sleeves are used when setting up most 9 inch carriers to set bearing load,
but on the N case with Daytona pinion a non-crush solid spacer is used, shown
above are the two side by side (solid spacer on right).
This page is far from the gospel, it is put together out of my experiences in
searching out Ford rears over the last years and with the help of others.It will
hopefully be a good visual guide to the various differentials used in the older
Fords.I will most likely add sections as time permits and expand upon some of
the above as I gain more insight.Eventully I may add some of the smaller
integral carrier information as well.
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