you've ever wanted to know
about Ford 9 Inch Differentials!
and photography by [email protected]
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.
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,
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.
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.
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 nickel
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.
to Identify some typical Ford Centers
start with the 9"
Pictured at right, are the most common to the most desirable 9 inch
Ford differential cases.
The C7AW-E case seems to have been in use for quite sometime, have
found them with date codes up to 1979.Other standard cases encountered:
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 N case,
they do not have the Higher nickel 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.
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!
is the early N case, the C4AW-B casting, which may either have
the "N" casting mark or not.
"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.
"N" case marked with a "N" below the bearing
cap support area, D0OW-B casting.
word on side bearing sizes
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