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,later Tbirds and mid 70's Torinos 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 trucks while some vans remained 28 spline. 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 and in mainly small bearing housings, although some of the later 74-77 it seems started getting the heavier axle housing with large bearings. 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 3/4” socket size and 1/2” fine thread. Gross Vehicle Weight ( GVW ) would determine which axle housing many cars and trucks received.(*Note-See New bearing information under Housing Section Below-updated 12/04)
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:Some 1/2 ton Vans and Trucks used the 9 inch right up until about 1985/86 or so in limited quantities*), and with many 1973 to 1979 pickups to still be found on the road and in junk yards,these are very plentiful. And since the “Limited slip” or Locking rear end (often referred to as a “POSI”) came to be a popular option 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.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 case I see frequently is the C7AW-E, it is the one commonly found in the trucks,vans and cars throughout the late 60's and the 1970's, right up until around 1985 in some truck applications. 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 they 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 butt welded carrier centers to tubes and a smooth backside. Later housings appeared in 1966 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 (have heard it referred to as the "Banjo style"). In general 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 - this will also be the narrowest stock Ford 9" application (about 52" housing flange to flange).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-(mainly GT's in 68 with optional gear ratios)* and 56” for the 1971 to 1973 Mustangs/Cougars- (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.

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”(the C7AW-G mainly) 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.Have heard that the case C4AW-4025-C is also a large bearing single ribbed 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's a quick tip someone sent me for spotting an N case while installed in a housing, look to the area just to the right of the carrier fill plug on side of case, on an "N" case an only an "N" case this area will be filled in-flat cast metal. On the "WAR", "WAB" and standard cases there will always be a cast in recession that forms a pocket. The 9 3/8" also has this area filled in-but it has the bent down horizontal rib end.Compare the various photos on page and you should see what I am talking about.
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

Photo below shows a the D2OW-C hooded daytona pinion support which may have been the last Ford production Daytona support from what I have seen.

Photo courtesy of Shawn Reim

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).

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.

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.

(above)Small bearing shaft on left, large bearing shaft on right


Note the early axle shaft with tapered middle section, these cannot be shortened or resplined

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 and in format of Wxx-x etc. (these can be referenced in id manuals to identify original car/truck type installed in), the gear ratio and date code are given as well- with the gear ratio generally starting the second line followed by the date code (most of the time). If the unit is a locking type, the gear ratio will have an "L" after the first digit and before the final two digits (else there will be a blank space for an open). The final info given on later tags is the housing type installed into (which can be used to identify car/truck line installed in as well) - ie. an 8 inch Mustang, 9 inch Mustang, 8 inch Fairlane etc., housings can be slightly different even for similar or the same models. For instance, an 8 inch Mustang houlsing (67-70) is "930" while an 8 inch Cougar for the same years is a "931".The slight difference probably due to the different style lower spring plate and larger center pin hole used on the Cougar housings with the rubber pads - similar to the Fairlane mounting set up, while the Mustang housing has a smaller center pin hole in spring perch. This final axle Id number can also be found on a cars build sheet (67 on up), just look under "Axle" section, it will appear slightly different, with the a single digit at start that stands for model year folled by the three digit axle housing Id number and then a letter suffix (this suffix will sometimes appear on tag line as well). Thus an 8 inch housing used in a 68 Mustang would have "8930A" in the box labeled "Axle" on its build sheet, and most likely just the "930" or "930A" on axle tag itself.A similar build sheet for a 67 Mustang with an 8 inch housing would have "7930A" etc..Axle housing id numbers I have are the following: 831- 68/69 Fairlane/Comet/Cyclone/Torino 8 inch, 868 -68/69 Fairlane/Comet/Cyclone/Torino 9 inch, 903- 67 to 69 Mustang 7 1/4 inch, 913- 65/66 Mustang 8 inch, 930- 67 to 69 Mustang 8 inch, 931- 67 to 69 Cougar 8 inch, 996- 67 to 69 Mustang 9 inch. 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:



Above is the earliest style tag I have seen used (mainly on 57/58 Fords), it is quite simple - just the ratio given, here 3.56.



Another 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.

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.

The traction loc

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 complete,but it is put together out of my experiences (with the help of some personal friends and internet member contributions) in searching out Ford rear ends over the last few years .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.