Is there any way to know if I have 28 or 31 spline axles, Short of pulling them out of the houseing? I have a 1976 F150 Custom with a 360. The tag says it is a 3:1 open diff. I don't think the tag has a code for the axles, does it?

 

Get me all the letters/numbers off the tag and post them as they are on the tag.

 

Here it is:
WDM-BC 5HB
3 00 9 386D

Thanks.

 

All trucks, 67-up are 31 spline, and have the toughest housing available.

 

I think F100s had 28 spline and F150s had 31 spline.
I'm sure I counted 28 when i had the shafts out of my 1979 F100.

 

lemme go look....


Everything you've ever wanted to know
about Ford 9 Inch Differentials!



Research and photography by KEVINSTANG66 @ aol.com
http://www.geocities.com/kevinstang66/

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.




Exploded View
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, 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 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.

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:

How to identify Open vs. Equa Lock vs. Traction Lock
The two basic types of “posi” units are the early Equa lock and the subsequent Traction lock units. I am not exactly sure when the Equa-locks 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 types and most parts do not interchange.

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)

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. If you have any information to add, email us at editor @ fordmuscle.com.

Special thanks for Kevinstang66 @ aol.com for documenting this extensive compilation of Ford 9-inch information. F/M

 

yes, 28 spline axles were used up until 1979 and are usually but not always found in F100's 31 spline axles were used usually used in F150's but again not 100% of the time. there are actually two different types of equalocks and the first design came out in 57 and my 59 tbird has one. the equalock was discontinued in early 1970 production but was only used in limited applications in 68-70. the trac loc came out in 68 and was used in all performance applications. the trac loc was redesigned in 1970 to eliminate a weak spot in the case design that caused broken side covers. hawkrod

 

My 77 F-100 came with 31 splines but it also had the 5 leaf spring pack in the rear.