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

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 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)


Shown above is an example of an Equa lock 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.

Shown above are the internals of a four pin Equa lock differential. Note the five “fingers” on the steel clutch plates (the tiny circular tabs on outer edge) Trac lock units will have only 4.


Here is a close up of a Traction Lock, note recessed bolt holes through cover for holding ring gear on. The bolt head is 5/8 and uses a thin washer.



Shown is a 28 spline open differential. Notice the flat surface around bolt holes. Bolt head would be 3/4", no washer.

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.
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. 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

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