Third Member Cases

FORD 9-INCH THIRD MEMBER CASES

The Ford 9-inch third member cases came in three different casting configurations between 1957 and 1965.
 
GRAY-IRON THIRD MEMBER CASE:
 
The first style of Ford third member produced was the "WAA", "WAB", or "WAR" cases from 1957-1960. These are the "gray-metal" cast-iron units and are the weakest of all the 9-inch third member styles.  The gray-iron units have two vertical ribs and four horizontal ribs across the face of the casting. The horizontal ribs will have a continuous arc to their shape. There will also be depressions in the casting in between the horizontal ribs, near the outer bolt circle.  The casting letters "WAA", "WAB", & "WAR" can be seen on the inside of the third member next to the right-hand differential bearing stand.

 
 
The weakest style of Ford 9-inch third member produced from 1957 - 1960. Notice the "WAR" casting letters. 

FIRST THIRD MEMBER CASE REVISION:

The next version of the Ford 9-inch third member came around 1960. This is the most commonly seen style of Ford 9-inch third member case and can be identified by its single vertical rib and three horizontal ribs. This style was produced from 1960-1980 in the Ford passenger cars and from 1960-1985 in the Ford half-ton pickups. This third member is cast with a fair amount of nodular iron which gives it greater strength over the weaker gray-iron units.
 
 
The most common style of Ford 9-inch third member. Notice the "C1AW" casting number.

N-CASE THIRD MEMBER:

The next revision to the 9-inch third member came in 1965. This revision was known as the N-case. It had a high nodular-iron content that allowed the case to flex instead of shatter, like the older gray-iron units were notorious for (as in drag racing situations). This third member looks very much like the gray-iron third members at first glance, but there are some very distinct differences.

The horizontal ribs are not continous in their arc, but rather have a "flattened" out appearence at the extreme ends. The area between the horizontal ribs is also flush with the surface of the casting (no depressions present). Most N-cases will have pinion housings that are approximately 3/8ths of an inch thick and will have a level surface on the face where the five pinion housing bolts pass through. (Notice I said "MOST", since here is an N-case example with the raised-bosses around the pinion housing bolts like the pinion housings most commonly seen on the other types of 9-inch third members).

The first N-cases were produced from 1965-1969. These didn't have an "N" casting on the face of the third member between the two vertical ribs like the later versions did. The physical differences in appearance is the only outwardly way to tell them apart from the earlier gray-iron units. These units have the Large differential side bearings and can be identified by looking at the casting number inside the case next to the right-hand differential bearing stand. The only casting number for this style N-case is "C4AW-B".

The next revision to the N-case came in 1970. These revised N-cases came with the more fimiliar "N" cast on the face between the two vertical ribs. These N-cases have Meduim differential bearings instead of the Large differential bearings like the '65-'69 N-cases. The casting numbers to identify these '70 and up N-cases can also be found inside the third member, next to the right-hand differential bearing stand. They should read either "D0OW-B" or "D0OZ-B". The N-cases are the ultimate Ford 9-inch third members for strength. I'm not sure if the N-cases were produced all the way through 1985, but I do know that they were being produced at least as late as 1976.
 
 
Notice "D0OW-B" casting next to right hand differential bearing stand, this casting number is for an N-case! Also notice the "N" casting on the other side of the right bearing stand.


Another "D0OW-B" casting! This is another N-case!

Example of the 1957 - 1960 WAA, WAB, WAR third member casting. Notice "depressions" between the horizontal ribs near the outer bolt circle. Also, note the "DIF" casting on the passenger's side of the case. This doesn't stand for "Differential". It is the markings for where this case was cast: "Detroit Iron Foundry." Most common style of Ford 9-inch third member. Notice single vertical rib & three horizontal ribs.


The N-case on the left has the more common thick pinion support, while the N-case to the right has the less common (for N-cases) pinion support with raised bosses in the pinion support bolt area.


 
Differences between the 1957 - 1960 WAA, WAB & WAR case vs. the N-case (N-case to the right). Notice the lack of depressions on the N-case. Also notice how the N-case´s horizontal ribs flatten out at the ends.


Conventional third member to the left, traction lok third member to the right. Notice the large ring gear bolt heads on third member at left, while ring gear bolt heads are much smaller and also shrouded by the differential case on the right-hand third member. The ring gear bolts on the left requires a 3/4" socket to break them loose, while the ring gear bolts on the right-hand third member requires a 5/8 socket.


 
Thickness of ring gears & and ring gear tooth spacing can give you a good idea (at a glance) if the third member has a high or low gear ratio. The "thin" ring gear w/ close tooth spacing indi cates high ratio. "Thick" ring gear w/ teeth fur ther apart indicates low ratio. Third member on left: 3.00:1 ratio. Third member in middle: 3.50:1 ratio. Third member on right: 3.89:1 ratio .


A LIST OF SOME OF THE FORD 9-INCH THIRD MEMBER CASES PRODUCED FOR THE HALF-TON PICKUPS:

1960-1972

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of: WBG, WDM, WDN, WDR, WEW, & WFF:

1. C0AZ 4141-C (Medium Differential Bearing)

2. C1AW 4141-C (Medium Differential Bearing)

3. C2AZ 4141-B (Extra Large Differential Bearing)

4. C6AZ 4141-B (Extra Large Differential Bearing)

5. D0OZ 4141-B (Slim Line Differential Bearings)

6. D0TZ 4141-A (9 3/8" case, Extra Large Differential Bearings)


1960-1972

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of WCR, WDF & WEV:

1. C0AZ 4141-C (Small Differential Bearings)

2. C2AZ 4141-B (Large Differential Bearings)

3. D0OZ 4141-A (Slim Line Differential Bearings)


1960-1972

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of WFE :

1. D0OZ 4141-A (No further information)


1960-1972

Ford half-ton truck 9 3/8-inch third member cases produced under the Tag I.D. prefix of WFF:

1. D0TZ 4141-A (Extra Large Differential Bearings)


1973-1979

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of WDM:

1. C7AW 4141-E (No further information)

2. D0OW 4141-B (N-case, Conventional differential)

3. D0OZ 4141-B (1973-1976, N-case, Daytona Axles)

4. D7AZ 4141-A (1973-Up, Non-Daytona Axles, 2.75-3.70 Ratio)

5. D7AZ 4141-A (1973-Up, Non-Daytona Axles, 4.11 Ratio)


1973-1979

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of WDM & WEW:

1. D7AZ 4141-A (1973-Up, 2.75-3.70 Ratio)

2. D7TZ 4141-A (1973-Up, 4.11 Ratio).


1973-1979

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of WEV:

1. D7AZ 4141-A (1973-Up, 2.75- 3.70 Ratio).

2. D7TZ 4141-A (1973-Up, 4.11 Ratio)


1973-1979

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of WFE:

1. D7AZ 4141-A (2.75-3.70 Ratio)

2. D0OZ 4141-B (1973-1976, Daytona Axles)

3. D7AZ 4141-A (1973-Up, Non-Daytona Axles, 2.75-3.70 Ratio)

4. D7TZ 4141-A (1973-Up, Non-Daytona Axles, 4.11 Ratio)


1973-1979

Ford half-ton truck 9-inch third member cases produced under the Tag I.D. prefix of WFT:

1. D7AZ 4141-A (1973-Up, 2.75-3.50 Ratio)