I've a 72 F100 short wheel base and i'm wanting to know what the numbers on the tag that is attached to 9" ford rear. The tag has WDN-S 9MA
3 25 9 313A

 

The 3 25 means 3.25:1 ratio. with the 9 being Ford 9". Don't know what the 313A stand for.

 

SCWalt this site can give you something to read up on. Kevinstang's Ford Nine Inch Differential Page +


John

 

Look at that tag number again, there is no such number of WDN-S listed in any 1957/87 Ford car or truck parts catalog.

It should read WDM-S

WDM-S = Ford 9" / 3.25-1 / Non Limited Slip / Large wheel bearings / Large differential bearings / 28 spline axle shafts / Used before serial number J30,001.

Why is the axle ID tag and serial number important?

After J30,001, Ford went to "Slim Line" differential bearings, and changed the case.

Your truck uses B7A-4616-B diff brg cups (Industry # LM603011) and B7A-4621-B diff bearings (Industry # LM603049)

These are the largest 9" diff bearings used. Besides the "Slim Line," there were medium sized bearings also used.

Sorry to be so technical, but when Ford changed the *&^$ case and bearings, it was a PITA, because most ppl and autoparts stores back then didn't know the difference, and sold the wrong parts, and still do today.

btw: Some ppl here think I list too much info, but too much info is better than no info, or wrong info!

 

Don't listen to "those ppl" numberdummy...I like to much info, you seem very informed and the knowledge is appreciated!