Had the opportunity to pick up another Ford 9" rear end on the weekend which I think will be more appropriate to my needs. Am having some difficulty decoding the axle tag however. PO says it is from a 1971 F100 and the date code on the tag seems to support this, but I can't find a reference for the axle code WDM ADD - closest I can find is a WDM AD.

The full tag reads:
WDM ADD 1F30
3 25 9 S311B

I'm pretty sure from the tag it is a 3.25 ratio, 9", with a build date of 1971/Jun/30. Don't know if it is 28 or 31 spline.

The only table I found was on FORDification and does not list a WDM ADD.
Ford Rear Axle Assembly Identification - Page 03 - FORDification.com

My objective is to know where it came from for sure so I can order the proper new brake components. I can see that it had 2.5 inch brake pads but I don't know what size bore the wheel cylinder should be - there seems to be a wide choice from 7/8 all the way up to 1 3/16.

 

It doesn't have existing wheel cylinders? I have a '70 9" out of an F-100, also a WDM, these are the brake parts I used (also 2.5"):

Rear axle seal NAPA 15142
Rear wheel bearings NAPA 88128R
Backing plate gasket NAPA 55036
Brake hardware kit: NAPA 2241
Left wheel cylinder NAPA 17507
Right wheel cylinder NAPA 17508

 

Thanks for the quick reply ALBUQ F-1.

No it came with the backplate, drums & shoes only - thus my question.

In my research I saw the NAPA cylinders you mentioned. These are also Dorman part numbers and are listed as 7/8" bore and for the 1/2 ton series. What is causing me concern is that NAPA also shows UP36057/8 and UP18290/1 and these are 1 1/8" bore which I thought might be appropriate since the shoes are the almost largest possible at 2 1/2".

I obviously have a lot to learn.

 

Kevinstang's Ford Nine Inch Differential Page + Try this Steve.