REAR DIF Identification

[wescfe]

I found a rear end (differential) out of a '74 F-100.
It has a tag, but it's old and rusty.
I request opinion and help with the ID.
I'll attach the picture - here's my interpretation:
WB ? - AC 3LB
? 5 - 9 331A

I can't find a code similar in an the early '70's year range
thanks,

[fastEdsel]

My guess is it's a Ford 9 inch, 3:31-1 ratio. Poor man's way to try it is to jack up the rear axle off the ground so the wheels spin freely, place a mark on the pinion dust cover, rotate the wheels and see if you get approximately 3 1/3 turns of the pinion to every single rotation of the wheel. Then it's most likely a 3:31 ratio. The only other way is to pull the differential out and read the stamp on the crown gear. Good luck, let us know.

[basketcase0302]

"wescfe"]I found a rear end (differential) out of a '74 F-100.
It has a tag, but it's old and rusty.
I request opinion and help with the ID.
I'll attach the picture - here's my interpretation:
WB ? - AC 3LB
? 5 - 9 331A

I can't find a code similar in an the early '70's year range
thanks,

Stop by the welcome mat when you get a chance:
http://www.fordification.com/forum/viewforum.php?f=1

What FastEdsel said above will get you close and here's the axle code sheet:

http://www.fordification.com/tech/dana-rear-01.htm

[ultraranger]

Hard to tell for sure from the photo and the amount of crustiness on the tag but, It looks like it reads: WDM-AC

If this is the case, the 3rd member has a 3.25:1 ratio, open (single track) 28-spline differential. "3LB" indicates the 3rd member was assembled the 2nd week of November, 1973.

[wescfe]

I think UltraRanger is correct - it's the only thing that makes sense.
Thanks everyone for the help.