Ok, here is one for you. My 2004 F-150 door tag says we have a B5 or limited slip 4.10 ratio differential. Good enough but as I have the 163 inch wheel base Heavy Duty my question is what size is the diff? It is a 12 bolt. I have been unable to find out what the code tag means that is under one of the bolts.

Tag reads: L101023F18 on second line: 3V121F

Also on the right side axel tube is a sticker that has the number V121F on it.

I ordered a Mag-Hytec cover, FORD-F 12-9.75 and it is too small to fit. It is 12 bolt but is short side to side. My cover original looks like it might be a 10.25.
Does not make sense to me at all. This is a very early production 2004 5.4L, 3V.

HELP?

 

Maybe the L101023F18 could possible be partially decoded as:

Limited Slip 4.10 ratio 10.25"

The rest is a guess.
Maybe we got lucky and got the bigger differential, a 10.25 instead of a 9.75?

 

7 lug wheels? That's a 10.25.

 

Yes, 7 lug wheels! That is where I was going....Thanks for the input glc!

 

heavy duty means 10.25 sterling

 

You guys are very helpful.

Larry