Just recently took a look at my rear diff tag:
V 905 A
L73 9 75 2E29

My axle code is B6: 3.73:1 LS

After looking on some other Ford forums, the "L73" seems to mean 3.73:1 LS and the "9 75" indicates the rear differential size.

I have the 4.6L engine, but the axle tag seems to indicate a 9.75" rear. Was this an option? I always though the 9.75" rear only came with the 5.4L engine option.

 

Usually, it is the 9.75 and 5.4 combo. Also, I don't remember seeing a 4.6/FX4 combo before. It always seems to be the 5.4. Possible someone dropped a 4.6 in?

 

You might have gotten lucky and gotten the bigger axle. That to me seems more probable than a 4.6 being dropped in.

 

I bought the truck in 2005 with only 15,000 miles on it. It literally looked brand new (except for the *****ty factory goodyear ATS tires, haha), so I'm pretty sure the 4.6L is original. I looked in my Haynes manual, and it mentions the axle tag having the diff size on it. Don't see a "8 8" anywhere like I expected.

But from what I understand, the 3.73:1 LS was only an option for the 5.4L then. I'm guessing they decided to put bigger/lower gears since the dude that originally bought the truck skimped on the engine option. But the deal was too good to turn down at the time in spite of the 4.6L!

 

are you absolutely positive you have a 4.6L? I'm pretty sure the FX4 package came with the 5.4 standard.

maybe the previous owner just wanted the 4.6 and got the rest of the FX4 options.

 

Yeah man, the that plastic part that covers the throttle body says 4.6L. And it sure doesn't run like a 5.4L ! haha

But you're right, that's probably what happened. The original owner probably ordered the 4.6L thinking it would get better gas mileage, lol.

Edit: Just checked the VIN, definitely 4.6L is the original engine.

 

Also, count the bolts on the diff. 10 = 8.8, 12 = 9.75. Another possiblity is that the the rear was replaced.

 

Yep, I counted 12. There's no way the rear end was replaced before 15,000 miles.

 

Thanks for the informative posts. This one I was searching for.. I got some idea. I will comeback with what I have done.

 

Here's one for you:

I had to replace both axle bearings because they wore out and wore grooves in the axles. I called ford with the VIN and they said I had a 9.75". I have a 99 f150 5.4. They said they switched from 8.8 to 9.75 about half way through production. Then I found the tag on the rear end. It also said 9.75. I went out and got both repair bearing for a 9.75. Took the whole thing apart and it was 8.8. Either someone replaced the entire rear end before I got the truck or the factory screwed up on tracking which was which. I think it must have been a factory mistake cuz it was documented as 9.75 and even had the tag for 9.75.

What do you think?

Just a note cuz this is really confusing to me. I just went out to count the bolts. I have 12. They say 12=9.75. Everything points to 9.75. However I got parts on 2 seperate occasions. After the first time I forgot the size and just got bearings for both. The one for the 9.75 is WAY too big to fit in the axle housing (not sure housing is the correct term). How is this possible? You have the rear end and then the axle housings coming off each side. They are probable 3-4" diameter and a few inches before the wheel, they taper down about an inch. There is no way the bearing for the 9.75 would ever fit in there. The 8.8 fits perfectly. Anyone know whats going on? Wondering if something was replaced with the wrong part.

I would appreciate any help