Hey guys, 

My dad has an 03 2500 ext cab lb with a hemi, yuck! lol anyway, he was asking me if I knew anything about what fluid he needs for his diffs. I only know what I read over on CF and that is that it should have an AAM axle with gear driven limited slip, if it even is limited slip, and so should not need any LS additive. He said he could find any identifying info on the axle sonintold him to ask the dealer. He did and they told him his truck does have a LS rear and that he does need fluid with LS additive. Does that sound right? I though all 3rd gens have AAM axles which have gear driven LS and so don't need the additive? They didn't tell home what axle he has. He said they didn't seem too knowledgeable. Can someone set me straight here? 

 

Also, do you have to be careful with running the exact same tires with a gear driven LS like you do on the 2nd gens? 

 

And can you safely run two different tires on the front axle of a 3rd gen? 

 

Thanks guys!

Any help is much appreciated and I trust you all way more than I trust CF or the dealer lol.

No clutches in the LS units in an AAM so no need for ls additive, as far as running 2 different size tires.......................WHY??

as long as they are close it would be no issue as the LS unit in an aam is a different animal than a clutch type all together and is more forgiving in that regard.

1 minute ago, Wild and Free said:

No clutches in the LS units in an AAM so no need for ls additive, as far as running 2 different size tires.......................WHY??

as long as they are close it would be no issue as the LS unit in an aam is a different animal than a clutch type all together and is more forgiving in that regard.

Sorry I should have clarified, not different size, just different brand/tread. Is it certain that his 03 Hemi will have an AAM, or could it be a Dana and that's why the stealership told him it needs LS? Also, is it safe to run different tread patterns on the front axle as well?

Thanks for the reply btw!!

^^^^ This

How does the gear driven LS work anyway?

 

Thanks for the education there Bill. That was interesting.

Yes thank you! That is very informative!

Is it certain that an 03 hemi would have this? Or might it still have a Dana? 

 

Now what about the front axle in a 4x4 3rd gen? How does it work? Is it tied together all the time or is it open like a 2nd gen? 

My 02 has a tag in the glove box the lists both the front and rear diffs that came on the truck. Maybe the 03 does also.

3rd gens only have AAM axles as far as I know ford is the only company that went back to Dana after they released a heavier axle than the 80 several years back but have not kept up so not sure what they run now.

 

As far as the front axle it is full live just like the late 01 and 02 2nd gen Danas meaning there is no central axle disconnect., drive lines and axles all spin all the time. This is why free spin hub kits are more popular with 3rd gen guys.

As W&F mentioned all 3rd gen and up trucks use AAM. AAM only has a helical gear LSD so no additive needed. 

 

It's still a LSD so different tires can be run but better to stick with same brand, but no worse than a new tread and a used tread on the same axle. 

7 hours ago, leathermaneod said:

Yes thank you! That is very informative!

Is it certain that an 03 hemi would have this? Or might it still have a Dana? 

 

Now what about the front axle in a 4x4 3rd gen? How does it work? Is it tied together all the time or is it open like a 2nd gen? 

I had an 03' hemi 2500 aam axles. I used amsoil 75-90 with no issues.