2004 f250 axles and oil?

[emilio]

Can I use the royal purple syn axle oil in both front and rear. Just bought new diff cover for both axles and will be replacing them this weekend. what gear oils do you guys like.

[astroinhouston]

I put Amsoil in the front and rear back in January and have been very pleased with it.

[bfrank81]

Originally Posted by astroinhouston

I put Amsoil in the front and rear back in January and have been very pleased with it.

x2 I added the Motorcraft friction modifier just to be safe.

[NYC F-350]

Originally Posted by bfrank81

x2 I added the Motorcraft friction modifier just to be safe.

Bad idea if the Amsoil has the modifier in it already. What adding more to it will do is make the clutches in the limited slip...slip when you need it most.
The best way to figure out just how much you really need is to not add any at all. Drive the truck a hundred miles or so, and if you feel chatter (if you need modifier, you will know it when/if it happens) pour 3 or 4 ounces of the modifier in through the hole of the VSS (or rear ABS sensor). Then repeat the test. If it still chatters add 1 or 2 ounces. You want to find the perfect balance of modifier. Too much and the limited slip won't work, not enough and you get chatter.

[bfrank81]

Originally Posted by NYC F-350

Bad idea if the Amsoil has the modifier in it already. What adding more to it will do is make the clutches in the limited slip...slip when you need it most.
The best way to figure out just how much you really need is to not add any at all. Drive the truck a hundred miles or so, and if you feel chatter (if you need modifier, you will know it when/if it happens) pour 3 or 4 ounces of the modifier in through the hole of the VSS (or rear ABS sensor). Then repeat the test. If it still chatters add 1 or 2 ounces. You want to find the perfect balance of modifier. Too much and the limited slip won't work, not enough and you get chatter.

Take a look at this.

Add 8 oz. (236 ml) of Additive Friction Modifier XL-3 or
equivalent formulated to meet Ford Spec EST-M2C118-A
for complete refill of limited slip axles.

If they are recommending that you add 8 oz I added 8 oz.

[NYC F-350]

I'm just telling you how to get the best performance out of your limited slip. You can do what you want. I have 0 friction modifier in my rear diff.

[NYC F-350]

Also, keep in mind that "they" write those to give you a general idea. A rear diff with 50,000 miles on it will need a different amount of modifier than one with 100,000, and that one will need a different amount than one with 200,000 miles on it.

And if your going by what FORD says, you shouldn't be changing your rear diff fluid anyway. They say it is a "lifetime" fluid.

[bfrank81]

When this service is done by the dealer how much do they add?

[NYC F-350]

Enough to keep the customer from returning. You think they give a crap if you get stuck on your front lawn?
It is actually in FORD's best interest for your limited slip to not work properly. Then when you go in and say that you got stuck on your slight slope of a lawn, they tell you "all you need to do is rebuild the clutch pack" CHA-CHING, thank you. Have a nice day
Go on the 4X4 boards and ask them what they do.....

[bfrank81]

Ohh well it's done now. I'm not dumping all that $$$ fluid out and refilling it.