Hey guys and gals,

I did my truck a favor today and replaced my rear differential case fluid.

I take it that the old fluid being dark gray and nasty looking needed changing since its the original 10yr old fluid!

I used Valvoline 75W90 100% synthetic and let me tell you, I noticed a huge difference in how the truck rides/coasts/takes corners. Definetly needed to be changed!

Is there anything special I need to watch for in the next coming days?

I sealed the cover to the case with RTV high temp gasket maker silicone, no leaks since about 1:00pm today. I made sure the case was dry and tried to soak up the old fluid that dribbled on it during the emptying, so I could look for any leaks in the morning.

Cheers!

 

Sounds like everything should be good. You're sure you don't have a limited slip differential right?

 

Uhm, if its an option thats not standard then I probably don't have it unless my grandfather ordered it on the truck....Is there a way to tell? I remember how all the gears looked arranged....is it in my VIN decode?

 

You can check your door sticker against axle code charts here:

http://www.ford-trucks.com/article/i...de_Chart_.html

and here:

http://www.ford-trucks.com/forums/11...xle-codes.html

 

I do not know if your truck requires it but my 2005 4x4 S.crew requires 4 oz. of "slip-lok" to prevent "chatter" from the rear differential, unless you use a gear lube that already has it blended in.

Royal Purple claims to have the modifier already blended in so no need for the additional 4 oz of friction modifier.

I recently watched a friend change his rear differential after (I think) about 50 thousand miles on it and it was black/gray, smelled bad, and had visible wear debris in it. But he tows a lot of equipment 6 days a week.

 

The Ford limited slip additive makes your fluid grey and smell bad as well so it is not a good indicator of condition.

 

Well my fluid was grey/black and had a watery look to it. I'll have to look into this to see what type of diff. I have.

Found it:

H9 — 3.55 limited slip (F-150

THat means its good? lol I don't know anything about gears.

That means I NEED or SHOULD have the additive? No chatter yet, ts running smoother than before......

 

If you have the limited slip the you DO NEED the additive

 

Yes you need the additive. You will start to chatter once the clutch plates are washed clean with the new fluid. Drive some tight figure 8s in a parking lot after you add the friction modifier. This helps get it into the plates.

 

add 4 oz modifyer!!

 

OK so I go to my ford dealership or can this stuff be purchased at NAPA?

 

I'm not sure if napa carries it?
I got mine at the dealer

 

Just get it from the dealer. You can get it from auto part stores, but if you get it from the dealer you know you're getting exactly what was made for your truck.

 

Alright guys, thank you, just ask for Differential limited slip additive??? Is it terribly expensive?

 

Should be under $10