I will be replacing my differential fluids this weekend. What kind of fluids do I require and how much quantity for Dana 80 rear and Dana 60 front. Most importantly, does it need friction modifier?

 

Also, the procedure is to open all cover bolts, drain & clean up. After that put in new gasket and in my case new chrome cover, right? Then pour fresh oil through plug hole, correct?

 

What oil are you using? The reason I ask is that some oils, such as Royal Purple synthetic 75w-140, what is recommended for the rear diff, already have the friction modifier in them. I also believe you can use the same oil in the front differential, though the owners manual specs 75w-90.

OOPS, just re read your signature and see that it IS a dually. DOH!!!


Capacities: Front-5.8 Pints(2.9Quarts) Rear-8.5 Pints(4.25 Quarts)

Procedure sound right, just leave 1 or 2 bolts(loose) on the top of the cover so it doesn't fall off and get oil everywhere. As far as I know, silicon is used instead of a gasket.

 

Here are the pics I took when I did my Sterling. Your procedure is about right, but did you get a gasket? My stocker uses just some gray Permatex, no gasket.

Now sticky part. I've been told there is a TSB about the front & rear diffs changing the fluid weights from 75w-90 to 75w-140. I did a quick search, but didn't find it. You might get with your Ford dealer and see what they recommend. I have a 2wd with a LS Sterling -- I know it takes 75w-140 with friction modifier. I'm sure your rear diff takes it, but don't know about the front. Either way, don't add too much. Add just enough to keep the rear from chattering on tight turns. Some folks think friction modifier makes the clutches stick, it's actually the opposite! The more modifier you add, the more they slip. So that's why you want just enough to keep them from chattering.

EDIT: This is from the manual. He has a dually, Mike. Dana 80. Not sure when they switched the front from a Dana 50 to 60, but I think the 2000 has the Dana 60.

 

If its a limited slip diff then you'll need the friction modifier. If its open you won't.

I run Red Line oil in my diff. It already has the friction modifier in it....

 

Thanks, I'm 100 % sure mine came from factory with Dana 80 rear( mine is dually) and my front is Dana 60. All 1999-2003/4 dullies came that way.

 

I just re read your signature and edited my post to reflect that.

 

ok, few more questions, I thought all Lariats came as limited slip. Also, I do need to use the sealant when I use the new gasket, right?
Here is what I have:
#1 two new diff chrome covers and bolts
#2 two gaskets.
#3 Sealant--Do I need this?

 

Thanks, I saw the new edit...

 

Did you use any sealant when you put in the new gasket? I'm sorry, I have never done this before and I don't want to pay Jiffy lube any more...

 

I don't know if the Dana 80 requires a gasket or silicone, or both. Maybe someone that has had their hands in a Dana 80 will stop by...

I'm pretty sure the Dana 80 is LS, and if the fluid you buy doesn't say it has friction modifier, you need to add some. Put in 2 ounces and test drive it. Make several tight right & left turns. If you hear a chatter in the diff, add another ounce and repeat the test.

I'm not sure how the front diff works, and if you need friction modifier or not in it. My wife's truck is the first 4wd we've owned, and it only has 16k on it. Haven't had to tear into it too much.

 

Your front axle is a Dana 60. I just had mine completely apart. Puke the diff by removing all of the bolts and pry the diff cover off over an oil pan.Clean up the mating surfaces and try not to get any crap in your gears. You don't need a gasket, just use RTF. I used alcohol to ensure a nice clean surface to apply the RTF bead and bolted it up by torquing the bolts to 35lbs-ft. There's an allen head bolt closest to the spring u-bolt. It's an 8mm allen head. That bolt has to go back in that spot. Don't add fluid until an hour passes after you torque the bolts and let the RTF set.

On my SRW CCLB F350 w/ 3.73's, I used Valvoline fully synthetic 75W-140 that already has a friction modifier in the front and rear axles. The rear axle has LS. I drove it around and had to add even more friction modifier so it would stop shuddering around tight corner take-offs. I bought the friction modifier at my local Ford dealership.

 

Well, when I replaced my fluid, I also installed a Mag Hytec diff cover that has an o-ring built in for the seal. But I believe the normal way is to just use a silicone bead to seal.

 

Ok, two questions, what is RTF?
second, Are you talking about the allen head on the diff cover itself?

 

I'm all confused now. I called a local dealer and he says, if it is LS differential( mine is) it does not need friction modifier!!!! And if it is locking differential it needs friction modifiers.
So, what is locking diff? I always thought Limited slip needs friction modifiers.