Hey guys, I have a 2011 with 3.73 rear end. I am going to go abead and flush out the factory stuff, and check for metal shavings. Advance Auto Parts has killer deal on Royal Purple 75w-140 and i bought 3 qts. My question is, do i need yo add the 4 oz of friction modifier or just assume the RP has enough in it?

Thanks,
Ryan

 

... This is one of those things I don't understand.... If the factory fluid has no issues, why change it??? If it ain't broke don't fix it right???

 

If the fluid is specifically for limited slip type diffs then no you won't need any. If it's just a general gear lube then I would suggest a friction modifier of some sort. Personally I would only go with a gear lube that is specified for ls diffs.

 

I saw on another fourm a flush where a lot of metal shavings came out. Its its a $35 precaution. So i am doing it. No need to try to talk me out of it haha.

The royal purple is for LS differentials, but what i really mean is, how much friction modifier is too much?

 

The RP oil is supposed to have the friction modifier already in it. I have heard that it may not have enough to match Ford's recommended amount. If you do the oil swap and notice any chatter from the diff afterward then you may need to add more modifier.

 

Driving it without and actually experiencing chatter wont damage it?

 

If you use the RP it won't be without but it may not have quite enough.

Won't hurt to drive it that way for a short time, it would only chatter going around corners or tight turns.

And it's not for sure that the RP won't have enough friction modifier, just might not.

 

I see. Thank you. I am going to go ahead and buy some from ford because you are supposed to put it in first. Maybe just a splash. Then see what happens from then on out. I will take some pictures and see what I find.

 

You don't want to put in too much, just as bad as too little, maybe worse.

Too much and the clutches won't grab and you lose the limited slip.

 

Crap. Let me go look at the bottle of RP and see exactly what it says.

 

Don't get any of that friction modifier on you, it smells bad.

 

I didn't want to take a chance. I used the factory synthetic Motorcraft and 4oz of friction modifier. I changed mine at around 7,000 miles. The old fluid was very dark and the magnetic fill plug had a lot of fine metal stuck to it.

 

i changed the diff. fluid in my 2003 GT, used Mobil1 synthetic 75w-140
Mobil1 states it has FM in but you can add if you want to
i ended up putting in 2 oz. - didn't want too much slip

the LS started going south with a groan or grating noise on slow turns, like when you do a 180 and back into a spot, it then turned into a full chatter or clacking

after about 500 miles all the noises is went away

the fill is 2 quarts + 4 oz. FM

 

The royal purple bottle says proudly on the front *For Limited Slip Differentials, as well as Posi.

I might just filler up and see what happens. I am a strong believer that RP>Motorcraft as far as quality goes..

 

Also, I think the factory fill is 5.3 Pints = 2.65 Quarts. So about 2 and 3/4 bottles.

 

why do you think royal purple is better? because it cost so much and has a catchy name? do you think fram filters are better than motorcraft? do you actually know the oils composition and additives?

 

If you're going to pull the cover.... I recommend the Boss cover which has fins on the outside AND the inside. Much better cooling. Plus you might consider drilling and tapping the cover for plugs to facilitate oil changes in the future.

 

Good post

 

Yeah, i enjoy wasting money. All oil is the same right? Actually, Wal Mart oil is the best beause its in a cool blue bottle and it says "super" on it. Really makes me sleep better at night

How about you quit drilling me on my decision to flush the dif. I am stimulating the economy! Haha

Royal purple is better, there is no question about it.

 

Get three quarts. My V-6 rear end held around 2 and 1/3rd quarts after adding the 4 oz of friction modifier.