Friction Modifier Not Required?

[DsrtExplorer]

I am working my way thru a new to me 1991 Ex and changing out the fluids and when I came to the rear differential I found a thread that mentions the 3.73 LS rear ends need 75W140 synthetic based on a TSB. While shopping for the right fluid, I came across Valvoline 75W140 full synthetic that states on its website "no need for Ford M2C118A friction modifier". Is says that it is in the gear oil itself. Is anyone running the Valvoline full syn and leaving out the friction modifier without problems? Thanks for any advice.

91 XLT

 

[biff9703]

I have used it with no problems on 2 ls diffs with no problems. A 96 and a 97 5.0 Ex.

 

[swshawaii]

I've heard both when people have used aftermarket diffy fluids that contained FM such as Castrol, RP, Valvoline, etc. Guess the only way of finding out is turning and seeing if you get "chatter". If it were me, I would add a $5 four ounce bottle of Motorcraft XL-3 FM additive, and be done with it for the next 30K or more. In other words, it can't hurt.

 

[arco777]

I used that Valvoline in my Mustang with a LSD 8.8, and the diff didn't really like it. Had to add friction modifier which improved the chatter, but it still makes noise that it didn't use to with the old fluid.

 

[FR-425]

Royal Purple has 75w - 140 for the Ford LS.

Been running it for 10,000 miles now. Works excellent. Good "slip-grip" smooth and quiet.

That reminds me! Time to change the rear diff.

 

[arco777]

RP is too rich for my blood (wallet)

 

[Chrisman889]

I have a 93 and used that same Valvoline that says it doesn't need the additive and I ended up putting in the additive just to be safe. However when I turn and accelerate I get chatter and feels like it's slipping. I'm going to try just adding it without the additive and see what happens. I also have 3.73 gears.

 

[Sonofbumperbolt]

I have used Quaker State diff lube that stated it didn't need the additive. Worked like a charm with zero problems. I have no experience with Valvoline.