Differential fluid change - do I need friction modifier?

[BANE]

amsoil 75w140 is good stuff

 

[MTF]

I'll just leave this here for you guys that are still confused about where and what goes in the two axles.

https://www.fcsdchemicalsandlubricants.com/Main/quickref.asp

 

[Mohegan]

Friction modifier in a Ford 9.75 rear diff with e locker (2014 Roush Raptor)WILL destroy your e locker...$675.00 for replacement parts.

 

[MTF]

Updated Ford Official Gear Oil Charts:

 

[MrSkunks]

Just changed my rear dif with Royal Purple 75w140 Gear Oil.

Didn’t realize it wasn’t required but I know noticed that it did include the friction modifier.

Is this going to damage anything? Should I reflush it?

 

[MTF]

Friction modifier in a Ford 9.75 rear diff with e locker (2014 Roush Raptor)WILL destroy your e locker...$675.00 for replacement parts.

@MrSkunks I wish I could tell you with out a doubt you'll be OK, but.....

I had a problem with Royal Purple in my 67 Buick GS with a highly modified T400 transmission.
I had nothing but slippage, went back to the speed shop that built it and he said RP is garbage.
Fluid was burnt in one and half weeks. Luckily the B&M clutch packs were still good.
Did a complete fluid flush with Ford ATF.
He then told me Ford transmission fluid is what all the track guys use in GM trannies.
And he was right.

 

[HotLap]

FWIW, when I installed the Ford Performance rear diff cover, (2018 Raptor), I was wondering about the need for a friction modifier even though the install instructions did NOT call for it. So I called Ford Performance directly and they confirmed NOT to use any friction modifier. 8K miles later all is fine...

 

[pastorwug]

FWIW, when I installed the Ford Performance rear diff cover, (2018 Raptor), I was wondering about the need for a friction modifier even though the install instructions did NOT call for it. So I called Ford Performance directly and they confirmed NOT to use any friction modifier. 8K miles later all is fine...

How many quarts are needed for the Ford Performance cover? AND - did you use the upper fill hole or lower fill hole?
I bought 4 quarts of the Amsoil Syn 75/140 and hope that was enough, it was just starting to weep out of the upper fill hole.

 

[HotLap]

How many quarts are needed for the Ford Performance cover? AND - did you use the upper fill hole or lower fill hole?
I bought 4 quarts of the Amsoil Syn 75/140 and hope that was enough, it was just starting to weep out of the upper fill hole.

Hey PWug, sorry just seeing this. I can't exactly recall the amount to fill, but it was, (IIRC), just under 3 quarts? I used the Ford fluid (expensive) and FP says to use the bottom hole (unless you truck is lifted) then to use the upper fill hole. Great Looking cover and super easy install...any questions, call Ford Performance, they are great to assist with any advice on FP vehicles or parts...I haven't called in a while, but here's the number 800.367.3788.

Good Luck

PS. Double check me on this, but pretty sure the FP Diff cover does not add any additional capacity so refill is same as stock amount...

 

[MTF]

The top hole is used for a cooling system.

https://performanceparts.ford.com/part/M-4000-M8S

https://www.maximummotorsports.com/MM-Cobra-IRS-Differential-Cooler-Kit-P1077.aspx