Diff fluid change w/ Royal Purple. Add extra friction modifier?

Mwilbur516 · Jan 2, 2012

I'm about to change my diff. fluid and I'm using Royal Purple. It states that it already has the friction modifier and I wasn't planning on adding any more until I got to reading a post on the .org that states even when a fluid has the friction modifier you should still add more. Is there any truth to this? Has anyone changed to Royal Purple without adding anything and had any problems?

8luggin · Jan 3, 2012

i changed mine when i did the mag hytecs over a month ago and no problem

PatriotHauling · Jan 3, 2012

I used Valvoline which has the LS additive. No problems on and off road, mud snow and asphalt.

Sent from my iPhone

John@Outlaw_Diesel · Jan 3, 2012

I added some when I used royal purple. For price of additive, thought it was worth added assurance.

Spastik monkey · Jan 3, 2012

it's all up to how the diff takes it. change the fluid with RP, and drive it. If you don't feel the rear end is working as it should, add some modifier. RP varies truck to truck on how well their included modifier works

Mdub707 · Jan 3, 2012

I haven't heard/read any good things about the RP fluids. I'm pretty sure there was a guy on PSN who did quite a few oil analysis samples on his rear end fluids, as he towed heavy all the time and the RP did NOT fair well at all.

As for the friction modifier, I can't believe it'd be correct right out of the bottle. Most of the Ford rear-ends I've had to change fluid in that required the LSD additive, didn't require as much as typical LSD's. So some are different than others, how can one bottle cover them all?

07_powerstroke · Jan 3, 2012

I thought all the friction modifier did was make it spin one tire more than the other.

Mwilbur516 · Jan 3, 2012

I was looking to use Royal Purple because of the reviews I read online and in magazines. Personally, I've always used Mobil1. I'm open to any and all suggestions on fluid type. What are you guys using and liking?

wetnsloppy4x · Jan 3, 2012

07_powerstroke said:
I thought all the friction modifier did was make it spin one tire more than the other.

Lol. Seems that way sometimes. Its really meant to let the clutches slip smoothly instead of chattering when turning and such.

Mwilbur516 said:
I was looking to use Royal Purple because of the reviews I read online and in magazines. Personally, I've always used Mobil1. I'm open to any and all suggestions on fluid type. What are you guys using and liking?

I recently put in the Valvoline synthetic along with two bottles of Ford friction modifier. I have zero chatter turning and the limited slip locks up nicely in a straight line. Even on 37"s. Time will tell how it holds up.

This is on a diff that has about 80k on it. The diff it replaced had 100k on it when I sheared the pinion. That one, with it's original fluid, was a one tire fire from hell. It couldn't posi up to save its life. It had been that way since I bought the truck @ 53k.

I guess my point is the way the diff behaves probably depends more on its history than what brand fluid is in it.

lincolnlocker · Jan 3, 2012

amsoil here.. asmoil even recommends adding friction modifier to their oil...

Mwilbur516 · Jan 3, 2012

Alright, I think I'm goin' to pick up a couple bottles of Ford friction modifier, but I found to different part numbers. Anyone know which one it is? Here are the part numbers I came up with-
M-19546-A1

XL-3 135454

bboteler · Jan 4, 2012

:whs:

Zmann · Jan 4, 2012

Manufacturer: Ford / Motorcraft
Item Number: FOXL3

us the modifier only if you get a chatter around a corner it actually free's up the clutches and since your using RP and your clutches are probably worn you may not need it
also if u even open the bottle triple bag it in a sandwich bag
this will be the stinkiest fluid you ever smell IMHO

Mdub707 · Jan 4, 2012

Amsoil and Schaffers seemed to get good reviews/analysis. I'll see if I can find the thread...

Mdub707 · Jan 4, 2012

http://powerstrokenation.com/forums/showthread.php?t=50496&highlight=diff+oil+analysis

Mwilbur516 · Jan 4, 2012

Good thread Mdub. I'm gonna look into the Amsoil instead of RP. Just gotta find somewhere that sells it. I'd like to find it in stock somewhere.

wetnsloppy4x · Jan 4, 2012

Zmann said:
also if u even open the bottle triple bag it in a sandwich bag
this will be the stinkiest fluid you ever smell IMHO

:whs:
Your shop will smell like cat piss with that stuff around.

Zmann · Jan 4, 2012

good call
thats about it x 10 .

I wouldn't be spending all kind of time looking for fancy fluid

ford or IIRC mobil 1 have the spec'ed viscosity in a syn and it is just fine

Mwilbur516 · Jan 21, 2012

Having a really hard time finding the Amsoil, and where I do find it the dealers want me to order 2 cases. Not happening. I looked into the RP a little more and kinda doubt I'll go that route.

lincolnlocker · Jan 21, 2012

Mwilbur516 said:
Having a really hard time finding the Amsoil, and where I do find it the dealers want me to order 2 cases. Not happening. I looked into the RP a little more and kinda doubt I'll go that route.

My cousin is a dealer. If you want I can give you his number and he will take your info over the phone and have what u want sent to your doorstep.... also I'm sure there's a few vendors on here that will send u what u need also.