2005 FX4 LvlII Rear Diff Fluid Change

[drivenyam]

Hey guys! I have done my searching and I have read a LOT, but there seems to be a lot of back an forth on this topic and not a lot of info pertaining to my question directly.

I am changing the pinion seal AND the differential cover gasket plus my truck has over 115K miles on it. So I am looking to change the differential fluid. I have reviewed the tag on the diff and it does say "75W140 SYNTH OIL ONLY". So I get that is the fluid I need, but my question is around the friction additive. I know it's 2oz per all the specs, but which is the better to use? ALSO, I saw Royal Purple that says it has the friction additive in it already. This is the first time I have done a rear diff fluid change on any of my vehicles so I am just looking for a little guidance. Thank you in advance.

 

[85_Ranger4x4]

Level II has a different style limited slip than a regular truck. It may not require the additive, what does your manual say?

The additive won't hurt either way though.

 

[drivenyam]

I don't have my owners manual and I am pretty sure I saw the friction additive info in the tech library on here. Looking for it again to post the link.

 

[drivenyam]

Ford 8.8-Inch Rear Axle History & Specs - The Ranger Station

Usage: The Ford 8.8-Inch axle came in a few different vehicles including the: Ford Mustang (1986-2014) Ford Bronco (1983-1996) Ford F-150 (1983-2012) Ford Ranger (1990-2011 4.0L models) Ford Aerostar (1989-1997) Ford Explorer (1991-2001) (The Ford Explorer Sport still used the … Continued

www.therangerstation.com

 

[sgtsandman]

Ford 8.8-Inch Rear Axle History & Specs - The Ranger Station

Usage: The Ford 8.8-Inch axle came in a few different vehicles including the: Ford Mustang (1986-2014) Ford Bronco (1983-1996) Ford F-150 (1983-2012) Ford Ranger (1990-2011 4.0L models) Ford Aerostar (1989-1997) Ford Explorer (1991-2001) (The Ford Explorer Sport still used the … Continued

www.therangerstation.com

Note in the specs given that they mention the Torsen limited slip differential. As far as I know, Torsen only makes gear driven limited slip units, which do not require the additive. The additive won't hurt anything being in there if you get a gear oil with it already in it.

 

[rubydist]

The Torsen does not require friction modifier. As stated above, it will not hurt to add it, but why spend the money?

 

[SenorNoob]

I've never put it in my Trac-Loc with the 75-140. When I first looked into, I got the impression that was already in every variation of 75-140 at the time. Never had a problem.

 

[lil_Blue_Ford]

Yeah, most 75-140 synthetic oils have the friction modifier in it. The friction modifier is for the clutch driven limited slips to keep the clutches from grabbing hard, which makes for a smoother and quieter operation, but doesn’t let the clutches grab hard, so for a “performance” operation with the clutch driven limited slips, you want no friction modifier.

In your case, you don’t need it because you have a gear driven limited slip so it’s a non-issue

 

[drivenyam]

I appreciate the responses fellas.