Hello! This is my first post to this forum. The issue I am having is a loud whining noise that seems to be originating from the rear of my truck. I also note that my truck turns roughly to either side as if it is stuck in four wheel drive. I checked the four wheel drive system and it is functioning properly which leads me to believe this might be related to the rear differential. I am unsure how to properly diagnose the differential.

 

Bet the clutch packs are blown in the rear diff.

 

I was concerned that someone would bring that up. Seems to be a pretty common problem with these trucks.

 

On the 2011's and newer it's hard to find a L/S diff. Most of the newer trucks have an open diff. w/ an optional an E-locker.

Depending on how much $$ they want to replace your clutch packs...I'd consider replacing the whole carrier with an Eaton TrueTrac. No more clutches to replace.

http://www.ebay.com/itm/Eaton-Detroi...lV~BpO&vxp=mtr

 

So I changed my differential fluid and used Royal Purple with one 4oz tube of Ford friction reducer. About 90% of the symptoms have gone away, but they are still there. Thoughts?

 

Give the modifier more time to work itself into the clutches - if it doesn't go away in a couple weeks, put another tube of modifier in.

 

Every 4x4 has the ls, not so uncommon.

 

Pretty sure your still screwed. Get the true trac ls diff......totally worth it's weight in gold! Get the mag hytec diff cover too!

 

My 2011 and 2014 FX4's had open diff w/ e-locker. I hated it so I installed a Truetrac in both trucks.

 

Nope, it's an option. The 2011s had the option of a LS or E locker depending on the trim level. For example, a King Ranch had the open as standard with an optional locker. The Platinum had an open as standard with the LS as an option. Neither was available with all three options. I went all through this when ordering my truck.

Starting in 2012 the LS was phased out.