Notices
6.0L Power Stroke Diesel 2003 - 2007 F250, F350 pickup and F350+ Cab Chassis, 2003 - 2005 Excursion and 2003 - 2009 van

Rear Diff Flud

Old Jul 6, 2017 | 10:02 AM
  #1  
akblackfoot's Avatar
akblackfoot
Thread Starter
|
More Turbo
10 Year Member
Photogenic
Joined: Mar 2016
Posts: 643
Likes: 6
Rear Diff Flud

Change the fluid in my differentials a couple weekends ago. I used Mobile 1 Synthetic 75W-140LS in my rear diff. Said it has the friction modifier in it and I haven't noticed anything odd or out of the ordinary after changing it. Had some people claim you still have to add friction modifier or it will screw up the rear end. Any truth to that?
 
Reply
Old Jul 6, 2017 | 10:09 AM
  #2  
Blakshukvw's Avatar
Blakshukvw
Elder User
Joined: Jul 2016
Posts: 646
Likes: 4
From: Blue Springs, mo
You should be ok if it had modifier in it. The Amsoil is the same way. I personally use it in my truck's but I still add some modifier anyway. It won't hurt to add additional modifier.
 
Reply
Old Jul 6, 2017 | 10:41 AM
  #3  
MisterCMK's Avatar
MisterCMK
Fleet Owner
20 Year Member
Photogenic
Photoriffic
Liked
Joined: Mar 2003
Posts: 24,724
Likes: 74
From: Blue Hill Township
If it isn't chattering there is no reason to add any.

Adding more will make the limited slip unit less effective.
 
Reply
Old Jul 6, 2017 | 11:32 AM
  #4  
bismic's Avatar
bismic
Fleet Owner
Community Builder
Liked
Loved
Community Favorite
Joined: Nov 2003
Posts: 27,900
Likes: 3,617
Club FTE Gold Member
From 50k miles on, I have uses the Mobil 1 Synthetic 75W-140LS also. Never have added extra friction modifier to it. 194k miles now, no issues.
 
Reply
Old Jul 6, 2017 | 12:30 PM
  #5  
akblackfoot's Avatar
akblackfoot
Thread Starter
|
More Turbo
10 Year Member
Photogenic
Joined: Mar 2016
Posts: 643
Likes: 6
Thanks everybody. I was pretty sure this was the case but just needed some confirmation from more knowledgeable people.
 
Reply
Old Jul 7, 2017 | 04:48 PM
  #6  
Pest007's Avatar
Pest007
Tuned
20 Year Member
Joined: Jun 2004
Posts: 472
Likes: 4
From: Goodyear, AZ
How much does it take to change? I'm needing to change mine and want to buy the upgraded Ford diff cover with the cooling fins
 
Reply
Old Jul 7, 2017 | 06:31 PM
  #7  
akblackfoot's Avatar
akblackfoot
Thread Starter
|
More Turbo
10 Year Member
Photogenic
Joined: Mar 2016
Posts: 643
Likes: 6
3.5 quarts or so. Got 4 and had some left over.
 
Reply
Old Jul 8, 2017 | 10:18 AM
  #8  
amdriven2liv's Avatar
amdriven2liv
I'm hitting easy street
15 Year Member
Photogenic
Photoriffic
Shutterbug
Joined: Nov 2009
Posts: 6,395
Likes: 27
From: Central Oregon
Club FTE Silver Member

I used the Valvoline oil for limited slip. Every thing was fine until I started pulling this trailer around the country. I had to add 1 bottle of fords additive. Just thought I should pass this along.
 
Reply
FTE Stories

Ford Trucks for Ford Truck Enthusiasts

story-0

10 Things Every Truck Owner NEEDS (2026 Edition)

 Michael S. Palmer
story-1

Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath

 Verdad Gallardo
story-2

Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer

 Joe Kucinski
story-3

2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)

 Brett Foote
story-4

Top 10 Ford Truck Tragedies

 Joe Kucinski
story-5

AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make

 Brett Foote
story-6

Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!

 Michael S. Palmer
story-7

Ford's 2001 Explorer Sportsman Concept Looks For a New Home

 Verdad Gallardo
story-8

10 Best Ford Truck Engines We Miss the Most!

 Joe Kucinski
story-9

2026 Shelby F-150 Off-Road: Better Than a Raptor R?

 Brett Foote
Old Jul 8, 2017 | 09:14 PM
  #9  
Dr.Huxtable's Avatar
Dr.Huxtable
Senior User
Joined: Nov 2015
Posts: 370
Likes: 0
From: Spartanburg, SC
Ugh this thread just reminded me I need to do this. Been putting it off because I wanna upgrade the cover at the same time. Money and time, two things there's never enough of!
 
Reply
Old Jul 9, 2017 | 08:12 AM
  #10  
DSMMH's Avatar
DSMMH
Fleet Mechanic
Joined: Jun 2006
Posts: 1,589
Likes: 20
I upgraded the diff cover several years ago. The new capacity is 6 quarts. I use Royal Purple 75W-140 and two years ago added AR9100. That took care of a chattering problem I had.

Ed
 
Reply
Old Jul 9, 2017 | 04:27 PM
  #11  
akblackfoot's Avatar
akblackfoot
Thread Starter
|
More Turbo
10 Year Member
Photogenic
Joined: Mar 2016
Posts: 643
Likes: 6
I have the Ford aluminum diff cover and it took less than 4 quarts so I'm sure it depends on which one you have.
 
Reply
Old Jul 9, 2017 | 06:14 PM
  #12  
TooManyToys.'s Avatar
TooManyToys.
Hotshot
Photogenic
Photoriffic
Shutterbug
Joined: Dec 2014
Posts: 17,828
Likes: 3,113
From: Jersey Shore
No matter the cover, the bottom of the fill port in the diff is the correct amount for coverage.

At 100k I ent no additive as y limited slip was limited no more. Didn't change by not using the additive. At some point I'll pull the clutches and replace.
 
Reply
Old Jul 10, 2017 | 10:29 AM
  #13  
jlillie's Avatar
jlillie
Mountain Pass
20 Year Member
Joined: Nov 2002
Posts: 242
Likes: 8
From: Cape Coral USA
I just did mine. Got the aluminum cover, put a black paint job on it, with the stainless allen head bolts. Used Amsoil with most of a bottle of friction modifier, but the point i wanted to make is i also used a Lube Locker gasket which saved me from having to use permatex and waiting 24hrs before i could add the oil back. No leaks so far.
 
Reply
Old Jul 10, 2017 | 02:59 PM
  #14  
MisterCMK's Avatar
MisterCMK
Fleet Owner
20 Year Member
Photogenic
Photoriffic
Liked
Joined: Mar 2003
Posts: 24,724
Likes: 74
From: Blue Hill Township
If you're going through the trouble of opening up the differential, you might as well toss a true trac in there and have a traction device that actually works and then never worry about friction modifier ever again.
 
Reply
Old Jul 10, 2017 | 03:14 PM
  #15  
wedge542's Avatar
wedge542
Laughing Gas
Joined: Jan 2007
Posts: 883
Likes: 5
Originally Posted by MisterCMK
If you're going through the trouble of opening up the differential, you might as well toss a true trac in there and have a traction device that actually works and then never worry about friction modifier ever again.
Do you have one in yours,it doing ok on the street or towing heavy, im installing clutches,side gears,spider and gears in mine now but with 340k guess its time.
 
Reply

Thread Tools
Search this Thread

All times are GMT -5. The time now is 03:16 AM.

story-0
10 Things Every Truck Owner NEEDS (2026 Edition)

Slideshow: the best gifts for dads & grads

By Michael S. Palmer | 2026-06-02 21:45:57


VIEW MORE
story-1
Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath

Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.

By Verdad Gallardo | 2026-05-30 18:33:59


VIEW MORE
story-2
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer

Slideshow: 10 most expensive Ford trucks ever sold on Bring a Trailer.

By Joe Kucinski | 2026-05-27 16:24:34


VIEW MORE
story-3
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)

Here's everything that has changed for the latest model year.

By Brett Foote | 2026-05-27 16:17:28


VIEW MORE
story-4
Top 10 Ford Truck Tragedies

Slideshow: Top 10 Ford truck tragedies.

By Joe Kucinski | 2026-05-18 19:34:33


VIEW MORE
story-5
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make

And it might be even better than that.

By Brett Foote | 2026-05-18 19:26:42


VIEW MORE
story-6
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!

Slideshow: Does lowering an F-150 Lobo RUIN the ride quality?

By Michael S. Palmer | 2026-05-18 19:20:37


VIEW MORE
story-7
Ford's 2001 Explorer Sportsman Concept Looks For a New Home

Slideshow: Ford's bizarre fishing-themed Explorer concept has resurfaced after spending decades largely forgotten.

By Verdad Gallardo | 2026-05-12 18:07:46


VIEW MORE
story-8
10 Best Ford Truck Engines We Miss the Most!

Slideshow: The 10 best Ford truck engines we miss the most.

By Joe Kucinski | 2026-05-12 13:09:47


VIEW MORE
story-9
2026 Shelby F-150 Off-Road: Better Than a Raptor R?

Slideshow: first look at the 810 hp 2026 Shelby F-150 Off-Road!

By Brett Foote | 2026-05-12 12:50:07


VIEW MORE