2003 Rear Differential Fluid Type?
Fleet Owner
Joined: Apr 2008
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From: 0,0,1
According to your owner's manual, it's 75W-140 synthetic if you have a limited slip rear axle. For the non-limited slip rear axle you would use 75W-90 synthetic.
Laughing Gas
Joined: Jan 2003
Posts: 1,082
Likes: 40
From: Melbourne, FL
Don't top it off just because it's "low". The fluid level is supposed to be a certain measurement below the fill hole. I don't remember the measurement, but it should be in that dvd service manual you have.
Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
The 8.8" diff calls for Synthetic SAE 75W-140 with Traction-Lok or non-synthetic SAE 75W-90 without Traction-Lok.
If you have a front diff Ford specs a non-synthetic SAE 75W-90 for the front diff.
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Elder User
Joined: Jul 2003
Posts: 746
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From: Salisbury, MD
As to the Friction Modifier, one place in the DVD it says XL-7 (as of 4/30/2003) but elsewhere it says XL-3 (as of 1/28/2002). What's the correct Friction Modifier, i'm assuming XL-7 since it has a newer revision date.
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Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
I can't find my manual at the moment, but 0.9" sounds excessive, but it may be correct. Make sure that when you looked it up it wasn't 9mm, which would be between 0.3" and 0.4" below the fill hole.
I'm not aware of the difference between the XL-3 and XL-7, but as 1/28/2002 I don't believe Ford had used the IRS in the Expy, so I'd agree with your assumption that XL-7 is correct for the IRS diff. 
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Laughing Gas
Joined: Jun 2003
Posts: 1,218
Likes: 2
From: Parkville, MO (KC)
.9" is right for 2004 at least.
My local ford counter man -- pretty large and sucesful place -- says that the 75w140 synth is now standard and superceeds the older heavy diff fluids, regardless what your old manual or shop manual says. He has a ford counter manual that shows that.
So you can run the 75w140 up front too...
Ditto all the comments about needing LSD additive. I have a leaky rear. I've decided to mix up a quart of lube with additive so I can top it off (.9" below) whenever I need to.
And BTW, I too find it just plain stupid for Ford to design a diff case, where you have to use a wire bent like an "L" to find the fluid level. Like -- whatever happend to the good ole days where you filled to level of the filler hole and then you knew you had the right ammount in there......
My local ford counter man -- pretty large and sucesful place -- says that the 75w140 synth is now standard and superceeds the older heavy diff fluids, regardless what your old manual or shop manual says. He has a ford counter manual that shows that.
So you can run the 75w140 up front too...
Ditto all the comments about needing LSD additive. I have a leaky rear. I've decided to mix up a quart of lube with additive so I can top it off (.9" below) whenever I need to.
And BTW, I too find it just plain stupid for Ford to design a diff case, where you have to use a wire bent like an "L" to find the fluid level. Like -- whatever happend to the good ole days where you filled to level of the filler hole and then you knew you had the right ammount in there......
Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
Thanks for the confirmation. 
Exactly! And how about the way Ford threatens your warranty if you use the wrong spec fluid, and then all of a sudden its okay (like the Mercon/Mercon V confusion)? Makes one wonder how important their 'spec" is. 
Elder User
Joined: May 2011
Posts: 527
Likes: 0
I just do it like I've always done, use a pump to fill through the fill hole until fluid starts to spill out, put the plug back in, done. I've never and have never heard of anyone having a problem doing it this way.
I also run full syn in front and back, 75w-90 front, 75w-140 rear with a tube of friction modifier mixed up in the first quart to go in each of them.
I drained/filled each diff when I first got the vehicle, part of routine maintenance for any used rwd/4wd vehicle I buy. That and the TC/trans fluid and transfer case as well...
edit: and you don't want to "top off" diff fluid. If its low and was filled properly its leaking and needs a new gasket or cover or both. If it isn't leaking it wasn't filled properly. Either way its best to just drain all the old funky fluid out and give your vehicle new fresh stuff that'll last you a while.
I also run full syn in front and back, 75w-90 front, 75w-140 rear with a tube of friction modifier mixed up in the first quart to go in each of them.
I drained/filled each diff when I first got the vehicle, part of routine maintenance for any used rwd/4wd vehicle I buy. That and the TC/trans fluid and transfer case as well...
edit: and you don't want to "top off" diff fluid. If its low and was filled properly its leaking and needs a new gasket or cover or both. If it isn't leaking it wasn't filled properly. Either way its best to just drain all the old funky fluid out and give your vehicle new fresh stuff that'll last you a while.
Fleet Owner
Joined: Apr 2008
Posts: 24,324
Likes: 5,136
From: 0,0,1
The reason for the change was cosmetic. When the fluid levels were up at the filler hole, fluid always seemed to ooze out and look unsightly. By lowering the fluid level it kept the fluid away from the filler threads.
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