Anyone here follow the recommended service and never change the rear differential fluid? The front calls for service every 150K, but the rear is "lubricated for life". I have done the front, but I didn't know if I should do the rear. I had it checked a while back and was told the fluid looked good.

 

Where did you find those recommendations? I found info about my Dana 80 to have the oil changed every 30k.
I rebuild my differential a year ago and changed the oil after 10k as the plug magnet had lot of steel "dust" on it.
That said my Mercedes has 220,000 miles on it and I have no records the differential was ever serviced. I am not planning to do so for the next 300,000. Only checked the oil level some time ago as it shows some oil sweating.

 

Ford Scheduled Maintenance Guide. The F-450 (Dana 80) and F-550 (Dana 135) are excluded from this and are recommended to change rear axle lubricant between 50K-100K miles.

 

Well... we had endless discussion on "lifetime transmission fluid" on Mercedes forum in section with cars made in 1995-2003. In that era average car life was less than 10 years. Now, while driving 15 years old cars the owners keep on asking "who's life we are talking about here?"
Mercedes on newer models changed the policy and advise fluid replacements.
Sure sounds like you opened another can of worms.
Good luck whenever it goes.
Oh, BTW years ago I took educational courses about oils. The main rule about oils always was "don't judge oils by their looks"

 

Change the fluid. Lifetime means until it needs a rebuild. It won't need a rebuild as soon if you change the fluid. Besides, if you've got a limited slip rear end you'll be amazed how much better the rear grabs when you put the proper amount of friction modifier in there instead of dumping in way too much like they do at the factory.

 

I change every 50-60k on a truck. Cars don't matter so much.

As far as the schedule, I don't think anyone here should be looking at the Normal Service. Severe Service applies to almost everyone. If it doesn't, you probably shouldn't be driving a truck.

Here's what I did on my Superduty.
https://www.ford-trucks.com/forums/8...with-pics.html

 

Okay, now for the friction modifier. I plan to use Valvoline Synthetic 75-140 gear oil as per the manual, do I need to use Motorcraft friction modifier? How much? I have read in two different Ford publications, one said 4oz, the other said 8oz. Which is it?

 

I suggest you choose a synthetic that has the modifier already in it. The Valvoline may, not sure. Mobil 1 and Royal Purple have it.

 

You can get the friction modifier from places like NAPA or Carquest too. Start out with 4 oz and take it for a test drive around a bunch of corners. If you're getting any chattering, add another ounce and test again until the chattering is gone. If you dump too much in there you don't have to worry about the chatter, but it also makes the LS about useless.

 

I just did mine yesterday. It also gave me a change to clean out the inside of the cover and I took them down and repainted them.

 

I'm just going to empty and fill. I'm not going to be taking it apart.

 

I can get the Valvoline for 11.99/qt and add the 4oz bottle of Motorcraft friction modifier for 6.99. The Mobil 1 and RP are both over $19/qt. No, thank you. I have NEVER used a Mobil 1 or RP product for that reason. If I am going to get into spending big bucks for fluid, I'll buy Amsoil, which I won't, I'm just sayin'...

 

Fine. Spent 20 seconds in Google to find that the Valvoline has the additive already, as I suggested that it might.
Valvoline.com > Products > Grease Gear Oil > Gear Oil > SynPower® Full Synthetic Gear Oil

Really wasn't hard to find.

 

How are you going to drain? Got a vacuum pump? Standard procedure is usually pull the cover, drain fluid, wipe things down a bit, new permatex, stick the cover back on and fill.

 

OK, but that's going to make things a bit more difficult, as there's no drain plug on these.

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