I just picked up an 09 F250 a couple of weeks ago and I was planning on replacing all the fluids since I'm not sure when everything had been done in the past, but it did pull a camper 5th wheel. It has about 93000 Km/57000mi on it

One thing I noticed when reading the manual is that a rear diff fluid change is not necessary on these rear axles unless they have been submerged in water or repaired etc..

Just after I got it I noticed the pinion seal was leaking. It was fixed under warranty but the dealer did not replace the diff fluid as they said Ford will not pay for it.

My question is do you think I need to replace the diff fluid or should it still be good, given the relatively low mileage.

Thanks in advance,

 

IMO cheap insurance especially if its towed a heavy load for much or part of its almost 100K miles. Fresh fluid is never a bad thing unless were talking Wine or Bourbon.

 

I would just change it, i changed my old trucks rear end fluid at 60k miles and the fluid was nasty

 

What type of gear oil is everyone using?

 

I used Mobil 1, it has the limited slip additive in it already

 

75/140 full synthetic is whuts called for, and additive, if mobil 1 has it, thats a plus

 

Not all Mobil one has it and I wouldn't change that oil, Ford recommends changing at 150K miles otherwise it's a waste of time and money. Mine has 165k miles and is still like new.

 

Use your favorite 75W/140 synthetic. Use friction modifier or get a fluid with built in friction modifiers if you have factory LS.

 

Ya as much as I's like to leave it, common sense leads me to change it since I bought it used and really don't know how much it pulled in the past and what kind of wear it has. I'm going to go ahead and change it.

So the consensus is to use Mobil 1 synthetic 75/140 with lubricity additive?

 

That's what I used when I changed mine out and haven't noticed any issues.

 

Has anyone run a factory limited slip differential without any friction modifier?

I'm curious to know if it will do mechanical damage or will it just chatter on sharp turns?

 

It might not chatter but if it did that is stressful to the clutches and will probably damage them in time.

 

I did an oil change and used Mobil-1 75-140 synthetic that had the LS additive in it. The truck has a very minor chatter when turning sharp in cold weather. Otherwise, the limited slip rear end seems to work well.

If totally smooth operation is desired, I think that some of Ford's limited slip additive should be added to any rear end oil that already has some LS additive in it.

Next oil change will get a bit of Ford's LS additive.

Lou Braun

 

If that's all it is doing don't touch it! It doesn't get any better than that.

 

When I changed out the ring & pinion from the 3.73 LS to to a 4.30 LS I had the dealer replace the limited slip clutch's since only the right rear spun on grass and our truck was still covered by the factory warranty.

When I put it back together I filled the differential with Mobil 1 75-140 which contained the friction modifier along with just 2 oz. of Ford friction modifier.

I'm now going to install the Ford aluminum rear end cover and since we've run the new ring & pinion a season I'll probably go with new fluid (with the friction modifier) even though it's costly. I just think since we are towing relatively heavy most of the time maybe it's a good idea to change it out again since I probably won't change it again for the factory suggested mileage interval from here on.

In you guys' opinion should I add the Ford friction modifier even though the Mobil 1 contains it or just go with what the new fluid has in it?