How much diff lube do I get?? What brand to get...? Rearend whine/roar....

[thepotroast]

I had the ring and pinion gears changed twice under warranty still the noise is there... i will just try to tune it out with some good ol tunes...Hey the speakers still work fine.

This is pretty much the consensus here....no guarantee that if you get the parts replaced, that you won't get the same ring/pinion part that was machined from the worn equipment that the supplier originally made. I don't even know if Ford ever produced a second set of ring/pinions from another supplier...likely all of the stuff in their arsenal of OEM parts are from the original supplier(s)...so you will be paying for nothing.

 

[Oldwolf]

I'm getting ready to change my fluid with the Mobil 1 75w-140 LS formula. I was told I wouldn't need friction modifier since it is already part of the chemistry.

 

[IZwack]

I had the ring and pinion gears changed twice under warranty still the noise is there... i will just try to tune it out with some good ol tunes...Hey the speakers still work fine.

I would try another dealer/shop - setting up gears takes hours and sometimes people get lazy.
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[thepotroast]

I'm getting ready to change my fluid with the Mobil 1 75w-140 LS formula. I was told I wouldn't need friction modifier since it is already part of the chemistry.

That is correct, the Mobil 1 has friction modifier in it, however others on here suggest adding additional friction modifier. I put in 7oz in addition to 1 quart of the Mobil 1 75w-140 and that seemed to top things off in the rear diff nicely.

 

[Oldwolf]

I see that you used the CRC product, I saw that at Autozone too. I wonder if the CRC stuff is in a synthetic oil base?

 

[EasyRhino]

FWIW, my 2002 Limited 4.6 V8 AWD w/ 3.73 gears has had the whine since new, never got better, never got worse. As was stated previously, my best fix was to use the premium stereo system to ignore it.

I did the first fluid chnage at 100,000 miles. No surprises and pretty easy. Used Mobil 1 Synthetic 75W-140 ($25 a quart over here), and no difference. The old oil didn't look that bad actually.

I'll continue until 200K miles as is unless it lets go!

 

[NOPSTNS]

I just changed out my front and rerar diff fluids. I put Quakerstate 75W140 full synthetic in both and 4 oz. modifier in the rear. The fricton modifier came from Ford. It was only 3 dollars. I have no more noise or rumbling coming from the rear end when I accelerate, cruise etc. It feels like a new truck.

 

[Oldwolf]

Don't forget to change the ATF in the transfer case. I dumped mine out at 80k and it was pretty nasty. I used petro ATF last time but I think when I do it again I'll use synthetic. It only took 1.5 qts iirc.