Rear end noise?

[Number4]

My 2004 Explorer 4wd has started making a noise, akin to that of high lug tires or bad wheel bearings. Both of my diffs are wet, and when parked down hill I’d see a viscous grey “oil” spot on the ground.

The noise only occurs when I’m apply gas, as soon as I let off, it goes away.

I’d checked my rear diff before, and thought I’d just removed the top plug “pictured” to check. And when doing so, no fluid should come out.

Well I checked today and as soon as the plug was removed, this brown sludge looking grease started pouring out. 1. I don’t recall it being this color, 2. I thought the fill line was just below the plug.

Thoughts?

 

[Number4]

So clearly, water has gotten in to the rear diff. Perhaps via the vent hose? I’ll have to check.

 

[SixBucks]

TSB: 04-24-20
I have a 2004 4-dr, 4.0L with the towing package, so then it has limited-slip rear diff. I was getting a chattering noise when I was accelerating while turning. Kind of sounds like what you are explaining. The TSB says the rear diff needs to be removed and rebuilt.
I changed the fluid as per the TSB and it took care of my problem 100%; has been several years now.
It seems the factory fill fluid was too thin, and there was not enough put in. You drain it and refill it was Motorcraft full syn 75W140 and a bottle of friction modifier. Then, once full up to the fill plug, you need to re-install the drain plug and remove the ABS sensor on the top of the diff housing and pour more in (I think a pint, but don't quote me on that, would need to read the TSB again). A bit of a challenge to get at. It helps to remove the spare tire.
That fluid is super-expensive, but excellent stuff.
After a couple of years, my pinion seal started leaking, so I had to replace it. Has been good since.

 

[Number4]

TSB: 04-24-20
I have a 2004 4-dr, 4.0L with the towing package, so then it has limited-slip rear diff. I was getting a chattering noise when I was accelerating while turning. Kind of sounds like what you are explaining. The TSB says the rear diff needs to be removed and rebuilt.
I changed the fluid as per the TSB and it took care of my problem 100%; has been several years now.
It seems the factory fill fluid was too thin, and there was not enough put in. You drain it and refill it was Motorcraft full syn 75W140 and a bottle of friction modifier. Then, once full up to the fill plug, you need to re-install the drain plug and remove the ABS sensor on the top of the diff housing and pour more in (I think a pint, but don't quote me on that, would need to read the TSB again). A bit of a challenge to get at. It helps to remove the spare tire.
That fluid is super-expensive, but excellent stuff.
After a couple of years, my pinion seal started leaking, so I had to replace it. Has been good since.

Sounds like where I’m at. Driveline and pass axle seals are leaking now. My rig is approaching 300k and I’m really just trying to maintain and not get into it too much.

My fluid appears to have water mixed with it, not sure how it would have gotten in.

Also, my vent tube is intact and vented out of the way as it was designed. I was thinking that was where water had gotten in.

 

[FordFlintrock]

Also, my vent tube is intact and vented out of the way as it was designed.

The old rubber can get cracked especially at the tube fitting might need to trim and put a hose clamp there. There should be a clip higher up which prolly rusted away to keep it vertical or it will fold over while driving from the wind. The open end after the loop should be facing rearward and finally check the fitting that screws into the axle tube they can get loose.

 

[Number4]

Well, I drained and refilled it today with the proper fluid. I filled it up until it started coming out of the drain hole and that’s as much as I put in. I did not remove the ABS sensor and add any additional via the top. It is making the same exact sound. The sound is speed related and goes away as soon as I let off on the gas.