So my mom has a 2006 Ford Explorer she wants the fluids changed in. It's the XLT model with 4 wheel drive, and I have a couple of questions.

1) I recommended Royal Purple 80W-90 (the Chilton manual says 80W-90 for the front axle, and 75W-140 for the rear diff) for the front axle. It has what appears to be a differential cover you can just pop off to drain the old fluid and examine the gears for wear. She couldn't find Royal Purple, (which also contains friction modifier), so she got this: Heavy Duty 80W-90 Gear Oil

My question is, does the front axle need friction modifier, or is it fine with just straight 80W-90 gear oil?

2) I was told years ago by some guy in a repair shop that the transfer case and transmission "share" fluid. I'm getting ready to drain and re-fill her transfer case, but beyond just peeking at it real quick to make sure of where it was at, I've never messed with it or closely examined it. Does it in fact share fluid with the transmission? If so, then that means we'd have to flush the transmission and transfer case at the same time, or else wouldn't draining the transfer case alone just mean we'd have a small amount of new fluid being mixed in with old fluid? I'm thinking it shouldn't "share" fluid because the Chilton manual recommends two different types of automatic transmission fluid for the transmission and the transfer case, but thought I'd ask.

3) She was told by a guy at Advance that they don't sell a gasket for the cover on the front axle. Would high temp RTV/gasket sealer by itself work to re-seal that cover? There is no drain plug as far as I can tell, just the fill plug on the front cover that I'll be removing to drain it and examine the condition of the gears inside (there's a popping noise occasionally and we're trying to narrow down where it's coming from).

Next week or the week after I'll be doing the rear differential, and she's gonna pay somebody to do the transmission so they can suction out all of the fluid, but this week I'm supposed to do her front axle and transfer case, so just figured I'd verify a few things before I got started.

 

Don't know if the 2006 is like the 2002, but there is no room to get the front cover off the 2002. You can suck the oil out of the fill hole and add some new, but that's all... 80-90 is OK. No addative needed.
Rear has a drain and a fill plug. You need 75 w 140 synthetic in the rear.

 

Yeah just got around to it today. Drained and filled the transfer case with Royal Purple automatic transmission fluid, drained and re-filled the rear differential with Royal Purple 75W-140, and topped off the front differential with 80W-90. I bought the Chilton's manual for it years ago when I had it so it lists all the fluid types and capacities, etc.. I wanted to take off the cover on the front axle because there's been a popping noise going on for a while now, but only under certain circumstances, so I wanted to visually inspect the gears and stuff in there. She had to be at work today though, so I just topped it off since it was about 1/2 quart low so she could get to work on time.

The drain plug for the rear differential was honking huge, took a 1" ratchet. problem is, a 1" ratchet is, as you can imagine, fairly large, almost as thick as the very narrow space between the differential cover and a crossmember, so I could only back it out two or three turns with the ratchet before I could no longer remove the ratchet, so I had to loosen it and turn it enough with the ratchet to no longer be flush, then use some large channel locks to grip around it and twist it out far enough to be removed with my fingers. Good thing about being so huge though is that although you can't see much, if the rear wheels had been suspended I could have put the transmission in neutral and twisted the drive shaft and examined the ring gear without having to remove the cover and mess with replacing the gasket.