Hello, first let me introduce myself. I recently had to sell my 1990 Ford Bronco (hence my name) because it failed emissions six times and I gave up. I bought a 2004 Explorer 4X4 with 93K for $7,200. I am very happy with my new truck. It is very clean and looks like new. I only noticed one thing - a slight whine from the rear end at 55 mph when I am on the gas. It doesn't really sound like a bearing. I read somewhere that Ford put a lighter weight gear oil in the diffs to increase fuel economy, and if you put in a heavier grade then the whine will go away. Is this true? If so, what should I use? The whine is barely noticeable and doesn't bother me, but if it could be eliminated easily by changing the oil I'd do it. I also read that someone did this and a week later the diff blew up. I'd rather have a very slight whine than a diff blowing up! What should I do here? Thank you!

 

I noticed not too long ago that my 06 has developed that same whine at cruising speeds. I never noticed it before but I hadn't driven it much before with the radio off which does mask the sound. I assumed it was the hub bearings but never thought about the rear differential.

 

bearings will make noise at 30- 40- 50, etc MPH. If the noise comes on at 55-60 mph, see if it goes away at 70-75 MPH. It could be gear whine. Changing the rear end oil charactoristics can help. I keep 75-w140 in it and added friction modifier. That helps. I also run it 1/2 inch overfull, that can help. Possibly a different oil would help. 80-90 seems to be worse for noise. Full synthetic seems to help ?? JUst my experience. Make sure the alxe is FULL... add a cup and see if that helps.

 

Thanks. It only does it at 55 mph. Can you tell me what the rear end's diff capacity is (with oil and friction modifier)? I haven't picked up any manuals for this truck yet. And how can you overfill it? Don't you fill up a diff until it reaches the fill hole?

 

The 2004 factory service manual (updated in 2008) calls for SAE 75W-140 High Performance Rear Axle Lubricant XY-75W140-QL lubricant meeting specification WSL-M2C192-A, quantity 1.65 liters/3.5 pints. For Friction Modifier additive it calls out XL-3, specification EST-M2C118-A, quantity 0.12 liters/0.25 pints.

Assuming you are using a jack and jackstands to fill the rear differential, to overfill the differential you would just jack up the side with the fill plug higher than the other side and support with a jackstand. You are correct, generally the fill capacity is considered to be just below the fill plug opening when the vehicle is level.

-Rod

 

I had a 2004 that had the same problem. The rear-end whine appears at 55 and goes away at about 65. It only whines when you have the gas under a slight throttle and when you lift it goes away. I did all the research and changed the oil with no noticeable change. Further research uncovered this as a common problem and if oil change doesn't help, your only option is to replace the rear end gears. The shop that did mine explained the older ford parts where made in US but the newer ones came from Chine and the tolerances/etc. are not as good as what they were. After the new gears were installed my rear end made more noise than before and the shop replaced everything again. The noise remained. They would not do the job the third time unless I wanted to buy the gear set from an after market/off road, etc. company. They told me they had encountered this problem on other owners Explorers so they knew the problem wasn't just my vehicle. I decided not to spend more money on the issue and unfortunately the Explorer was totaled the following month by a drunk driver. Because the Explorer is a solid vehicle built on a truuck frame and the police said the wife was very lucky she wasn't driving something of less bulk, we took the insurance money and bought a 2006 Explorer. It doesn't have the rear end whine but it does have the famous Ford smack down shift from 2nd to 1st gear. Of course Ford denies it is a problem.
If the oil change doesn't help, at least you know what you options are now.

 

I'm sorry about your problems with gears and accidents. But thanks for the reply. I really don't care about the small noise enough to bury myself in parts and repairs. It's -only- at 55 mph, not 56 or 54 or any other speed. I'd imagine that it's been that way since new. I have other, non-truck related problems to worry about, we all do, so this isn't an issue. After owning my Bronco for 12 years this feels like a brand new truck for me and I'm not starting in with needless repairs that, according to you and other posts and articles I've read, are common and repairs often generate more and more issues like what happened with yours. So the h*ll with it! BTW - mine shifts smoothly through all five gears (knock on wood) and I don't have any of the noises or hard shifts that I keep reading about. So actually I feel lucky! I'm not going to mess with the diff at all. I'm just going to drive it and be happy.

 

if you get ambitious you can change the oil as that won't harm a thing and sooner or later you need to do it anyway.

My whine was much more pronounced than yours so ignore it unless it gets worse.

 

Can somebody please tell me this, as I have not yet purchased a manual for my almost new Explorer (2004, 93K, 4.0 V6, 5 speed auto, 3.73 gears, IRS, 4X4). I need to know about draining/refilling the rear diff. It looks like it has a drain plug which is very big and not all the way on the bottom, and then a bit higher up and a bit to the right, it looks like a fill hole. Are those in fact the drain and fill holes? They both have square drive plugs (I hope I have a square drive socket big enough if the big one is indeed the drain hole). Also, what is the procedure for filling the diff? There's hardly any room between the diff and the IRS arm. I figured that an oil change is a necessity anyway so I may as well put new oil/friction modifier in there. Thanks.

 

I will respond but I will bet others do with all the info you need.

I did mine a year ago so I probably forgot things..........The top plug is for refilling and the bottom one is for draining. you can get to both of them with a socket wrench and I believe they are the 1/2" size that is the standard for sockets. I don't think it was the 1/4" but you can figure it out. I had to put an extension to get onto the one plug and can't remember whether it was 2, 4 or 6 inches.

Drain when the fuild is warm and I had a small hose that I attached to a little hand pump and inserted it after it drained and sucked out everything else I could get as the bottom bit of fluid is the dirtiest. Fill back up until it just starts to run out the hole (top one of course).

 

Thank you for the help, all of you! Now, I may not even remove the lower plug, I have a pump to suck the oil out. The bottom plug looks pretty big, maybe it needs a 3/4" drive and I only have up to 1/2" drive (although I've been meaning to get myself a 3/4 socket set). I do have a set of square plug sockets and maybe one is big enough for the drain. I'll get it off. But the biggest problem I see is that the fill hole is blocked by the independent rear suspension. I don't know what year yours is, but if it has a live rear axle then I don't think there would be a problem getting the fluid in. So, even with a pump and hose, if I use that to fill it, it's very close and even that might not work. I'll have to take another look and see what tools I need. The whine on my Explorer is so slight that I really don't care about it. I'm just happy to have a new(er) vehicle to drive and not need to fix something all the time. I was always working on my Bronco and it paid me back by by failing six emissions tests. I took good care of it, but in the end the Bronco screwed me. I spent $75 for three emissions tests and three free retests within ten days; plus all that money for repairs that we thought might do the trick. Actually the Bronco was a money pit forever. but at least I knew what had been done. The list of new parts is endless. So it's too bad it kept failing - every single thing on that truck worked properly, it had $1,700 in new Michelins that had maybe 1,000 miles on them and Alcoa-type rims and over $1,000 for the stereo. The truck had absolutely no rust- it needed NOTHING except to pass that d@mn emissions test and maybe paint it, although it still shines except for the hood. Anyway, I sold it to a kid for $1,500; I had to, because at the end of the month I would have had an undriveable Bronco sitting in the driveway, and I share a house so I could not do that. And I had just finished overhauling the Bronco's A/C, I put in all new factory oem parts and it cost me over $600, just a couple of weeks before the emissions testing. But I'm not going to get bogged down in telling you everything I repaired or replaced in the 12 years I owned my Bronco, just figure that it was A LOT and that there wasn't anything that needed to be done when the kid bought it except to pass the emissions test. That's it. The Bronco was cherry and had all sorts of extras, but I don't miss the constant repairs and shelling out of money. It got to be like a bad marriage; one day, after it failed six tests, I decided to stop putting good money after bad and that the time had come to sell it. I finally gave up. Once I made that decision I couldn't wait to sell it... So now I have my Explorer - something that I am going to drive and not get started in on all the proactive repairs, I just plan to drive it and if something happens to break I'll fix it. But I feel like a got a good one. At 93K it feels very tight, and if you look underneath the truck there is not a drop of oil or anything on there, it's as dry as a bone and looks factory clean. And my 5 speed automatic works flawlessly; no hard jerks or noises or slipping, no inappropriate downshifts etc. But that kid got a great deal on the Bronco even if, like I and a mechanic suspected, it needs a new motor to pass emissions (although the 160K motor in it didn't burn oil and idled so smoothly that sometimes I had to look at the tach to see if it was still on!). The kid's whole family are mechanics and have the space to do the job if necessary. So that's probably no big thing for him. But there was no way I could do an engine swap where I live - just take my word for it. The Bronco was my daily driver and at the end of the month I would have been stuck and it would have been much harder to sell and I'd probably would have had to take even less (although if it came to that I was going to pull the stereo, the rims and tires and possibly junk the rest). Anyway thanks again!

 

I had an 04 explorer, great little suv.. terrible whine at 55-65 mph .
I pulled it apart not wanting to chance a temporary fix with different oils.
glad i did. the carrier bearing on passenger side was shot. the race and bearings were totally pitted and rough. the pinion bearing looked good and other side was good too.
I changed out all of them. put the heavier oil in that ford recommends now. very quiet now.
Biggest problem with these rears is the aluminum case. too much room for flex. ford never had any issues with the old 8.8 rears with cast case.
sometimes you shouldnt mess with success. my 2 cents

 

I forgot to mention. you dont need friction modifier if you dont have locker rear end. look at your tag on the rear. if it has an L in the ID tag..ie..
3L55, 3L75 then its a locker if it reads 3. 55 then its open rear and no need for modifier. be careful with your modifier too much and you will render your locker useless, too little and she will lockup on corners. I usually add like 4-6 ounces then drive it if she binds up then add another ounce, till she drives nice.

 

I have the original window sticker and it says that I have the 3.73 gears. Does that mean it's a locker? I have not looked at the tag, it's dark outside.

Now, is it true that Ford recommends changing the diff oil to a heavier grade, or is it just a rumor? If true, what grade should I get? Shorod, above, said it says SAE 75W-140 in the updated 2008 manual. Is that the heavier grade?

Thanks.

PS - I still haven't figured out how to get the new oil into the diff with the independent rear suspension. The arm is right in front of the fill hole and it's a pretty tight fit. I'm thinking of pumping it in there but I might not even be able to get the hose in, it's so close that the hose might pinch when at that angle. I'll look closer tomorrow.

 

older trucks were 80-w90 gear lube. New spec is 75- w140 synthetic, somewhat thicker. DOnt put anything thicker than that. The friction modifier is just that, to modify the oil in hopes of making a change in the gear whine. My axle does not have the LS rear end, but the modifier helps "modify" the oil and did help my slight whine. I always park the truck nose down hill when filling, so i can get a little extra oil in it.. You can get a 3/4 to 1/2 inch adaptor to put on your ratchet at Aoto Zone for a coupe dollars, or get a short 3/4 inch square rod and put a cresent wrench on it. There should be a couple inches clearance between the plug and the frame for adding oil. A small pump would help.