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2000 Mountaineer - Whine on acceleration - Quiet as a mouse on deceler

I had the same issue. I bought a bearing kit for the rebuild of my rear diff. and it worked out beautiful! My ring and pinion were in great shape but the pinion bearings were scored. Replaced all of the bearings, refilled with Royal Purple with the Ford Friction Modifier and it is PERFECT!
Glocker, thanks. This seems to be the consensus of the forum.
 



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@pjfsail If you compare Ford's recommended lubricant/oil specs over time (say 1995-2001) you will find many of them changed. This is not because the parts requiring lubrication have changed, but because better lubricants were developed. In some instances the old oils are not even available anymore because they are superseded by the newer oils. For example Mercon ATF was later superseded by Mercon V. A 1995 owner's manual my say to use Mercon in the transmission, but Mercon V is the current spec. Similarly for your rear diff, current recommended spec is 75W140 full synthetic hypoid gear oil (with Motorcraft friction modifier if LSD) but older vehicles might have been spec'ed for 80W90 conventional hypoid gear oil. By going by the current spec you use lubricants which offer the best protection. You don't gain anything by using the older spec lubricants (assuming they still available).

The upside is better protection against wear and usually increased change intervals. The downside is the synthetic lubricants cost more. If the older products are still available the choice is yours.
Koda2000, thanks so much. This is exactly the information I was looking for. I wanted and was looking for expert information from experts, this is why I joined the forum. The gear oils and the modifier were the issues for me, what went with what. Now I can be assured to use 75w140 full synthetic hypoid oil with the Motorcraft friction modifier. Being a mechanic myself but not in the automotive field I am fully aware how specs can change overtime and who knows best but the mechanic expert in the field. Thanks again for the information.
 






@pjfsail
Whine on acceleration only is almost certainly originating with the ring and pinion. Transmission pumps work at constant load, more or less, and have nothing to do with whether power is being transmitted or not. Pinion bearings which are bad can make lots of whining noise, but that noise is unaffected by transmission of power, IOW, acceleration or deceleration. Pinion bearings badly worn WILL allow misalignment of the gears, and CAN cause whine upon acceleration, because the forces trying to pry the gear teeth apart are high when accelerating, but very low when decelerating.

First order of the day would be to inspect the ring gear teeth. If shiny and bright, no scoring, galling, or dull-looking appearance, pinion bearings OR differential side bearings would be needed. imp
I pulled the cover on the rear differential and did inspect the ring gear and pinion.
@pjfsail
Whine on acceleration only is almost certainly originating with the ring and pinion. Transmission pumps work at constant load, more or less, and have nothing to do with whether power is being transmitted or not. Pinion bearings which are bad can make lots of whining noise, but that noise is unaffected by transmission of power, IOW, acceleration or deceleration. Pinion bearings badly worn WILL allow misalignment of the gears, and CAN cause whine upon acceleration, because the forces trying to pry the gear teeth apart are high when accelerating, but very low when decelerating.

First order of the day would be to inspect the ring gear teeth. If shiny and bright, no scoring, galling, or dull-looking appearance, pinion bearings OR differential side bearings would be needed. imp
 






I pulled the cover and inspected the ring gear and pinion and the backlash. I didn't see anything unusual and, like you, are beginning to suspect the differential could use a new set of bearings.
 






Look, you should use 75W140 full synthetic hypoid gear oil and with limited slip you should also use the Motorcraft friction modifier. Period.

The friction modifier prevents the LSD clutches from chattering. IDK if the friction modifier would be required with a non synthetic gear oil and I don't feel like researching it for you. You can Google this as well as I can.
koda2000, turns out you don't have to research it for me. I got the answer I need from and expert on the forum. Thanks for your input.
 






Hello pjfsail, I have a question that is not necessarily related to your whine, but could point to an impending problem. Does your Mountaineer have a 5.0L V-8 engine? If so, you have AWD and the Borg Warner 4404 single speed transfer case. You mentioned the transfer case oil was overful and black. That could be an indication that the viscous coupling has failed inside. What did you refill the transfer case with? Manual calls for MERCON ATF, not the same MERCON V that the 4R70W transmission takes.
Might be worth changing the transfer case fluid a couple of times with store brand Dexron III/Mercon ATF and see if it clears up.
That will do nothing for you if the viscous coupling has failed, but fresh fluid will be good if it hasn't.
How will I know, or is there at know if the viscous coupling has failed? The excess fluid would have to come from the transmission which requiries MERCON V and the transfer case requires MERCON ATF (without the V. If the transfer case was contaminated for an extended period I'm sure that is not good for the coupling either.
 






Hello pjfsail, I have a question that is not necessarily related to your whine, but could point to an impending problem. Does your Mountaineer have a 5.0L V-8 engine? If so, you have AWD and the Borg Warner 4404 single speed transfer case. You mentioned the transfer case oil was overful and black. That could be an indication that the viscous coupling has failed inside. What did you refill the transfer case with? Manual calls for MERCON ATF, not the same MERCON V that the 4R70W transmission takes.
Might be worth changing the transfer case fluid a couple of times with store brand Dexron III/Mercon ATF and see if it clears up.
That will do nothing for you if the viscous coupling has failed, but fresh fluid will be good if it hasn't.
How will I know, or is there at know if the viscous coupling has failed? The excess fluid would have to come from the transmission which requiries MERCON V and the transfer case requires MERCON ATF (without the V. If the transfer case was contaminated
Use a good synthetic 85w-140 gear oil, if that's what the tag on the case says, and also add the friction modifier to it. The friction modifier is what is required for limited-slip rear ends and allows the clutch pack to work correctly. I have a 1999 5.0 Explorer and it uses 75w-140, with added friction modifier as well, but the grades could have changed the next year.

If you're doing the front axle as well, it should use 80w-90 axle lube.[/QUOT
for an extended period I'm sure that is not good for the coupling either.
I was also thinking the same...

BUT NOTE: For this to be the case (bad pump) when the engine is running, and the Ex is standing still, the pump should still whine both in Park as well as Neutral.

To add - based on that there is no mention of the FRONT DIFF in your original post, I will add the following observation...

On 2nd Generation 4X4 Explorers/Mountaineers, the FRONT DIFFERENTIAL is the one that usually doesn't get serviced because the front cover can't be EASILY removed. All sorts of stuff is in the way that prevents the front diff cover from coming off short of unbolting & lowering the entire front axle housing - a really BIG job and something the 99 percentile will not do.

Without removing the front cover, to drain and fill the front diff, you have to do BOTH operations through the fill hole with first a suction pump. and then with a fill pump. In this case, the 80 percentile will not do this, it's about a two hour operation with a hand pump... I've done it this way every 50,000 miles and it's a PITA (but a necessary PITA).

Best time for this is during the summer as it's easier to move the high viscosity fluids.

Diff Fluid: I use Redline Synthetic or Mobil Synthetic 75-140 front & rear with no modifiers.
One thing I'm still confused about and would like to understand. When you use Redline Synthetic or Mobil Synthetic 75w -140 YOU DO NOT USE MODIFIERS. There must be a reason you don't use modifiers. 1) There are already modifiers in these brands. 2) You choose not to use a modifier when you use these oils based on your experience using these brands of synthetic gear oils. I hope no one takes offense at my questions. Hey, I'm an old guy, I've never used synthetic oils. I'm looking for good solid sound information so I can feel informed and up to date on at least one aspect of my new adventure with my Mountaineer (I love it)
 






Use the modifier no matter what
It's like five bucks better safe than sorry imo
 












Clutch disks in the diff for the limited slip
Or it will feel notchey around coroners when the clutch disks are ment to slip the addictive will let it slip smoothly
The cost is not the issue with me. I have two bottles of it. I want to know WHY.
 






The cost is not the issue with me. I have two bottles of it. I want to know WHY.
@pjfsail
For the reason @donalds says, the modifier allows the clutch discs to rotate against each other smoothly. Modifier has no effect upon gear whine, which originates from the gear teeth, not the clutch plates.

Transmission fluid CAN leak past the transmission output shaft seal. However, it is very unlikely for it to enter the Transfer Case for two reasons: the T Case has it's own seal on it's input shaft, which is spline-coupled to the transmission output shaft, and, the surface between the output shaft adaptor which accepts the bolting=up of the T Case has a "weep" groove, which allows leaked fluid from the transmission seal to escape and puddle under the vehicle. imp
 












@pjfsail
For the reason @donalds says, the modifier allows the clutch discs to rotate against each other smoothly. Modifier has no effect upon gear whine, which originates from the gear teeth, not the clutch plates.

Transmission fluid CAN leak past the transmission output shaft seal. However, it is very unlikely for it to enter the Transfer Case for two reasons: the T Case has it's own seal on it's input shaft, which is spline-coupled to the transmission output shaft, and, the surface between the output shaft adaptor which accepts the bolting=up of the T Case has a "weep" groove, which allows leaked fluid from the transmission seal to escape and puddle under the vehicle. imp
Thanks so much for taking the time to explain the information I was looking for. Joining this forum is one of the best things I have done in a long time. I truly appreciate everyone's input. What you have given me is specific information what oil I need in my rear differential, ideas of what to look for to eliminate the whine, and a good feeling about where to go for the questions I will have on my newly acquired 2000 Mercury Mountaineer. (love this truck)
 






@pjfsail
For the reason @donalds says, the modifier allows the clutch discs to rotate against each other smoothly. Modifier has no effect upon gear whine, which originates from the gear teeth, not the clutch plates.

Transmission fluid CAN leak past the transmission output shaft seal. However, it is very unlikely for it to enter the Transfer Case for two reasons: the T Case has it's own seal on it's input shaft, which is spline-coupled to the transmission output shaft, and, the surface between the output shaft adaptor which accepts the bolting=up of the T Case has a "weep" groove, which allows leaked fluid from the transmission seal to escape and puddle under the vehicle. imp
Imp, thanks for your input. With your detailed explanation of how the rear of the transmission is sealed between it and the transfer case What follows is hard to explain. When I went to drain the transfer case I removed the fill plug, not the drain plug. The purpose of me doing this was to see if the transfer case was full or low on fluid. I didn't want to drain it without knowing the fluid level. I was surprised when fluid came gushing out. It was definitely over full. Of course, I did not measure the amount as I was not ready for it to be overfull. I'm the kind of guy who is always curious about EVERYTHING. How did the oil get there? What affect did the overfilled transfer case have on the viscous coupling? I realize that the answers to these might not be possible it doesn't prevent my mind from asking them.
 






How will I know, or is there at know if the viscous coupling has failed? The excess fluid would have to come from the transmission which requiries MERCON V and the transfer case requires MERCON ATF (without the V. If the transfer case was contaminated


One thing I'm still confused about and would like to understand. When you use Redline Synthetic or Mobil Synthetic 75w -140 YOU DO NOT USE MODIFIERS. There must be a reason you don't use modifiers. 1) There are already modifiers in these brands. 2) You choose not to use a modifier when you use these oils based on your experience using these brands of synthetic gear oils. I hope no one takes offense at my questions. Hey, I'm an old guy, I've never used synthetic oils. I'm looking for good solid sound information so I can feel informed and up to date on at least one aspect of my new adventure with my Mountaineer (I love it)
I found the answer I was looking for. It turns out the Synthetic Gear lube you mention are all 3 have the friction modifiers built in to them. No additional modifiers are necessary.
Hello pjfsail, I have a question that is not necessarily related to your whine, but could point to an impending problem. Does your Mountaineer have a 5.0L V-8 engine? If so, you have AWD and the Borg Warner 4404 single speed transfer case. You mentioned the transfer case oil was overful and black. That could be an indication that the viscous coupling has failed inside. What did you refill the transfer case with? Manual calls for MERCON ATF, not the same MERCON V that the 4R70W transmission takes.
Might be worth changing the transfer case fluid a couple of times with store brand Dexron III/Mercon ATF and see if it clears up.
That will do nothing for you if the viscous coupling has failed, but fresh fluid will be good if it hasn't.
Skpyle, I haven't refilled it but I know now not to use V but to use Mercon ATF. I have quart bottles of MERCON ATF ready to pump into the transfer case. When I get the Mountaineeer finished with it's oil change and up and running I will change the transfer case fluid a number of times like you suggest. Thanks for your input.
 






If that is an AWD 302 truck, the transfer case shouldn't ever have dark fluid come out of it. That is an indication that the tires have been mismatched for a while, at some time prior. The viscous clutch builds heat when the tires don't turn the exact same amount front to back.

So for any AWD, be very sure that the tires do match front to rear, in total(each pair) diameter. If not the AWD TC will in the long run fail, usually locking up which will hard bind the front tires/diff/CV joints.

Some high end synthetic brands of gear oil won't need a friction modifier for an LS rear. But old used clutches often don't need it either for any fluid. Use it for sure if you have it, and note many aftermarket gear oils are cheaper than Motorcraft brand. It's near $25 a quart at Ford, and Amsoil is now up to about $15 per. It takes less than three quarts for the rear, and under two in front.

Hopefully your ring and pinion gears are still good, the bearings(other than pinion) aren't that bad to replace. I do the axle bearings and seals often at the same time as gear oil, I like about 50-75k miles depending on usage. Those are the weakest links, gear oil, axle bearings and seals. Check your u-joints also, those can whine sometimes and 200k is a good level to reach before replacing those.
 






Whine on acceleration is most likely bad carrier bearings, and noise created between gears when separated from torque.

The trans has a drain in the tail housing, allowing fluids into the transfer case. I have to plug that drain after the tcase is removed, when I pull the trans, so it doesn't make a mess. Beats having to work around a drain pan.
 






Imp, thanks for your input. With your detailed explanation of how the rear of the transmission is sealed between it and the transfer case What follows is hard to explain. When I went to drain the transfer case I removed the fill plug, not the drain plug. The purpose of me doing this was to see if the transfer case was full or low on fluid. I didn't want to drain it without knowing the fluid level. I was surprised when fluid came gushing out. It was definitely over full. Of course, I did not measure the amount as I was not ready for it to be overfull. I'm the kind of guy who is always curious about EVERYTHING. How did the oil get there? What affect did the overfilled transfer case have on the viscous coupling? I realize that the answers to these might not be possible it doesn't prevent my mind from asking them.
@pjfsail
A gross overfill should cause puking out of the fluid through the vent. If the fluid came from the transmission, the transmission should have been low on oil. Overfill on an AWD likely hurts nothing. However, blackening of the fluid surely does, as mentioned by @CDW6212R . Mismatched tires will surely tax the viscous coupling, causing overheating. There are no clutch-like parts in it, strictly a "baby torque converter" without torque multiplication. imp
 






Whine on acceleration is most likely bad carrier bearings, and noise created between gears when separated from torque.

The trans has a drain in the tail housing, allowing fluids into the transfer case. I have to plug that drain after the tcase is removed, when I pull the trans, so it doesn't make a mess. Beats having to work around a drain pan.
@gmanpaint
That's different than gen III. The "lip" on my '04 trans. output adaptor has a groove to relieve any seal leakage to the outside. Why they put a gasket there, I suppose, was to keep out as much dust as possible. The T-case front seal is double-lipped, meaning the outside lip faces forward, to prevent possibility of fluid getting past the inside lip, which faces rearward, and seals the T-case. imp
 



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The front of the 2nd gen transfer cases does have a good seal, and the short trans tail housing will let excess fluid into that space. But an overfill from the trans would have to fill that short housing quite a bit to produce fluid at the TC front seal. I think the seal will stop virtually all fluid come getting in. The trans would have to be very overfilled to put enough at the TC to get any in. The trans overflow vent would be well used before anything got into the TC. It's pretty bad to overfill a trans that much, I doubt that happened but didn't hurt the trans enough that it all got taken apart.

I'll bet trans hasn't been hurt, and the AWD TC is like all others, bad fluid suggests it had bad tires on it. The question is how long was the truck run with mismatched tires. I got my 98 with 158k on it, and black TC fluid. I changed it then, and about five months later, still black, and about nine months later, still black.

At around 198k last year, I began to feel a binding in the front while turning. I didn't immediately conclude it was a bad TC. I had new front control arms to put on, and saw a barely torn CV axle a week before. So I replaced the axle and inspected, nothing to see. I got two days off and did the four CA's, driving to the alignment it had major popping backing out and driving straight. Then I decided it was the front diff, I was right, came home from the alignment and swapped a used one in. That "fixed" the bad popping, the old diff/pinion could move a bunch side to side. The binding also was not gone, so after a bit of driving to test, I removed the front driveshaft. Bingo, symptoms gone, the AWD TC had basically locked up and took out the front diff. I've driven it that way since then, gladly the TC is still transferring power. I've read that sometimes when the AWD fails, there's no movement.
 






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