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Kenny Z.
Kenny Z., Senior Master Tech
Category: Mercury
Satisfied Customers: 5524
Experience:  Mercury Senior Master Technician
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2002 Mercury Mountaineer: V6, AWD, 145,000 miles..complete stop

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I have a 2002 Mercury Mountaineer, V6, AWD, 145,000 miles. When i turn sharply to the left or right, while backing or going forward, the rear inside tire seems to want to turn as fast as the outside tire and will even make a squealing sound depending on the type of pavement I am on. I have to give it the gas in order to complete my turn, or the vehicle will come to a complete stop. I took it to a shop and the mechanic checked the rear differential and found the fluid was black and stinky. He drained it and refilled with 75W-140 and also put in an additive (KW-402508). He said I would need to put some miles on the vehicle before I would likely notice a difference. He said the clutches are probably bound up, but the new fluid and additive would hopefully free them up after a while. I only picked it up yesterday and found it is still as bad as before and am wondering if what he told me is correct? Is it likely the clutch/clutches in the differential will free up after some miles? Do you think this is even the problem? Today I found a service bulletin (TSB 04-24-20) that sounds like the solution to my problem, but I want to be sure the clutch pack in the rear differential IS the problem. There is no noise or popping sounds as described by a lot of other unhappy consumers.

I have also read numerous other similar complaints and solutions and it seems the other possible problem is the transfer case. I did change the oil in the TC myself a couple of weeks ago. The fluid that came out was not red, but a purple-lish milky color. I had just changed this fluid about nine months ago. I have also read where someone suggested you remove the front drive shaft and then drive the vehicle to see if the problem still exists. Is this something I should do? If the problem goes away with the front drive shaft removed, does this point to the viscous clutch in the TC? Any help/guidance will be much appreciated. We want to keep this vehicle, especially after all the money we have sunk into it, but we haven't yet addressed the rust problem on both sides above the running boards. This appears to be another Ford problem they can't afford to fix for the customer. The vehicle looks very nice with the doors shut, but when you open them, WOW! RUST galore, especially around the dog legs/under backdoor openings. Sorry this is so long.
Hello and thanks for your question.

When the viscous clutch fails, there will be noticeable front wheel hop on full lock turns at very low speed. If your not experiencing this then more than likely its the rear diff clutches. If you are unsure disconnecting the front shaft will definitely rule it out as a possibility. Changing the fluid and friction modifier will never help the rear clutches. Once they start to bind the only remedy is to replace the clutch packs.
Customer: replied 5 years ago.
Is disconnecting the front shaft something a novice can do? I have ramps and some tools. What tools would I need to remove the front shaft? I believe you are right on about the rear diff, but I just want to make sure 100% it is not the TC. Also, what is the approximate cost for a mechanic to replace the clutch packs? Is this something a novice can do, or should I leave that to the professionals?
Clutch packs definitely for a pro, to remove the front shaft torx 30 bolts in the front and 8MM for the rear, careful when removing the front so the cups don't fall off the u-joint.
Customer: replied 5 years ago.
"to remove the front shaft torx 30 bolts in the front and 8MM for the rear". Not sure I understand what you mean by "torx 30 bolts in the front". Also, what is the approximate cost for a mechanic to replace the clutch packs? Parts & Labor.
The front of the front drive shaft is held in by bolts that require a torx 30 socket to remove. The rear of the shaft is held in by 8 millimeter bolts which require an 8 millimeter socket to remove.

Price for replacing the rear clutch packs is around $800 at the dealer.
Customer: replied 5 years ago.
Ok, Kenny. Thanks for your help. I checked wikipedia for a torx socket and feel a little stupid now. I may have a T30 in the toolbox, but if not, Sears is not far away. I will leave the clutch packs alone, but I will take a look at the front shaft and see if I want to get into that myself. Sorry, it took so long to get back with you, but I have one last question. You mentioned in your first response, "When the viscous clutch fails, there will be noticeable front wheel hop on full lock turns at very low speed". Would this still be accurate for my Mountaineer, which is AWD? I don't have the option of turning it on or off.
Yes in fact its only applicable to the AWD mountaineer. The AWD is the only one with the viscous clutch, all the others are controlled by a shift motor and electric clutch. The clutch fails in the applied position keeping the front axle engaged which causes the hop.
Customer: replied 5 years ago.
Sounds good, but I have one last question. This time I mean it. I was checking online for a clutch pack, but the TSB I read said there were two different limited slip axles and i want to be certain I am ordering the right one. I believe, if I am reading the TSB correctly, my Mountaineer has the 8.8" limited slip rear axle? Is this correct, or should I call my local Ford dealer and give them my VIN# XXXXX confirm? I found a clutch pack at Tasco Ford in Rhode Island for $117.45. Does this sound like a good price, or do you know of somewhere else I can find one for less? Thanks again.
That is very cheap. The diff size is on a tag on the rear cover, if you can get me the tag info then I can tell you which one it has.
Customer: replied 5 years ago.
There were two numbers on the tag. Here they are....

S PM 503E
73 88 1D21
There are more numbers than that, they start right against the bolt head but this is enough its an 8.8.
Kenny Z. and other Mercury Specialists are ready to help you
Customer: replied 5 years ago.
Those are the only numbers that were on the small metal tag attached to the passenger side of the housing. I used a flashlight, even though it was daylight when I got under the vehicle, and was able to see everything. However, I didn't look for anyother numbers elsewhere. Thanks for your time. I should have submitted my questions to a long time ago. It would have saved me a lot of online time!
Your welcome.