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Mercury Mountaineer 2003 Transfer Case Problem

February 3, 2014 - Author: BartBarton - 10 Comments

Mercury Mountaineer 2003 Transfer Case Is Viscous Coupler Problem?

I have a Mercury Mountaineer 2003 with the 4.6L engine with automatic transmission and 4WD.


This vehicle has 125000 miles and has been used to pull a 25′ trailer over bw4410the last 5 summers.  When turning the vehicle on the asphalt it feels like the front tires are pawing, at first I thought that maybe it was the rear differential.  A few days ago it was stuck in the snow and the rear end was not locked up.  I have inspected both the front and rear differential with the covers off and all looks good.  I suspect the viscous clutch is the issue.


You have the BW4410 transfer case we agree based on your description the viscous coupler is defective and needs to be replaced.  While you have the unit apart we suggest you check the drive chain for excessive wear or stretch.  The parts you will need are:

  • Viscous Coupler part number MWT4400-625-001 your cost is $329.00
  • Seal kit your cost $15.00 plus S&H.

Make sure all of the tires are the same diameter and pressure, this is the #1 cause of viscous coupler failure.

For information on replacement transfer cases see our site.

Categories: Uncategorized

Discussion (10 Comments)

  1. by martin obrien

    same problem when turning front wheels it feels like thier pawing.Can I take the front drive shaft off and drive it that way. Is it difficult to remove (2003 mountaineer).

    • Sounds like a bad viscous coupler. This is inside the transfer case it is what locks up to actuate the front wheels in AWD. When they go bad they don’t release all the way and cause binding like you are experiencing . You would have to remove the transfer case and disassemble it to repair. Part number of the viscous coupler is 4400-625-001 cost $489.05 seal kit K100911 $20.00 plus whatever else you find inside that needs to be replaced. You could purchase a rebuilt transfer case PFU429-4 cost $1000.00. Typically you should not drive this truck with the front shaft out because it will damage the viscous coupler . If you have any other questions please call toll free 1-800-444-0755.

  2. by John White

    I have a Ford Explorer 2004 with the 4.6L engine with automatic transmission and AWD VIN 1FMZU84W24UB21762 with a BW4410 transfer case that has a bad viscous coupler. Could you help me save some money on a replacement. I noticed on your blog that your price jumped $160 from 2014 to 2015. Hopefully that was not true because that really pushes my pocket. The car has 187000 miles and it not worth putting a lot into it. Could you send me the price for the coupler and gasket kit please. Thanks

    • Hello,
      Thanks for your question! Here are the parts that our expert recommends, Rebuilt Coupler 4400-625-001R $532.00 plus $150.00 core seal kit K100911 $20.00.
      If you would like to order please call toll free 800-444-0755 and ask for James he will be able to help you out.

  3. I need a PFU429-4 transfer case. Your recent comments with Courtney on Mercury Mountaineer 2003 Transfer Case Problem…your reply was You could purchase a rebuilt transfer case PFU429-4 cost $1000.00. I can come in person next week (7-11-16 to 7-15-16) to give you my core and pick up the rebuilt for $1000.00

    • If you give James a call at Proven Force 800-444-0755 he can help you and make sure that he has the part ready for you and go over any other detail necessary.

  4. by paul

    I have a 2002 Mountaineer 4.6 automatic, and it does the pawing that feels like the Viscous coupler. I swapped out the transfer case with a junkyard unit, and found that both are not locked up and the problem persists. The tires are all the same, so that is not the issue. The only other potential issue I have seen is that a front differential mount on the drivers side looks bad. What else could be causing the binding? Truck is way to nice to give up on!

    • Hi there I got both of our experts to chime in on your question here is what they had to say, Maybe the junkyard unit had a bad viscous also? I wouldn’t think a diff mount would do anything but make some noise. And my second expert said, Yes I agree, not knowing the history of the used transfer case I would come to the same conclusion of a bad viscous coupling in both units.

  5. by paul

    that was my first thought as well. The viscous is not locked up on the first unit though. You can spin the front coupling when the rear shaft coupling is held stationary. I thought the differential mouont as it would make the power train alignment off whenever there was any torque applied?
    Is there any way other way to test the viscous?

  6. by paul

    Is there a way to bench test the transfer case to know if the viscous is bad?

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