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Thread: Can someone explain how haldex AWD works?

  1. #1
    Join Date
    Jun 2018
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    Default Can someone explain how haldex AWD works?

    We just replaced a howling rear diff on an 04 xc70. Now after getting rid of all the network issues (here's that: http://www.volvoxc.com/forums/showth...-s-how-it-went )

    We are at a loss as to when and how haldex works. When we got the car and found the issue on jack stands, all 4 wheels turned.

    Now only the fronts spin. On dirt and pavement, in the air, only front wheels turn.

    I took my car out, and same thing 2 wheel peel. Mine has not been worked on, and they both have no messages on the dash other than SRS.

    Ugh, someone explain the ins and outs on haldex?

    How do I know if and when the AWD works???

  2. #2
    Join Date
    Dec 2009
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    GA
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    1,156

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    Quote Originally Posted by Hamfist View Post
    and they both have no messages on the dash other than SRS.

    How do I know if and when the AWD works???
    DEM codes will not cause a check engine light (they don't consider it emission related) or any indication on the dash


    The DEM tells the haldex clutch to engage (with hydraulic pressure generated from an electric pump that goes bad) when the front wheels spin faster than the rears. By the way when the pump goes bad sometimes it fries the DEM. There are helpful Diagnostic flow charts at Xemodex.com

    https://xemodex.com/us/knowledgebase/dem-flow-chart/

    First step would be to scan the car with a scan tool capable of talking to the DEM. (VIDA will give the most info) And go from here.
    Last edited by hoonk; 10-09-2018 at 06:14 PM. Reason: spelling

  3. #3
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    Quote Originally Posted by hoonk View Post
    DEM codes will not cause a check engine light (they don't consider it emission related) or any indication on the dash


    The DEM tells the haldex clutch to engage (with hydraulic pressure generated from an electric pump that goes bad) when the front wheels spin faster than the rears. By the way when the pump goes bad sometimes it fries the DEM. There are helpful Diagnostic flow charts at Xemodex.com

    https://xemodex.com/us/knowledgebase/dem-flow-chart/

    First step would be to scan the car when a scan tool capable of talking to the DEM. (VIDA will give the most info) And go from here.

    Blargh, both might be bad!! Sigh... Gotta get my vida

  4. #4
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    Quote Originally Posted by Hamfist View Post
    Blargh, both might be bad!! Sigh... Gotta get my vida
    Scanned, (other thread) and found my brake pedal position switch bad, replaced cleared codes and test drive. No codes returned, still spins fronts.

    No codes in Dem and no communication faults, DEM shows green and communicating.

    Next idea?

  5. #5
    Join Date
    Mar 2008
    Location
    Western Head, Nova Scotia
    Posts
    3,069

    Default

    Sounds like a striped bevel gear collar especially since you aren't see codes (VIDA scan?).

    Good Luck,

    Bill
    Western Head, NS CDN

    '05 V70R (Magic Blue)-119K mi to-date
    '05 XC70 (Lava Sand)-290K kms to-date
    '02 V70XC-gone @393K kms
    '98 V70-gone @390k kms
    '91 744GL-killed by son @ 220K kms
    '96 854R (Red)-real CDN-spec 5-speed R - gone @270k kms
    '90 744T w/Turbo Plus-killed by son @260K mi
    '78 245-killed by wife @166K mi
    '76 265-gas hog gone
    And other misc. Euro stuff

  6. #6
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    Jun 2018
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    Quote Originally Posted by billr99 View Post
    Sounds like a striped bevel gear collar especially since you aren't see codes (VIDA scan?).

    Good Luck,

    Bill
    Yeah I hear no crunching or any other driveline noise, car is super quiet. However in turns I hear a groaning, like a driveline binding in a 4x4 by the firewall. Guess I gotta get the car in the air and see if the propshaft spins.

    Good news is I have an extra anglegear in the shop from a previous parts car.

    Does anyone know how to diagnose if it's the angle gear or the sleeve prior to removal?

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