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Thread: Aluminum driveshaft

  1. #1
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    Aluminum driveshaft

    I've searched and can't seem to find the answer. I've read about possible driveshaft virations in the Marauder, and the Aluminum MMX 'cure' Question is, is the stock Marauder driveshaft not the same as the Police Interceptor driveshaft?

  2. #2
    Brian Guest

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    MM Aluminum driveshaft is very similar to the Police drive shaft. The difference between the two is that MM has an added "Slip Yoke Damper". The damper is an added ring on the driveshaft tuned to absorb the same frequency as is produced by the the rear axle ring and pinion gear mesh frequency. It is there to lessen the amount of axle whine transmitted into the passenger compartment.

  3. #3
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    Thanks Brian. I'm guessing the aluminum driveshaft used in the Police Interceptor is no longer MMX. I know it was at least for a few years

  4. #4
    Brian Guest
    Correct. No MMX currently sold on CV Police. Aluminumin tubing.

  5. #5

    Metal Matrix Drive shaft

    I have been selling them for years, and they cure the problem most Mark8's have and as you know I had one made for the Marauder.





    - Drive shafts are balanced at a minimum of 6000 RPM
    - Drive shafts are balanced to under .25 oz - inches
    - Drive shaft run outs are to be with in .015
    - U Joint clearances are to be .002 0r less
    - Balance weights are fused welded to shaft tube
    - Drive shafts are rebalanced after welding
    - Drive shafts are manufactured with Dana Spicer parts

  6. #6
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    Interesting. Does the Marauder use the same transmission tailshaft as the Police Interceptor then?

  7. #7
    Brian Guest
    MM and CV Police Interceptor share a transmission tail extension housing, and related components. (The extension housing is longer than the retail CV/GM.)

  8. #8
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    Posted this yeaterday, but it isn't showing so here it is again

    I was given this number as being the Police Aluminum MMC driveshaft that was used in '99 and possibly '00.
    I don't know if it's still available, or the price if it is

    XW7Z-4602-AA MMC shaft

  9. #9
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    OK I think this thread answers some driveshaft questions, but does anyone know what the critical speed is for the interceptor driveshaft?

    Check out this link about critical speeds, great information

    Critical speeds link
    2 shoes and a nice pair of comfy socks

  10. #10
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    Mensrea;
    Perhaps you understand this scientific stuff, but I'm not sure I do. What I did read, kinda says that now I've upped my gear to 4:10, I should change the drive saft? Or, does it say that I must change the drive shaft?

    I asked Dennis about this a few weeks ago, and (without the science) he said that I should not need to change unless I plan on sustained high speeds, or, serious racing. This article leads me to believe that "high speed" for the OEM drive shaft, is 76 mph? I've been know to cruise toll roads at 80 or so, but rarely much higher, and for periods of two hours or more. Do you think I should upgrade the drive shaft?

  11. #11
    The Marauder was tested at 140 mph if you have the money and are planning on high speed I would go with the Metal Matrix Drive shaft, if not stock is fine unless you are getting high speed vibrartion Logan said it cured his.

  12. #12
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    I am going to wait for someone with more expertise to respond to this request. I know that I experienced driveline vibration with the stock shaft at certain speeds I switched my shaft and don't seem to notice the same vibration.

    There was a person from Ford on here that responded to some comments in the Sean Hyland forum, but that thread is gone.

    I have asked numerous people about the MMC drive shaft used in the Police Interceptor. It uses the same tail shaft housing that we have in the Marauder, and is much less than custom drive shaft.

    You can pick one up from ford for 200. I just don't know that much about the critical speed of it. I do know that the reason some panther platform people were hesitant to use it previously was that you had to change the tail shaft housing, which you don't have to do with the Marauder.
    2 shoes and a nice pair of comfy socks

  13. #13
    Every rotating object has a “critical” speed or
    resonant speed, which is a function of its design,
    mass and stiffness. This is when the driveshaft is
    whipping in the middle, rather than spinning on a true
    centerline. For a driveshaft, this is also called
    “first bending mode”, indicating the shaft actually
    bows out into a boomerang shape (on a micro-scale).
    This first mode bending speed is usually referred to
    in a driveshaft frequency.

    What it does –
    The energy stored and released through the deflection
    of the driveshaft through the resonance creates
    lateral and vertical accelerations of >10g at the
    problem frequency, which results in broken
    transmission extension housings, cases and causes
    moderate to severe vibration at highway speeds (> 70
    mph), particularly with axle ratios numerically higher
    than 3.27:1. This energy release, when compounded by
    excessive driveshaft imbalance (some is good, too much
    or too little is not), companion flange run
    out/imbalance and excessive driveline angles provides
    the driver with excessive vibration and boom and
    tortures the driver and driveline components in
    general.

    Because of this, most vehicles have a speed limiter to
    prevent from entering this mode and causing damage to
    the driveline.

    Some detail –
    As mentioned above, the driveshaft rotates at a
    certain speed based on rear axle ratio; tire size and
    road speed, but is independent of engine speed (unless
    you have a vehicle such as a Porsche 944 or C5
    Corvette which utilize torque tubes and transaxles, in
    which case the driveshaft turns at engine speed).

    The factors governing driveshaft critical speed
    include its material properties (i.e., Bulk Modulus of
    Elasticity which is roughly analogous to material
    stiffness), diameter, and length and to a lesser
    degree, wall thickness.

    The only factor you can really modify to affect
    critical speed is material choice. Length is
    package-dictated, and diameter is usually constrained
    by driveline tunnel space as well. The answer then
    becomes a bit simpler – replace your steel shaft with
    an aluminum or MMC (metal matrix composite) shaft.
    Both offer reduced weight, which is key in this
    frequency range. MMC offers the additional bonus of
    additional damping and stiffness over a typical
    aluminum alloy.

    As mentioned above, at the frequencies in question, a
    change in rotational mass has a greater impact on
    resonant frequency than a change in stiffness does,
    partly since it is easier to reduce mass than increase
    stiffness (adding stiffness almost invariably means
    adding mass -- a vicious circle), but particularly
    since resonant frequency is equal to the sqrt (k/m),
    where m is mass and k is stiffness. Here m is a
    stronger function being the in the denominator of a
    square root. So you can see that as “m” gets smaller,
    the resonant frequency “f” gets much bigger.

    The use of an aluminum shaft provides a dual purpose –
    increasing critical speed out of the operating range
    AND directly reduces the rotational forces since those
    rotational forces are governed by:

    F = mr w**2
    Where w is rotation speed, m is the mass and r is the
    radius at which it is spinning.

    This means that a 50% reduction in rotational mass
    results in 50% less rotational force. So, when a
    driveshaft rotates out of true, due to run out of the
    shaft itself or due to trans output shaft or axle
    companion flange run out, the reduced mass * the
    radius of gyration (i.e., run out) product is smaller
    than for the same conditions with a steel shaft.

    This becomes important not only at critical speed, but
    at more normal operational speeds where the effects of
    run out and mass imbalance are more evident than those
    of resonance:

    For a typical Fox or SN95 Mustang, driveline critical
    speed is around 95-100 Hz. Using stock tires we have
    the following:

    225-60R15, 225-55R16, 245-45R17 all rotate at 812-820
    revs/mile at 60 mph.

    This give is 13.5 Hz wheel frequency at 60 mph, and
    assuming a 3.27 axle, we then have:

    812/60*3.27 or 44.25 Hz , driveline frequency.

    So, 100/44.25*60 yields a driveline critical VEHICLE
    speed of 135 mph. A good rule of thumb states that
    the objectionable driveline forces will start becoming
    significant at 70% of resonant frequency, so for the
    case of the 3.27 axle, the boom and vibration may be
    felt beginning at 95 mph.

    Typically, 3.27 axles don’t provide the driver with
    much to complain about; it is 3.73 and above which
    create the concerns. Using a 3.73, we find that

    13.53*3.73 gives 50.5 Hz wheel frequency at 60 mph
    (substantially higher than the 3.27)

    And the critical VEHICLE speed then becomes

    100/50.5*60 or 119 mph.

    Taking 70% of 119 mph equals 83 mph, certainly a speed
    at which some Mustang drivers experience occasionally.

    For a 4.10 axle, the “70% speed” is 76 mph!

    Compounding this problem are factors like transmission
    output shaft run out, imbalances and run outs from
    components such as the reverse sun gear, driveshaft,
    companion flange and pinion pitch line run out (a
    torque induced run out created when the pinion tries
    to crawl up the face of the ring gear involutes).

    Combine these factors and the already marginal NVH
    resulting from proximity to 1st bending (critical
    speed) and the NVH becomes absolutely agricultural.

    The aluminum shaft minimizes the contribution from
    companion flange run out and the driveshaft’s own run
    out, directly due the lower mass. The pinion is free
    to pitch +/- 20 degrees and adding in any run outs of
    the companion flange or driveshaft at the pinion end
    results in the driveshaft mass having a large
    eccentric path to wobble about. It is this path times
    the mass of the driveshaft, which gives the
    characteristic boom and vibration at highway speeds.

    Thus, as Newton predicted, as mass decreases so will
    the forces. That is why an aluminum shaft is your
    friend when coupled to 3.73s.

    One side note: that great big mass on your pinion
    nose, fondly named by driveline engineers after the
    appendage on a male moose, is tuned to 45 Hz, the
    frequency at which the 2nd order forces created by
    u-joints as they rotate, force the pinion to bounce or
    pitch up and down and shake you by the seat of your
    pants and create an uncomfortable boom in the car.
    Once again run outs and imbalances will modulate this
    2nd order driveline phenomenon to make it worse, so
    the moral is, LEAVE THE MOOSEB-, uh, DAMPER ON the
    pinion nose!

    Another item: you CAN expect more axle noise when
    using an aluminum shaft however, which does not
    necessarily mean the pinion depth or side shims are
    incorrect, or that the gear cutting process is flawed.
    It just means that the aluminum shaft is more willing
    to “bend” circumferentially, torsionally and in a
    double hump (2nd bending) much more easily than a
    steel shaft.

    Recall my prior statements at the very beginning about
    aluminum stiffness vs. steel? Picture a piece of
    sheet metal ducting. Bend it and it makes a WA-WA
    sound. That is pretty much what a driveshaft does,
    but at a much higher frequency – higher than even the
    dreaded “critical speed” of 100 Hz.

    Axle noise will occur from about 350 Hz all the way
    through 500 Hz, sometimes even higher than that. The
    energy comes from the teeth meshing at the pinion/ring
    gear interface. This energy is transmitted to the
    driveshaft (and suspension components) and makes them
    deflect in the same sense as a piece of sheet metal
    goes WA-WA. Aluminum is less stiff than steel and
    takes less energy to deflect it, so it is far more
    inclined to make your axle go WOOOOO as you drive down
    the road at 45-70 mph.

    Assuming again a 3.73 axle ratio, which has 11 teeth
    on the pinion and 41 on the ring gear, the axle noise
    frequency is calculated as (at 45-70 mph):

    815/60*3.73*11 or 557 Hz at 60 mph.

    This means the WOOO you hear at 45 mph is about 418 Hz
    and the WEEEEEE you hear at 70 mph is way up there at
    650 Hz. You can’t SEE the driveshaft is bending and
    breathing and twisting, but it is telling you that
    precisely that is occurring.

  14. #14
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    Dennis is that different than the TCCOA article, which I linked above???? Looks identical to me
    Last edited by mensrea; 12-03-2002 at 07:42 AM.
    2 shoes and a nice pair of comfy socks

  15. #15
    Yes, I did not see the link, so if you have allready reviewed it, what else would you like answered, the bottom line is if you have doubts buy the the Metal Matrix drive shaft. I believe he states this in several places, Since I talk to him every day I was just trying to help as I always do, we have talked about this alot, again the critical speed will vary with gear ratio, since most owners here are using the 4:10's we still see no absolute need for the MMDS, LOL here I am trying to talk people out of buying something I had designed for the Marauder, I sell three or more a month for the Mark 8 because of vibration that starts in the 80 MPH range. In your application I would for sure use one since you have increased RWHP and torque. But I will see if I can get the critical speed for you.


    Dennis

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