Aluminum driveshaft

[RCSignals]

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?

[Brian]

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.

[RCSignals]

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

[Brian]

Correct. No MMX currently sold on CV Police. Aluminumin tubing.

[Dennis Reinhart]

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.

http://web.iwebcenters.com/reinhartautomotive/images/metalmatrixdriveshaft.jpg



- 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

[RCSignals]

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

[Brian]

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

[RCSignals]

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

[mensrea]

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 (http://www.tccoa.com/articles/tranny/transmission/page17.shtml)

[SergntMac]

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?

[Dennis Reinhart]

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.

[mensrea]

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.

[Dennis Reinhart]

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.

[mensrea]

Dennis is that different than the TCCOA article, which I linked above???? Looks identical to me

[Dennis Reinhart]

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

[mensrea]

Dennis, I wasn't sure if there was a newer version of the "bible" out there that I didn't see... Also, I have one in my car, but was searching around on crownvic.net and saw that there was a lot of discussion about the Interceptor driveshaft, and got curious.

I really am trying to find out if the MMC driveshafts from the interceptors would be as effective as the Dynotech one.

And I did feel vibration above 85... I wonder if it is just a couple of the cars

[Mikeenh]

Dennis,
WOW! :eek: