Very strange .......

The fluid stops flowing out in the feed hose,
and through the banjo bolt.

The system is now totally closed off inside the shock.

Relatively incompressable, the fluid brings the
upwardly moving wheel to a pretty quick stop.

The pressure rises inside the shock at a terrifically
fast rate, perhaps reaching 4,500 pounds per square
inch, in fractions of a second, as the wheel stops.

If the pressure in the shock is 4,500 PSI, the
pressure on the little piece of plastic
over the small hole is quite small.

Only 146 PSI.

(4,500 PSI x 0.032 inch square = 146 PSI)

However, the pressure is probably enough to
rupture the aluminum shock tube.

The hole forms, and pressure is released.

In the explosive rush of the fluid out the new hole,
the bit of plastic, propelled by the pressure in the system,
is blown out the new hole.

The outgoing fluid coats the right rear tire,
and the driving gets "interesting."

Thanks for tuning in, folks !
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I think also the point not to be missed is that
the root cause could be the wrong fluid added
to the power steering / hydraulic suspension
at some point.

That was why I was so careful to flush the system,
and to put ONLY the recomended SHELL DONAX TA
in when I finished............
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It may be that this is not the ultimate cause,
but is a contributing cause to an over-pressure
situation.

 

I may be mistaken, but I thought the "accumulator"
function was aslo to accomodate for an "overpressure"
situation within the shock body.

 

I agree

 

I agree.

Your thinking has been pretty clear,
all along on this.

I can only think that, for whatever reason,
the "bump" was more than the washers were able
to pass at that moment, and that the pressure "spiked"
between the piston and the banjo.

With the "saving grace" of the accumulator and backflow
system denied, the shock body ruptured.

You are, and have been,
offering great comments.

I remain open to suggestions.

 

Fred:

I attended your line of thinking while I was at lunch.

I wonder now if the "plastic band" disintegrated,
moved to the bottom area of the shock, and then
was "sucked up" to the piston area,
where it obscured the ports through the piston,
during the "heavy compression.".

Same effect.

Wrong diagnosis on my part.......

 

Well, maybe I am not mistaken, after all.

That is, I was mistaken about mistaken…..

There is no air inside this shock
(or, there was none when I opened it up)

a) The shock body has an inside diameter of 46mm.

b) The shock shaft has an outside diameter of 22mm.

c) The travel of the shaft is about 120mm.

d) The inside volume of the traveled portion of the shock body,
without the shaft, is about 200cc.

e) The same length of shock shaft displaces a volume of about 45cc.

f) The volume of fluid inside the shock body, at full compression,
and outside the shock shaft is 200cc - 45cc = 155cc.

g) If the shaft is all the way "up", (extended),than assume there is 200cc
of volume of fluid inside the shock body.

h) If the wheel is to rise, than the shock body must rise.

i) If the shock shaft remains attached to the car,
than the shaft must enter more deeply into the shock body.

j) If the shaft enters the shock body by some amount,
the volume available for fluid must be decreased by the
same amount as the volume of the shaft entering

k) If the captured fluid is not compressible, than it must be displaced.

l) Where does it go ?

m) If the "banjo" is open, the fluid may compress the "accumulater,"
and /or re-enter the supply system.

n) If the "banjo" is closed, than the fluid cannot escape.

o) The pressure will rise - in sort of a square wave function - until something fails.

p) Such, as in this case, the shock body.
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I can't find it in any literature.

Where is that valve ?

 

Correct.

I took a look at the portions of the service manual
quoted in post #87, and found this:

“The pressure in the principle gallery increases up to a maximum
of about 120 bar, over which a safety ball valve will open

NOTE: for brief instants in particular load conditions
it could reach as much as 140 bar.”

This should indicate that once 140 bar (about 2,000 pounds) the
safety valve opens and relieves excess pressure.

Therefore, if the sudden rise in pressure in the shock from
my "bump" exceeded 140 bar, than the valve should open,
and the extra pressure bled back "upstream" into the system.

I have to assume that the bump I hit was foreseeable by Ferrari,
and that the system was designed to accommodate just such a "bump."

Since the accumulators are designed to also mitigate "spikes" in the shock system,
they should also accept pressure from the "bump."

In the Ferrari 456 shock system, both accumulators seem to be in the same system,
so sudden pressure rises in one shock should transmit hydraulic
pressure rises from one shock to both accumulators, and to the other shock.

My assumption is that with this much “reserve” in the hydraulic system,
there would have been no “explosion” if the pressure “spike
could have been evenly transmitted throughout the system.

I find it hard to believe that both accumulators,
the safety valve, and the other shock could
have malfunctioned in a way that would allow
the right shock to "explode" without apparent
damage to any other part of the system.

However, the little piece of plastic
now makes better sense.

 

Been almost a month now, and the car
continues to provide much pleasure driving.

Found, as recommended on another thread,
that the "driving experience" is enhanced
leaving the transmission in 3rd while in town.

Car now has TUBI mufflers, and a much
more satisfying sound, especially
between 2,000 and 3,000 rpm.

Had to take a trip to Europe, and the schedule
worked out exactly wrong !

Arrived in Nice shortly after Monaco GP race,
thus missing the expected "Ferrari parade."

Went up to Geneva for a meeting at the Large Hadron Collider.
Couldn't get any work done, since the French power system
had a "total shutdown" that stopped everything.

The CERN brass were giving everybody the day off.

The LHC uses 10 Megawatts at full chat,
and that's a big draw !

Went through Switzerland and down into Italy.
Had to be back yesterday,
and so also missed the MotoGP race at Mugello.

Saw exactly NO Ferrari in France and Switzerland.

Got all the way from Como to the Italian Rivera before
I spotted a 360 in one of the frequent tunnels.
The approaching sound tipped me off as to what was coming.
Also was passed in a tunnel by my first personal sighting
of the new 458. Nice sounds.

Chatted briefly with a 360 owner at Cap Ferrat.

Only 3 Ferrari
loads of Mazarati.
Lots of Aston Martins.

One 1958 Edsel, and one
early Chrysler 300 "letter Car,"
both in Switzerland.

My rented diesel Ford econobox did not excite,
but got great mileage...

 

I was having trouble with some of the same thoughts.....

Then, I figured that any car can have improper-maintainance
problems. Once I committed to do the repairs in the right
way, and (more importantly) thinking I had the problem
figured out so that it would not re-appear, I was much
more happy with the car and the process.

After all, it's just a car.

Not nuclear science......

 

Been about a month now, and I have been able to drive the car
with no problems, and increasing confidence.

Checked the PS fluid, and found it (cold) below the dip stick,
and added about 1/4 liter,
which made it a little too full.

Realised that (palm to forehead here) that I probably should
have checked the level "hot."

Good excuse to drive the car a little hard, which I did.

Back in the garage, used an all-metal (think auto-zone)
turkey baster to draw the level down to the "just right" mark.

I am assuming that, with no apparent leaks, that the
slight low-level finding was the result of getting
all the "disolved" air out of the system.

Good as new ?

Hope so !

(Before-low)
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After- just right.
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OK:

Finally got a chance to take it out for a test,
and here's the "film at 11:00."

Turn up the volume........

http://www.youtube.com/watch?v=tU-EPRHuwg4

 

For those of you who have gotten this far:

Car has been running for 18 more months,
and has no running problems of any kind.

Suspension is perfect !

NO fluid loss !

Since this started, I aquired another 456
(Yes, I know - slow learner...) but a 6-speed.

AND, from Fchat's own SF, a BEAUTIFUL TDF Blue / tan
575M F-1.

The 456 6-speed - in a deal just concluded -
will be race-prepared in a shop for running
in Nevada open-road racing.

http://www.sscc.us/

I have a driver, who is a previous overall winner
in one of the Nevada open-road races.

HMmmmmm........
Now we need a navigator......

Reccomendations ?

Cheers,

Scott