Very strange .......

Remove the damper washers under the nut.
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The main part remains.
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Whole lots more UNDER
the big guy. I am NOT
able to put this back together !
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A closer look at the main guy.

So far, everything is neat and clean,
no signs of damage, and NO debris
inside the shock.
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Just an additional information about the system:
The pump is of the twin type, one part used for the power steering at a max pressure of 100 bar and the other part is feeding the rear levelling system at a max of 200 bar. The actual pressure in the shocks may raise in peaks up to 140 bar, then the releave valve shoud open up.
The reservoir is one and the same for both systems, which explains that all the hydraulic fluid was gone after the failure.
My guess is that the reason for the failure might have been a week spot in the shock tube (manufacturing fault). Knowing the exact dimensions (diameter and wall thickness) of the tube and the material properties (tensile strength), the (ststic) burst pressure could easily be calculated - just to compare it with the 140 bar operating limit. Aluminium is always suspect to fatigue. Unlike steel, it has no fatigue-safe stress limits. Therefore it must be designed with ample safety margin to survive the design live cycle. What is the mileage of the car?

It is interesting to hear the opinion about the Bilstein shocks. The 400i is using Konis with a similar hydraulic levelling system and many of the owners complain about their reliability and are looking for non- Koni replacements.

When I got my 456 GT delivered last October, they had just replaced the rear shocks because of oil leakage ( at 55'000 km's). My 400i is still running with the original Koni's after 50'000 km's and 27 years.

Peter

 

It should read .....the (static) burst pressure....

Sorry,

Peter

 

Wow...

 

I truly dig threads like this one....

 

Tell us more about the other couple? Were they in your back seat? Were they recent participants on "The Biggest Loser"? If you were carrying an additional 300 pounds or so, and the leveling system attempted to raise the aft of the car with additional pressure, and you hit a bump sharp enough that the pressure relief valve could not release pressure rapid enough, then overpressure and failure might occur.

Jim S.

 

Back seat couple was about 325 pounds.

Where is this pressure relief valve ?

 

I assume that there is a bleed hole, similar to the internal workings of a Koni, where hydraulic fluid can cross the piston face. In the absence of such a bleed hole, a rise in pressure in an incompressible fluid may lead to catastrophic failure, as you experienced. The load leveler, as seen on earlier Koni designs (as with the C4, for example) are gas filled, avoiding this potential. As the device has become more sophisticated, and called upon to do more than simply compensate for load, the introduction of fluid was necessitated. There must be a pressure relief mechanism. In the absence of such, an impulse (pot-hole) to the leveler would lead to enormous transient pressure.

I was just pondering whether the increased load in the rear led to maximum compensation pressure, and when combined with a pot-hole, bad things resulted.

I wonder what the specified maximum load (passengers and luggage and fuel) is for the car? Might it have been exceeded, providing an "out" for Ferrari.

Jim S.

 

I understand that the pressure limiting valve is part of the hydraulic level control valve (see attached copies of the workshop manual).
View attachment part1.pdf
View attachment part2.pdf

 

I just yesterday got a copy of the Workshop Manual on CD
(and for $20 post paid, it was my best Ferrari deal yet !)
and saw this language, as you quote.

You would thiink I would get the manual FIRST, wouldn't you.

So, the question now is maybe, is there a presure LIMITING valve
in the shock, or does the presure REGULATING valve (upstream of
the accumulator) do that Job ?

I am thinking that the presure sufficient to give the shock
an Aneurism would blow the flexible feed hose.

Anybody ?

 

OK

Back working on the car after the Daytona
motorcycle races.

BTW, I am a several-times past winner of
the BRUTE HORSEPOWER SHOOTOUT event
at the motorcycle Speedweek. So I attended
this year's event, and saw the "shootout."

Guy #2 makes 569 HP from his Suzuki Hayabusa,
and takes the bike off the Dyno to allow Guy #1
to run his 1994 Kawasaki ZX11 for the title and the
big prize money.

Here's what happens then:

http://www.youtube.com/watch?v=xn3uDC2KC1k

This clip is best on highest def, slow mo, and good audio.

 

I am sort of forming the working theory that the "failure" of the
shock body is because there was high pressure in the shock body
that couldn’t either be bled off, or otherwise
be relieved before the shock “exploded.

This leads me toward the idea that the problem was
caused by something inside the shock body that
was not supposed to be there.

If this object came from “outside” the shock,
how did it get there, and how big could it be?

To get into the shock from the fluid reservoir, the "object" would have to first go through the hard hydraulic lines, through the regulator, and then onto the accumulator.

Here's the accumulator:
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Here's the "port" from the pump and regulator:
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Gaulling caused this. Happens all the time.

"The hydraulic cylinder assembly of claim 5 wherein said sensing means is ..... to galling and scratches in the rod surface which leads to seal failure. ... potentially causing explosive conditions"

 

Using a "drill blank," I find that the hole into the accululator is
about 0.125 inches in diameter.

That means the largest hard object that could enter
the accumulator could measure no more that
about 1/8 inch at the largest diameter.
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Once again neither strange nor rare.

Internal Gauling.

Brought down 737's by gualing induced failure reversing rudder control.

Burst your cylinder.

 

Obviously, the next question becomes:

"If it can get into the accumulator,
can it also get into the shock ?"

Here's the "banjo bolt" that allows fluid into
and out of the shock from
the flexible feed line between
the accumulator and the shock
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The hole in the Banjo Bolt is a
"loose fit" on a 0.208" drill rod.

Therefore, if it can get into the accumulator,
it can get into the shock.
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Probably worth looking into.

The shock body and damper piston moved OK
before and after disassembly.

No debris found in the shock after. That might
be due to the "washing effect of all that oil
going out on the ground, though.

 

That's what happend. In the 737 that went down in Philly it took 56K cycles to duplicate jam and damage to seal was microscopic. Couldn't happen but it did.

 

Thanks for the thinking, Jim.

I am used to the concept you express:
"Couldn't happen but it did."

I am trying to find the physical evidence of
the failure so that, at about $3,500.00 a pop,
I don't have to do this all over again because
I overlooked something.

 

Forget $3,500. Take your car to a race shop and have them re-engineer system with proper cylinders and hydro filters and you won't have this problem again.

I engineered a hydraulic system to lift something a lot heavier than a 456 without issue.

This one is rated at 40,000 lbs capacity.
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