Very strange .......

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.

 

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).
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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"

 

Once again neither strange nor rare.

Internal Gauling.

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

Burst your cylinder.

 

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.

 

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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