Thread: Bouncy 560SEL
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Old 11-18-2000, 09:36 AM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Definitely ACCUMULATORS. Possibly aggravated by beat upper strut mounts.

On any hydraulic suspension systems accumulators are the actual springs. They are steel spheres about 4-5in. in diameter. Inside is a diaphragm with high pressure Nitrogen gas (say 1000psi - it varies in different systems and I don't remember the exact spec for this case)holding the diaphragm against the wall.

As system pressure builds, at 1000psi the fluid starts compressing the gas and the diaphragm leaves the wall. At say 2000psi the fluid now has compressed the Nitrogen to half the container with the hydraulic fluid pressing on the diaphragm in the middle of the sphere and the car is now being lifted.

If at this moment a bump is hit and the suspension compressed, the strut squeezes the fluid into the accumulator against the gas pressure and the pressure raises to say 3000psi. Now the pressure rebounds and expands the strut in recoil. This action is in effect a gas spring taking advantage of the compressibility of a gas.

Once the gas is gone, the whole system is a non-compressible fluid AND it is non-compressible. Driving in this state tears the poop out of every thing.

If you can visualize the conditions that I portrayed with a fully charged chamber and then one totally dead, then you need to visualize the states in between. As the system looses its gas differing amounts of strut movement cause bottoming out.

I recommend replacing these chambers at mile intervals because their relative state can't be determined except with either great experience or expensive testing. We have done our shop wagons at 60-90k intervals.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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