Moaning & Groaning
 

I recently acquired a 560sel. It makes noise when the self leveling system is actively pumping oil into the system. As I ride around and the rear end dips down, you hear the oil being pumped. So as the car is bouncing around you hear little moaning sound usually for short bursts. Also when accelerating from a standing start (rear end dips down) you here this noise. The sound is only heard from inside the car. The pump is quiet and if you sit on the trunk and try to make the system pump up the rear end, you cannot hear and sound. It does pump it up however. I suspect that the noise is being transmitted directly to the body through the hydraulic lines or possibly the accumulators or cylinders. I am not sure if the pump is at fault or if this is normal. I suspect it is not normal to hear this noise. When I received the car there was a large leak in the high pressure hose on the SLS pump. I am sure it probably ran dry at some time in its recent history. Maybe the pump is damaged. It does not seem like the pump is bad but maybe it is hurt bad enough that its output has a lot of pressure spikes.

Does anybody know what type of pump this is ? Rotary vane or piston or something else?

Eccentric and mounted on front of engine.

Does the car bounce or float through dips Dave?

Might be time for a set of accumulators if it is bouncing. Blown accumulators could possibly transmit the sound you hear. Remeber, the pump runs full time so the fluid is always circulating through the system.

Mike, I'm glad you replied.

The ride is great it floats thru the worst of bumps. The ride is actually better than my 420's. Accumulators look new. I only hear the noise when the pump is pumping up the accumulators. No noise when the fluid is circulating and the system is stable. Only noise when the valve opens to pump up the accumulators.

One other variable to throw into the equasion.

The hose that I replaced. - I was able to replace the ruber hose portion with a new piece. It turns out that the connectors used are not the crimp type but a type that allows the rubber to be easily replaced. So since the dealer wanted $150 for a new hose - I decided to replace the rubber portion for a grand total of $6. However - the original hose used a fabric type of mesh weave and the replacement is a steel weave. I would assume the steel hose will be "harder" when it comes to absorbing the pump pulses. I suspect that the OEM hose is "softer" and may dampen or absorb the pulses better.

Just a possibe explanation. Do you have any perceptable noise from your car?

My observation may be somewhat biased after years of competitive shooting, but....

I could only hear the flow of fluid when I manually operated the valve lever from under the car. Soon as I would crack the valve in the raise position I could hear the flow of fluid. I have never heard any hydraulic fluid flow while driving.

Be careful with what you use for hose. You're dealing with about 2000 psi.