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Discussion Starter #1
Hi all, had a suspicious "knocking" noise start coming from under the car, maybe in front of the cabin - it only occurs around 800-900rpm and does not appear to vary with engine speed. Occurs whether in gear or in neutral, so not related to drivetrain. I initially thought it was just a bad welding joint on an exhaust heat shield or something. It's very difficult to hear from outside the car. Got under it last week and couldn't pinpoint it anywhere, and with the amount of sound deadening in the cabin, it's extremely difficult and essentially useless to try and pin it down inside.

Then got a loud "grinding" noise on startup yesterday. All of the sudden. Took it to the dealership and a tech sat with me and didn't really address the starting noise but said that the rattle sounds like a bad pulse damper on the steering pump. I guess this is a part I would have formerly called "accumulators" or "nitrogen spheres" on an older, W140 I had with the active self-leveling rear suspension (not ABC).

It's plausible that this is sort of "hydraulic slap" coming from the pump that isn't being taken up by the pulsation damper. I'm going to listen with a stethoscope today.

My question is: does the early W221 arrangement have one sphere, or two? My car DOES have one mounted directly on the pump; the tech thought that meant it was a "revised" system, that has only one. He said prior to this there were two, one inside the front left fender and another one in the front right of the engine bay. I found two parts that claim to match my car - it's a VERY early production model, an '07 assembled sometime in late '06. He thought the revised system didn't get come in until sometime in '08 and was surprised to see that my car had the sphere mounted directly on the PS pump.

Can anyone else speak to this? Have you had challenges with these, specifically on a car with ABC - and doubly so with the M275 V12? Any concept whether there are one or two? Did you do the work or have it done? Did you bleed the system or just top off the reservoir with hydraulic fluid? And... now that I mention it... does this system still use CHF11S?

Thanks!
 

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I own S550 with ABC (the same as in in S600) - there are three accumulators - one on tandem pump (pulsation dumper - can generate noise/knocking/shacking on low engine speeds), second in on front block valve (under left front headlight - accessible from bottom of engine cover), third for rear block valve is located in trunk - left side of spare wheel).
 

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Discussion Starter #3
Thank you - I replaced the pulsation damper on the PS pump (p/n 0004660310) and the rattle / knocking noise at low engine speed has gone away. There was also an intermittent creaking noise in the power steering especially when the engine is cold and the car is not in motion, or moving very slowly, which appears to have gone away. I had attributed that to worn ball joints but it appears this can be a symptom of a failed pulsation damper as well.

I also bought an accumulator - which is much larger, and I'm assuming is the one inside the left front fender or in the trunk. However, given that the noise has entirely vanished (as well as a prominent "whining" noise when accelerating) I'm assuming that the pulsation damper was the failed part. The hydraulic fluid level was also a little low - but the volume required to re-fill the system was very precisely equivalent to the volume of the pulsation damper. If one of the larger accumulators had failed, I suspect the reservoir would be VERY low, nearly empty. I'll just put the accumulator on the shelf.

Thanks!
 

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Hey I also have a 2007 Mercedes S600 with the same issues you had on your S600. I'm trying to repair it myself, is the damper easy to take off? And when I take it off will there be any oil leaking? What tools do I need to take it off? Thank you.
 

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Hey I also have a 2007 Mercedes S600 with the same issues you had on your S600. I'm trying to repair it myself, is the damper easy to take off? And when I take it off will there be any oil leaking? What tools do I need to take it off? Thank you.
I replaced mine on my 2008. Easy to do on the V12. Would be easy while your doing the coilpack. Clear the area from the top I think there is a hose you need to move to the side plus the intake tube and maybe the filter housing. From there you will see the part it simply unscrews. IIRC there is a hex head built into the top of the damper to get a socket on (I think). I cleaned the area with compressed air prior to removal. No fluid came out for me. I noticed a whine that was RPM related and traced it to the damper and problem solved when replaced. Only ABC issue I've had in 115K miles.
 

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Hello, i already changed the damper, but the noise continues, i thought changing the damper would resolve the issue, do i change the power steering pump? there is whine noise when i steer left or right, i will change the coil pack later after fixing the whine noise issue. Thank you so much for your help.
 

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I replaced mine on my 2008. Easy to do on the V12. Would be easy while your doing the coilpack. Clear the area from the top I think there is a hose you need to move to the side plus the intake tube and maybe the filter housing. From there you will see the part it simply unscrews. IIRC there is a hex head built into the top of the damper to get a socket on (I think). I cleaned the area with compressed air prior to removal. No fluid came out for me. I noticed a whine that was RPM related and traced it to the damper and problem solved when replaced. Only ABC issue I've had in 115K miles.

Hello, i already changed the damper, but the noise continues, i thought changing the damper would resolve the issue, do i change the power steering pump? there is whine noise when i steer left or right, i will change the coil pack later after fixing the whine noise issue. Thank you so much for your help.
 

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2008 S63. Going to change out my pulsating damper soon as it arrives. Wondering if anyone has experienced whine from power steering when turning at low speeds? Also had fluid coming out of actual power steering reservoir with bubbles. Could this all be symptoms of a bad PD or something else? Could the bubbles be from the nitrogen escaping the system? Ride doesn't seem rough and I don't have any ABC messages on dash. Filled up the fluid to level and still have the whining noise.
 
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