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ABC Pulsation Dampener

32979 Views 22 Replies 13 Participants Last post by  JettaRed
My 2003 SL55 has 151,000km now, 70,000 of those are mine.

There has been a bit of a drone with the engine running for some time now. It varies with engine revs and is only really noticeable with the roof up.

The ABC pump died a few years ago at about 120,000km and I replaced the suspension accumulators a year or so ago.

After reading a few posts it seemed as if the pulsation damper, which sits in the left front wheel arch in my car, might have been the culprit. It was probably the original and if its diaphragm was going to be anything like the suspension units it was due to be replaced anyway. Later model cars have the damper attached directly to the tandem pump

I bought a new unit on ebay, some sellers don't ship to Australia; mine arrived in about 10 days and it came in a genuine MB box. The part number is A 220 327 02 15 from parts4export and it cost $US170 + $49 postage

It's an easy job to do and there are various posts about how to go about it. The hardest part is removing the inner plastic wheelarch. You need a fairly thin 24mm open ender to undo the damper and a 22mm open ender to hold the valve. It's a two minute job once you have got that far. I had a bit of a problem starting the thread on the new damper, it needed a bit of a push in while screwing it on. There's no need to do any fancy bleeding, I probably lost a few mls of fluid when I undid it which was easily caught in some cloths. When I started the car there were no red or white warnings and the drone seems to have lessened.

I dismantled the damper to find out why it failed.

The upper part of the damper is pressurised so be VERY careful if you try to do this at home. I drilled a small hole in the centre of the dome with the dampener held in the mill vice and a plywood shield between me and the job.

The first indication of why the unit had failed was there there was no hiss as the drill broke through.. When I turned the unit upside down oil ran out.

Inside these units is a rubber diaphragm and on the side I drilled there should have been a heap of nitrogen and no oil.

I parted the damper off in the lathe to remove the diaphragm and the pictures tell an obvious story.

The diaphragm is severely cracked in numerous places and, although there are no obvious perforations, it has delaminated and allowed oil through into the pressure side.

It wasn't doing any damping of anything

I can't find anything about when these pressure devices should be replaced.

They will not last forever and they will fail affecting the performance of the car

So when should you replace them?

My car, at 12 years old and 150,000km went too long. 100,000km was probably too early, maybe 120,000km would have been about right

In hindsight I should have replaced it when I did the accumulators

I know that there is another return line damper buried somewhere near the transmission tunnel but I haven't heard any reports of symptoms if it fails (it has probably already failed)

Any serious reason for doing it as a precaution?



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Great post Peter! Glad to see you were curious and wanted to look inside. This is the first I've seen of the inside.

From my understanding this dampener takes the most load, as it sees pressure spikes directly from the pump. When this unit fails the pressure spikes get sent to the rest of the hoses, valves, and shocks downstream. So there is a cascade affect. Best to just replace it.
Mine had already failed at 12 years and 85K miles (136K kilometers) when I replaced it. I agree that 10 years and 75K miles it is due for replacement.

The return line dampener you mention takes the least load, as it is furthest from the pump, and dampens the return fluid from the valves to the reservoir. I've never heard of this one failing on the R230, and if it did would likely not cause any issues or harm. Mine is still original.

One last data point...I replaced my 2 valve block accumulators at the 12 year/85K mark and they were both still good. Probably not for long though.

This is a preventive maintenance item that all R230 owners should take part in. For around $600 DIY you can keep this system healthy for another 10 years.
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Very nicely done and appropriate Cowiepeters. I'm sure many will find it helpful, and perhaps a 'stimulus' to replace theirs BEFORE the bladder ruptures.

I replaced both dampeners and accumulators at 12 years and 50K miles last winter. None of them had failed, but this seemed to me to be good 'preventive maintenance insurance' for the rest of the system. Doing labor myself, it cost about $5-600 as I recall for all four items. Several hours of labor. The left rear is a 'bi***' to get out for replacement, but there are good procedures on this and other forums. Glad it's done - shouldn't need it again for another 12 years and 50K or more miles.
Many, many thanks for that most informative post, Cowie. I wish you were my next door neighbor ... I think my R230 needs a similar do-over. I appreciate your taking the time to post your information and especially your pix. Great work, Mate!
Pulsation Damper

I would like to thank everyone for the posts here as well. I first found the exact sound my 2008 SL 600 was making on youtube (
) . I then came to our site and found these posts.
I just had mine replaced and it cost $450.00 for part and $200.0 for labor (Canada). I would like to clarify that it is called a "Pulsation Damper" not dampener. The site saved me hours of troubleshooting. Thanks again.
I can't get the pulsation damper off the valve body. I've soaked it with pb blaster. Where did you use the 22mm wrench to hold the valve body? Did you remove the valve body from the wheel well or remove the damper while the valve body was still connected to the 3 hoses? Thanx
You need a thin wrench to remove the Damper from the valve body. You must counter hold the valve block while breaking loose the Damper. I just did mine a couple of months ago and don't remember the Damper being that tight on the valve.

I did all the work right inside the wheel well without removing any lines. Just have to unbolt the valve block and move it out for access.

See attached instructions



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As Bob says you will need two open ended spanners to remove the damper, you will never get it off with just a spanner on the damper.

I ended up "thinning" a spanner so that it would go on the damper and held the valve body with the other spanner

It was tight but not stupidly tight

Manipulate the two spanners so that they are almost in the same long axis, the top one should be just "behind" the bottom one. like a bit clockwise.

Squeeze them together and you will get a satisfying crack as it releases

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Confirming Peter's procedure. I had a thin 22 mm wrench in my tool box, so was lucky.

Also, for Aussie, Kiwi, or other owners looking for parts, I have a friend in Texas who started his business selling parts for Porsche 928's, but later expanded into BMW, MB, and other models of Porsche. He ships all over the world (moved to US from England about 20 years ago). He can source OE MB or after market parts, and his prices are attractive vs dealers. Here is his e-mail address if you want to pursue sourcing from him as an option (you may need the MB part number): [email protected]

His name is Roger Tyson, and you can reference me as a source of your information.

I'm planning on replacing my front dampener and accumulator this weekend. I would like to double-check the slim wrench sizes needed before ordering some.

I see both 20mm and 22mm mentioned in the thread. I don't see 22mm listed on many, if any, wrench sets. Can I ask for clarification on the size of the slim wrench needed on the dampener?
24mm for the pulsation dampner, finally got it off and the abc system is still making the clicking sound at low rpm,
good luck w/ yours
why would one of the hoses from the valve body assembly that has the pulsation dampner be warm but the other hose is not warm?
maybe a blockage?
If all 4 corners are rising and lowering when you press the ride height button, then I doubt it is blockage related. I would expect the line coming from the pump to be hotter. My guess is the mass of the pulsation dampener may be helping to radiate the heat before it enters the other hoses.
actually, just occurred to me that one of the lines coming from the assembly is the return line for the pressure overflow valve. It diverts fluid to the reservoir if pressure exceeds 200 bars. So that line is mostly idle and as a result would be cooler.
I had the two rear accumulators replaced about 18 months ago when I started getting drive carefully messages and the reservoir started overflowing. Today I replaced the front accumulator and pulsation dampener. I wasn't having any symptoms. I just wanted to be sure I was running on 4 fresh accumulators.

I was surprised to discover the front main accumulator was blown, even though I was not having any symptoms.

So I guess the lesson is that if you start getting "drive carefully" messages, then both your accumulators are probably blown. Replacing one will get things working again, but odds are the other main one is blown as well.
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Replaced my pulsation damper on 2003 sl500 85k miles recently
Firmed up the suspension. As mentioned removing inner liner was the most difficult part of the job.
Will rebuild valve blocks and accumulators around 100k miles
Pulsation damper is always mentioned as the first part to wear out. Mine began humming 6 months ago. Finally replaced it before a 2000
Mile February trip, to the sunshine state. 821 miles 12 hours 15 minutes door to door. Interstate 95 "racetrack"
Spring is around the corner
Looking forward to my "other car"
The convertible

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Hi guys

Do I have to release the system pressure before removing the pressure damper?
Do I understand correctly you just remove the old an install the new damper, top up fluid and toggle ride height a few times and that's it?

Hi guys

Do I have to release the system pressure before removing the pressure damper


See my post 7 in this thread for instructions which says "engine must be switched off for at least 5 minutes". System bleeds pressure off fast.

Do I understand correctly you just remove the old an install the new damper, top up fluid and toggle ride height a few times and that's it?

Good luck,

Thanks for the help Bob, it was just as easy as you said, job done in less than 30 minutes.
It took me a minute to realise I must put the 22mm on the valve body, I was looking for a 22m nut.

I replaced the right front strut with an Arnott unit a few days ago and now the pulse dampener, I have to agree with others that worked on the ABC system it seem to really be an easy DIY. - That is naturally with all the help available on these forums!

Hope I can be of some assistance to someone in future too.
Hi Guys,
I'm getting that nasty hum, I'm hoping its the pulsation damper.
I have a 2007 SL550. From some of the previous threads I've read it said the pulsation damper was on the actual ABC pump. This thread shows it behind the wheel well. Is there more than one pulsation damper?
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