ABC Pulsation Dampener

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?

Peter