The Mysterious Insides of an Accumulator Exposed! - PeachParts Mercedes-Benz Forum

pcmaher · #1 08-23-2004, 08:52 AM

Well, as some of you may know, I replaced the accumulators on my 95 S600. With the help of my fellow Forumers, I now understand exactly how the suspension works in this car. Thanks again to everyone who helped out. I thought it would be interesting to take a peek into one of my old accumulators. So, I cut one of the old ones open, and took some pictures for us all. I first drilled a small hole in the round end, just in case there was any gas charge left in there (safety glasses naturally). I doubted there was, but you never know. There was no gas at all. I held the accumulator in a table vise, and started at it with a hack saw. It took quite a while to cut the end off. It's made of a relatively soft steel, and the wall is about 1/8 inch thick. By the time I was done though, the hack saw and housing were smoking from the heat. After looking around the inside of the thing, I see how it's supposed to work. It's not a simple flat piece of rubber dividing the sphere...it's more like half a rubber ball inside the steel housing. The damage you see was caused by me sawing the thing in half. I thought that the rubber was more like a flat diaphram located at about the halfway point in the sphere. Picture a football with half of a contoured rubber bladder inside. The leather functions like the steel part, and the bladder functions as the rubber part does. I didn't see any holes or tears in the rubber. I'm guessing that the plastic piece you see in the center of the rubber is a check valve used to charge the sphere with nitrogen. Perhaps that slowly leaks over time. The check valve in my new accumulators was just visible in the larger of the two openings in the steel part. There was fluid on the wrong side of the bladder.

Harold in NC · #2 08-23-2004, 06:57 PM

Pretty cool.

Inthemedia · #3 08-24-2004, 11:55 AM

So what do you think failed in them. There doesn't seem to be a whole lot inside of them to go wrong. I always thought that accumulator failure was due to a ruptured diaphragm but this doesn't seem to be the case at all. Due you think there is any way to renew them without having to take them apart?

pcmaher · #4 08-24-2004, 05:06 PM

It's hard to tell, I didn't really look at the condition of the rubber too closely. Perhaps the rubber deteriorates and becomes slightly porous, allowing gas to leak out. Or, the check valve slowly leaks over time.

Kebowers · #5 08-24-2004, 08:46 PM

The nitrogen slowly diffuses through the rubber diaphghram and into the oil on the other side. This is the usual 'failure' mode. Sometimes the rubber cracks and the oil and nitrogen mix quickly--though this is unusual.

I can recharge themif its worth it. What do new ones cost?

pcmaher · #6 08-25-2004, 08:11 AM

I got them for $97 each from Phil. Is that plastic piece embedded in the rubber the check / fill valve?

BenzRepair · #7 08-25-2004, 11:35 PM

Quote:

Originally Posted by pcmaher

I got them for $97 each from Phil. Is that plastic piece embedded in the rubber the check / fill valve?

I believe that plastic piece you refer to is there to protect the rubber bladder from damage due to violent motion of fluid entering and leaving the accumulator via the fluid entrance hole.

#8 10-17-2004, 06:46 AM

Hi,

I saw these photos with great interest as you can imagine. I put second hand spheres in my 250TD and they are just as bad as the originals.

From what you saw in there, do you reckon you could poke a tent peg into the hole of a sphere and tell if there was gas in there or not? I did this with the shot ones I removed and you could tell there was no gas in ther because the diaphragm was flat against the curved end of the body.

I only ask because I can get another 2nd hand pair on warranty from the wrecker, but I don't really want to put in another pair of duds!

I have had a great run with 2nd hand parts in general because the Merc parts are so well made, most are in fully functional condition off a car with 200K on it, but spheres are probably the exception to the rule.

I feel, though, since I've got the chance at some free ones and the connections are already loose and smooth, I figure if I poke a pencil in the big hole I should be able to feel the diaphragm about halfway down the sphere?

Thanks for input.

JamesK

pcmaher · #9 10-17-2004, 04:07 PM

My guess is that you could check for pressure that way. But be very careful about not using anything sharp. You obviously don't want to poke any holes in the rubber or damage the check valve. My concern would be a sphere that has some pressure in it, but not enough to function properly.

stevebfl · #10 10-17-2004, 05:12 PM

I'd sooner use used motor oil than a used accumulator. They are disposable and perishable. They should be replaced every 100k whether they have symptoms or not. By the time the symptems are noticable the system has been thoroughly stressed.

They can be tested fairly easily once on the car if one has the gauge to hook to them. Only thing is if I were testing them I would probably charge more than the price quoted in this thread for new ones. Kinda silly.