I changed out the accumulators on my wagon today. The rearend bounced like crazy going over small bumps. It would almost make a person seasick in the back seat.
I thought I would cut one open to see what was inside for my own interest and all the forum folks as well. There is a ring inside that holds a rubber diaphragm. On one side of the diaphragm is suspension fluid and the other is pressurized gas(not sure what kind of gas). When the diaphragm ruptures it fills the whole accumulator with fluid causing the rearend to bounce.

Rubber diaphragm down:

Rubber diaphragm up:

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Cool. Gas is nitrogen I think.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

What did you cut that open with? Thanks for the view inside. I've replaced 4, and at least now I can visualize the guts....

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

My sharp whits!

I used an angle grinder. It's really thick steel I was quite surprised.

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Wow, so there's no way to test these spheres off of the car?

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

Fill it with oil and measure the volume it takes vs the volume the body displaces. If the diaphragm is intact the volume of oil will be relatively small.

Cool, I did the same thing with the engine mounts when I replaced them...

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Yes- take a rod with a blunt end and attempt to push the rod into the sphere. If it pushes down easily the sphere is no good. If it's difficult or you cannot the sphere is good. The volume of oil means nothing- a bad sphere may displace a small amount of oil but show little resistance and be worthless. You'd have to wait for some time for the oil to seep. Pushing a blunt rod takes only seconds anyways. A phillips screwdriver will work in a pinch- just be sure to push in the center.

With a little bit of adaptation, you could replace these with Citroen spheres. The later ones use the same hydraulic fluid as the accumulators and they last 20 years. I've got some early ones that have lasted longer. And the older ones are rebuildable with parts still around. They come apart and can be re-gassed and reused for about 20 bucks.

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Strelnik
Invest in America: Buy a Congressman!

1950 170SD
1951 Citroen 11BN
1953 Citroen 11BNF limo
1953 220a project
1959 180D
1960 190D
1960 Borgward Isabella TS 2dr
1983 240D daily driver
1983 380SL
1990 350SDL daily driver alt
3 x Citroen DS21M, down from 5
3 x Citroen 2CV, down from 6

I have several spares in my garage- no need to change nuttin...

If you have a dead one, can you send it to me so I can so some experiements? I re-gas the Cit ones and have built a set-up to do it.

I can probably regas the accumulators as well, although they look like some of the newer ones that are not made to be regassed.

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Strelnik
Invest in America: Buy a Congressman!

1950 170SD
1951 Citroen 11BN
1953 Citroen 11BNF limo
1953 220a project
1959 180D
1960 190D
1960 Borgward Isabella TS 2dr
1983 240D daily driver
1983 380SL
1990 350SDL daily driver alt
3 x Citroen DS21M, down from 5
3 x Citroen 2CV, down from 6

I think the failure mode for these items is the diaphragm, which lets the nitrogen leak out. You can't disassemble the sphere (as with a Citroen sphere) and replace it - it's a welded unit. Adapting Citroen spheres might be interesting, as it would provide you with rebuildable parts in the suspension. But you still have the expensive struts to worry about...

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1984 300TD

I don't have any dead ones- I test them in the yard so i don't waste $ buying a bad one.

Have you ever found any good ones in the junkyard? I've only been able to find blown ones.

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

I wonder how the gas gets out. Isn't this mounted upright under the car? Even if it was sideways, you'd think some of the gas above the hole would remain in there...maybe its pressurized and when the diaphragm tears the pressure drops to near atmospheric and there's not enough "spring" left.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now