Nitrogen is probably soluble in the fluid at high pressure. As is gets recycled through the system it's solubility will drop on the low pressure side thus losing the nitrogen to the atmosphere. Pretty soon, no nitrogen left.

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For Sale: 1982 MB 300TD
1995 Chevrolet Suburban 6.5TD

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel

Since the gas compresses it "mixes" with the hydraulic fluid and creates a foam with each bounce. The foam recirculates into the reservoir and the gas is released.

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Chad
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys

I scored a good pr at the local scrappers.

I think they charged me like $4/ea.

yeah for me..........

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1984 123.193 372,xxx miles, room for Seven.

1999 Dodge Durango Cummins 4BTAA 47RE 5k lb 4x4 getting 25+mpgs, room for Seven.

The diaphragm is round and contained inside the frame of the ring?

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1974 240D 3.0L 4(M) - 250K -OM617.910 + 300D FW + Rajay turbo power!
1977 6.9 3(A) - 84k

I'm having trouble wrapping my brain around how the system works...

The accumulator absorbs shock, correct? What controls dampening? It seems like there must be a valve, or something that slows the fluid down as it moves with the suspension to dampen the movement, much like a conventional shock would. If there wasn't, and there were only nitrogen spheres, wouldn't the sphere just act as a "spring" and the car would just constantly bounce over bumps?

I've seen the SLS fail in two different modes...one is excessive bouncing at all times. (When the rear of the car is bounced manually, it keeps bouncing 6-7 times after you stop). The other failure mode is an ultra harsh ride...you can feel every bump, and imperfections in the road slam you into your seat, and/or make your head hit the roof! Can anyone explain why this happens?

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

On the w123, the SLS works as a system. The dampening comes from the accumulators and coil springs working together with the SLS valve. The valve body has 3 valves inside: fill valve, release valve and a base pressure valve.

The actuators only control ride height based on the adjustment of the SLS valve linkage.

If you have an extra bouncy or hard ride*, you need to replace the accumulators.

*I believe this is also an indicator of the condition of your coil springs. If you have an extra bouncy ride with shot accumulators, the springs are doing their job. If you have a hard, jarring ride, the coil springs are worn.

On other SLS systems where they aren't self bleeding like the w123 and w124, I think the extra hard ride can be due to the fact that hydraulic fluid doesn't compress. When the bladders fail, the gas aerates/foams into the fluid, there is no more dampening/cushion and the ride becomes hard.

This is the way I understand the system after rebuilding the one on my wagon.

__________________
Chad
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys

The nitrogen it under high pressure. If you look at the original picture I posted, you'll see the sticker that say "WARNING, High Pressure". Yeah the one that I cut right through!

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Ah, I didn't notice that in the picture. Hope you didn't get a big PFFFT in your eye
That makes sense then, the pressure would be much lower and offer less compressive resistance. And then the foaming action that Chad described is probably a good explanation as to where the rest of the gas goes.

I've asked this before. I think there are small orifices in the cylinders that the hydraulic oil must pass through (like a traditional shock absorber), and that provides the dampening. As the cylinders compress, forcing the oil through the orifices, the oil moves through the piping to the accumulators, where it compresses the nitrogen, which then springs it back through the system to the cylinders, and has to pass through the orifices, taking energy from the initial input force. Holy run-on sentence.

Anyway, there has to be something that restricts the flow of the oil, the cylinders make the most sense to me, but it could just as well be in the leveling valve. Just my thoughts, could be completely wrong.

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

I noticed while removing the accumulators from a junkyard car, that when I cracked the line nut, a lot of foam came rushing out, and smelled kinda funky. It foamed for quite a long time, then there was just a constant flow of fluid. I'm assuming this was nitrogen gas?

So it almost seems like, depending on the circumstances, the nitrogen gas sometimes gets trapped in the sphere, even though the diaphragm is bad?

Either that, or it just takes a LONG time for all of the released nitrogen to bleed from the system, while normally operating otherwise. This almost makes sense to me, and seems like it would cause the "bouncyness" failure mode. If there are bubbles of nitrogen in the pressure lines, the rebound can't be dampened...but it would still provide some shock absorption, since the gas is still being compressed in the lines.

Am I in the right *line* of reasoning?

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

Can anyone recommend a DIY link to replacing accumulators for the W123 and W124. I am currently trying to replace a pair on my W124 and am having difficulty. not sure about fluid leaking concerns, should I plug something? how much will I lose? (how much replacement fluid should I have on hand), how do I get at the accumulators on the W124. I am removing the interior and still cant see them. The carpeted panel between the 2nd and third row doesnt budge and I think that is where they are. I have removed screws, and it (panel) is still rock solid.

thanks in advance.

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.

It took less than 3 qts for me to refill. That carpeted panel is where they are, I think there are 4 screws.

The panel is thin sheet metal, will yeild a bit but after the four screws (two in the 3rd-seat opening, two on the horizontal surface hiding in the carpet) are removed the anti-rattle foam strips will act like 2-sided tape, takes a little work.

They are pretty straight-forward to replace. I found that installing the new ones was a bit tricky, get the small hydraulic lines' threads started before bolting the accumulators down, the passenger-side one is a ***** to line up as it is very short and difficult to move into position.

As far as fluid, I bought 2liters, which was enough but a 3rd liter was necessary to properly purge. I drained the reservoir, poured a liter of fresh fluid in, stuck the return line into the empty container, continued pouring fresh in until the return fluid was clear.

After you run the car a few times, the dirty fluid from the dampers will mix with the new, and a 2nd purge is not a bad idea if it was really nasty (or unknown).

Oh, and you'll need 4 new crush washers for the banjo bolts.

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Gone to the dark side

- Jeff

Here's my change on a w123

Jeff,

Any chance you have the part number of the crush washers handy?

Chris

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1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

.. suppose for a moment a guy with an SEC with Rear SLS only and new accumulators with all working well.

Then one day he got bored and had a spare set of new accumulators, made a T-fitting and plumbed in the spare accumulators so now each side had 2 good spheres instead of 1 for a total of 4 in just the rear.

I wonder what the change would be. Is the load now spread among the 4 spheres and is more dampened which might be nice with the firmer H&R springs?

Just thinking out loud.
Great pics.

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*****
Thomas Johnson
Phoenix, AZ USA
1988 560SEC