How do you check nitrogen spheres to see if they have failed?

[samiam44]

Good morning forum!


I don't know for sure, but I think my 500e is a little harsher than I remember? I do run 18X10 tires @ 32 psi. I was looking through the suspension section on the FSM and did not see testing of the spheres or R&R procedure. Via our list, I did see a mention that they are mounted in the spare tire well.


Michael

 

[nocfn]

Typically, you bounce like you are on only springs.

If you remove the sphere and fitting, insert a #2 pencil into it with eraser end.. If it goes in farther than half way-the bladder holding the gas is weak or leaking for soon failure. YRMV


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[nocfn]

Also if Luckymike is reading, maybe he will post pics of a write up he did when he did the job. It is a chicken/egg type of issue since the struts raise level and provide some cushion, it is the springs that hold it up and the spheres that dampen. Spheres weak can lead to strut issues and vice/versa.


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[gerryvz]

There is a HOW-TO already posted, in good detail, on the sphere R&R procedure. No sense to re-invent the wheel with another redundant HOW-TO.

To test the spheres, I have already posted how to do this. It is quite simple:

1. Go to the rear corner of your car
2. Place both hands or 1 foot on the corner of the bumper
3. Press down as quickly and as hard as you can
4. If you get one good, long downward damping motion, and a quick smooth rebound, and a second very slight downward bounce and smooth slight rebound to normal position, the sphere on that side is "good"
5. If you get a rubbery motion and little to no actual smooth damping motion, the sphere on that side is bad
6. If the rear of the vehicle feels "bouncy" and rattles your teeth when going over speed bumps or other road irregularities, then the sphere(s) are bad
7. If the level of hydraulic fluid in your SLS tank in the engine compartment rather suddenly decreases significantly, then your spheres are very likely bad

Hope this helps.
Cheers,
Gerry

 

[gerryvz]

Here is the HOW-TO for replacing the rear suspension accumulators.

EDIT: Link updated:

HOW-TO: Replacing W124 Rear SLS (Self-Leveling Suspension) Spheres | "HOW-TO" Tutorial Articles

Starting around the May 2022 time frame (and possibly before), I noticed on several long-distance trips up to the NYC area, that the damping and bump-absorption capability of my E500's rear suspension was severely diminished. It was basically not absorbing bumps, and every time I would drive...

www.500eboard.co

It is for the V/C126 chassis, so the spheres are mounted UNDERNEATH the car rather than in the trunk as they are with the .036, but fundamentally the procedure is the same because the systems are near-identical (even utilising the same level-control valve and SLS tank and filter and fluid).

Cheers,
Gerry

 

[gerryvz]

the struts raise level and provide some cushion, it is the springs that hold it up and the spheres that dampen. Spheres weak can lead to strut issues and vice/versa.

The hydraulic rams in the rear are NOT shock absorbers. Rather, their primary job is as hydraulic system stabilizers and cylinders whose main function is to provide hydraulic fluid to the accumulators (spheres) under high pressure. They are also the mechanism that retains the set ride height based on the adjusted position of the leveling arm and valve, with the load-leveling depending on how much weight is being carried in the rear of the vehicle.

The accumulators are what handle (dampen) the up and down motion of the suspension, with the steel coil springs assisting where needed.

Cheers,
Gerry

P.S. I've attached a PDF document about the hydropneumatic system that was authored many years ago by my friend Neil Dubey, who owns Star Motors in Endicott, NY. It's geared toward the 450SEL 6.9 and V126 models with "full" four-wheel hydropneumatic suspension, but it applies well for the .036, wagons and other models with rear-only hydro suspension.

 

[nocfn]

Yea, what honch said!! [emoji595][emoji595]


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[Glen]

Sorry Gerry, I don't agree with you on this. Maybe it's semantics, but the damping of spring and suspension movement is absolutely controlled by what you call "hydraulic rams" or also known as hydrostruts. The nitrogen spheres act as reservoirs for fluid displaced by the hydrostruts and also as "springs" to help support the car but because they do not contain valving to restrict/control fluid motion they provide no motion damping. Again, perhaps it's semantics.

 

[gsxr]

Normal gas-pressurized shock absorbers are self-contained, all in one tidy unit. The MB SLS system turns this into a 2-part setup where the gas pressure is separated from the mechanical portion. (OK, fine, 3 parts with the external hydraulic lines... 4, 5, 6 with the valve.. pump... hoses... etc).

Semantics, yes: Although the SLS hydroleg itself is technically not a shock absorber, the overall system functions as a shock absorber. A fancy one that does more than just absorb shocks.

 

[Klink]

Miss you guys. I've been too busy to rant on for a while, and it's bugging me.

In practical applications as far as what needs to be repaired, this is nitpicking, but there are some misconceptions about these systems, in particular there seems to be a perception that the SLS and full hydropneumatic struts are little more than hydraulic rams, with oil "on top" of the piston forcing the piston out. This concept is inadequate. There is also a frequent confusion of the concept of "damping" with the concept of "springing".

All of the SLS struts, and full hydropneumatic struts too, for that matter, ALSO function fully and completely as conventional shock absorbers. Absolutely, completely, 100%. The plate valves in those struts ARE the dampers. They have a plate valve stack on top of the piston exactly as in a conventional Bilstein type shock, and the "damping", that is to say, motion resistance, bump energy dissipation, and resonance tuning are managed at the plate valves just as in a conventional MB type shock. The piston rod is 100% surrounded by oil from top to bottom, and the plate valve stack is always moving "through" the oil with any movement of the assembly.

For damping resistance, the plate valves get jammed together more tightly during more rapid movements, and have less resistance against them during slow movements, creating a nonlinear rising damping resistance relative to motion. That's a cool old school MB/Bilstein design.

The oil displaced by the volume of the strut rod additionally compresses the gas in the sphere, and this creates the additional helper SPRING force for SLS functionality.

SPRING FORCE comes from the sphere. DAMPING RESISTANCE comes from the friction of the oil going through the plate valves in the strut.

In fact, it is vastly more accurate to think of these as conventional shock absorbers simply having larger diameter piston rods and a very large external gas pressure chamber with a variable externally controlled oil volume!

They aren't simple hydraulic rams, and the concepts of springing and damping need to be kept separate, because they are. The spheres aren't "dampers", they are air springs. They do virtually no "damping". The "dampers" ARE inside the struts.

More to come, gotta run.

Like I said, miss you guys, and we really wish we could've been at the GTG...

 

[nocfn]

Yikes a mushroom cloud over the discussion. Man I have copy and pasted this, for when I am asked, and can now be better then generally right, rather than absolutely wrong. Thanks Klink and for the record of personal experience, I'm new installs on my c126 in back all around, and new spheres on the E500. Both work great, great systems and I would never delete them.[emoji85][emoji90]


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[gerryvz]

Normal gas-pressurized shock absorbers are self-contained, all in one tidy unit. The MB SLS system turns this into a 2-part setup where the gas pressure is separated from the mechanical portion. (OK, fine, 3 parts with the external hydraulic lines... 4, 5, 6 with the valve.. pump... hoses... etc).

Semantics, yes: Although the SLS hydroleg itself is technically not a shock absorber, the overall system functions as a shock absorber. A fancy one that does more than just absorb shocks.

You summarized what I was trying to say very succinctly. I think there's also some confusion over the word "dampen" here.

A lot of people confuse the hydro-leg as being the same as a self-contained gas strut, which it is NOT. I have had numerous discussions over many years about SLS/hydro suspension system with experts, and my understanding has always been that it is the spheres that do most of the shock damping, with the rubber membranes inside (with oil on one side and nitrogen on the other) providing the "spring" capability that softens the ride. Of course the hydro-leg has a tube and provides up and down motion control, but it works together with the sphere and the compression of the nitrogen inside the sphere is what provides the cushioning effect when the car hits bumps.

My use of the term "hydraulic system stabilizer and cylinder" with relation to the hydro-leg was intended to characterize the hydro-legs as up-and-down control points that provide suspension stability, and also a pressurized container (reservoir) for the hydraulic fluid that is located close to/directly plumbed to the spheres (accumulators) to keep a constant hydraulic pressure for both shock absorption, and level control.

No worries, I'm very familiar with the system and have worked it starting 15 years ago when I had my 450SEL 6.9 (which has five accumulators & four hydrolegs comprising the system), so I don't need to comment further on the topic.

Cheers,
Gerry

 

[Randy Crooks]

I had a bad sphere on my car and cut it apart today to see how the rubber bladder is made and where it's positioned in the canister. There is a fine line around the canister and that's where I cut it,the rubber is crimped in place just about 3/4" below that parting line.

There are two pictures here of the shock absorber piston and the disc valves that mount on top and bottom the piston.

Randy

 

[Jimbo]

My 2 cents as a long time owner on original rear struts....always replace the N2 cells first...as they are cheap (as compared to the struts themselves) and usually the fail item in the SLS system on the .036s.

That's not to say the hydro-struts don't fail, they can and have, but generally they are long lived. Very recently, about $60 for the N2 cells each and $450 for the hydro-struts each, wholesale. For a friend's car btw...he said he wanted to do both and had the cash burning a hole in his pocket

 

[Jim]

I know this has been discussed ad nauseam but these pictures really bring clarity...thanks Randy.

We see hydraulic fluid can pass through the piston and the stiffness tuned by the design of the washer stacks above and below.

The only part of the system that is not crystal clear to me now is if the inlet/outlet of the sphere has any throttling effect. I think someone suggested that the diaphragm can be pushed with a pencil through the sphere inlet/outlet port...therefore that is larger than the connecting pipework bore and so...to answer my own question...no, there is no throttling effect.

Jim

 

[DarkStar]

I noticed my left rear seemed a bit hard the other day. I tried the bounce test. I pushed it down, it came up and then down slightly, then up to a stop. All good based on that. Maybe the hydro-strut is failing? I flushed the system last spring. Seemed good, but lately I have also questioned whether the leveling valve was working properly.

 

[MY911S]

Here is the HOW-TO for replacing the rear suspension accumulators.

http://www.500eboard.com/forums/showthread.php?t=3050

It is for the V/C126 chassis, so the spheres are mounted UNDERNEATH the car rather than in the trunk as they are with the .036, but fundamentally the procedure is the same because the systems are near-identical (even utilising the same level-control valve and SLS tank and filter and fluid).

Cheers,
Gerry

@gsxr the hyper link to the procedure looks to be broken.

 

[gerryvz]

The reason is because the link points to a 126-related HOW-TO thread, before that forum was cleaved off of this one into a separate site.

There is a HOW-TO on this site now that specifically pertains to the E500E rear SLS sphere replacement.

HOW-TO: Replacing W124 Rear SLS (Self-Leveling Suspension) Spheres | "HOW-TO" Tutorial Articles

Starting around the May 2022 time frame (and possibly before), I noticed on several long-distance trips up to the NYC area, that the damping and bump-absorption capability of my E500's rear suspension was severely diminished. It was basically not absorbing bumps, and every time I would drive...

www.500eboard.co

 

[gsxr]

If you use the Search function, you'll find it... I see Gerry posted above as I was typing!

 

[MY911S]

Thanks apologies should have tried the native search.