I was wondering if anyone out there had any ideas on how to test the MB SLS system components WITHOUT the need to install them?

By analogy, I can test a mechanical diesel fuel injector by test popping it with a pretty simple contraption made out of a bottle jack, a guage, et cet.

As for the W123 SLS system, Is there a way to test, for example, the pump? Or, the rear sway bar actuator? Or, the rear SLS struts?

Same issue relative to a lift pump?

Any ideas are welcomed. I was thinking of creating a fixture with a motor which spins the pump and setting up some gauages, et cet., with hook-ups to the various components. However, beyond that, I am stumped as to how to "test" to see if the components are working.

The hydralic rams should not leak under pressure around 200 psi?
Accumulators should not leak or the vechile will bounce like it has no shocks.
The valve is modulating and should not leak.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

If I hooked up the SLS pump, for example, and spinned it at 1,500 RPMs, how would I know it is pumping correctly? I could visually inspect the no-leak, but I suspect at 1,500 RPMs, I should have a certain PSI? Same with the rear sway bar actuator? Assuming no leaks, but how would I test it. Same with the struts ... assuming no leaks, but how could I tell its functioning?

By analogy, an injector may "lose" fuel under pressure, but that does say or mean it is popping correctly (spray pattern) or popping at the correct pressure.

Dead head pressure should be able to overwhelm the acccumulator pressure by a significant margin.

The accumulators should have be pre pressurized. This pressure can be measure as the pressure required to start pumping fluid into the accumulator.

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www.kiva.org It's not like there's anything wrong with feeling good, is there?

I never found the pressure but I believe it is around 150-200 PSI


First a little explanation of the Self-Levling-System suspension in the rear. The Self-Leveling-System(SLS) adjusts the ride height of the rear end when it is loaded to keep the rear end at the proper riding level. The springs and the SLS maintain the unloaded height. The SLS maintains height when loaded by pressurizing the system which lifts the rear. The springs, struts, and accumulators work together to dampen road bumps.
The system is made up of several parts, there is a diagram at the end of this post that shows all the parts. Here are the main components and what they do.
1. Pump - supplies pressure to lift the rear.
2. Fluid Reservoir - for maintaining fluid level.
3. Levelling Valve - the brains of the operation, it tells the system whether to lift or lower the rear end.
4. Accumulators(pressure reservoir) - Helps dampen the changes in pressure due to bumps on the road.
5. Struts - Works much like a normal shock for dampening bumps but is able to be adjusted by pressure from the system to change the ride height.

How it all Works?
The pump is always creating pressure and pushing fluid through the system. The levelling valve maintains the level of the rear end. It does this by maintaining pressure or diverting it to raise or lower the rear. When the car is unloaded and sitting at the proper ride height the levelling valve is in the Neutral position. In the neutral position the struts and accumulators are still pressurized which maintain the unloaded hight along with the springs. The valve maintains the neutral position pressure in the struts and the accumulators by not allow the pressure to bleed off and also directs the pressure that the pump creating to back to the reservoir. When a load is put into the back, the lever arm on the valve is deflected into the Fill position which which diverts the pressure and fluid flow to the struts and accumulators. This pressure expands the struts which lift the rear until the lever arm is in the neutral position again, a check valve in the levelling valve keeps the increased pressure from bleeding off until the arm is deflect into the Return Flow position. When the load is removed, the arm on the levering valve is moved to the Return Flow position which allows the increased pressure in the system to drain off, until the valve returns to the Neutral position and the rear of the car to it's normal unloaded ride height.

Now Some Troubleshooting-

Failure - Symptom
Pump failure - Rear doesn't rise when loaded.
Levelling Valve failure - The rear settling or sagging after sitting for many hours, and in extreme cases the rear doesn't rise when loaded.
Accumulator failure - Rides bouncy and/or hard, rear bounces like when you have bad shocks.
Strut failure - Rides bouncy but not hard.

Diagnosing a failed part
Many of the problems that arise in the SLS are caused by leaks, so the main thing is to look for leaks.
Levering Valve - This valve is located just in behind the rear axles and differential, slightly on the drivers side. The valve can leak internally, in this case you won't see fluid on the valve. It can also leak so there is visible moisture on the outside of the valve. If it is leaking I have available a o-ring kit to solve the leaking problems. Visit here for more information - SLS Valve O-ring Kit Info - Also make sure to visit the DIY on replacing the O-rings - O-ring DIY
Accumulators - Diagnosing this isn't as easy, the accumulators have a rubber bladder in them, with suspension fluid on one side and gas on the other. They can get holes in the rubber and then the fluid gets into both sides and the accumulator is shot. By poking the eraser end of a pencil into the accumulator you fan feel around the diaphragm for a tear. The pencil should only go half way into the accumulator. If there is a tear in the diaphragm you'll be able to poke the pencil all the way in.
Struts - Struts aren't often the source of problems with the SLS, the rarely go bad. But when they do the usually start to leak, so they will have suspension fluid on them and they shouldn't.
Pump - The pumps general don't break they usually start leaking. They leak internally usually, and cause one of two things to happen. They allow engine oil to be introduced into the SLS system, or they allow the SLS fluid to go into the motor oil. If the SLS fluid in the reservoir is black it has motor oil in it, or its really old fluid. Either way it should be changed. If you keep loosing fluid but it's not leaking anywhere else then it is going into the motor oil. Either way you've got to rebuild the pump. There are kits available for this. The other thing that can happen associated with the pumps are the hoses. There is one going from the reservoir to the pump and one going from the pump to the levelling valve. Make sure they aren't leaking. The one going to the valve is high pressure so if it gives out you'll have a big mess on your hands.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

150-200 PSI ... that's it?

I guess I will tinker this weekend and figure out a way to spin the pump 1,000-1,500 RPMs and see what the PSI is.

I will try to find something in the FSM on PSI specs. I know the W116 uses the same exact pump and that pressure is over 1,000.

I guess there are only 2 specificaition parameters:

1. No leaks
2. PSI or PSI maintained at a certain RPM.

I guess the same goes for the other components.

That's it but verify pressures. Also the control valve by the rear diff has a control arm when moved changes the pressure to the hydralic rams.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

According to my 126 Manual SLS pressures are in the range of 120 -180 bar! The official tester gauge has a 250 bar range, so closer to 1500 - 2000 psi range

Started the tinkering phase before Easter kicks in. This is what I was thinking. PLEASE comment, and be nasty, brutish, and short if I am headed down the wrong road.

I imagine a fixture mounted on some 1/4" aluminum plate. A mounting bracket for the SLS pump. An electric motor to spin the pump. Some hydraulic lines with a gauge, presumably up to 3,000 PSI. Some valves. A fluid resevoir, most likely from MB. A line then going to the SLS actuator which I can manually manipulate. Then, a mounting and a brace to hold a rear shock and something to put a load on the shock. I've sourced the O-rings for the rear shocks, but still looking for the nylon insert. I doubt that wears out, but since I am rebuilding everything, I might as well rebuild and replace everything. The only remaining piece of the puzzle is whether or not there is a method to carefully cut the nitrogen spheres in half, install threads to the halves, and rebuild them just like the Citreon spheres. The Citreon's are about the same. I need to measure them. Getting the rubber diaphragm sourced "appears" pretty simple. The jig to disassemble a Citreon nitrogen sphere looks incredibly easy to make. I am thinking of buying at least one to copy kat for MBs.

I have zero knowledge of this system but I'll ask the question anyway: Is there some VOLUME that has to get pumped in a certain time frame? I know that some hydraulic systems can provide adequate pressure but not move enough volume to satisfy whatever the pump is supposed to operate.

Also - when the heck are you coming this way!!??

Dan

On the pump, I'd think there is little chance of failure of the pumping parts and an examination of seals would tell most all of what you want to know....I don't know though, just a guess.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Hi Dan & Tom,

I'm headed Monday night to Ridge Runner's (Jim's) hopefully, and maybe meeting another forum member. I do need to head your way Dan. Two bad discs in my neck and the fear of a two level ACDF has curbed my hobby lately to some degree.

From what I can find and forum members' comments, I am guessing there is only two things to look for:

1. Leaks
2. An ability to build a certain amount of pressure.

I am guessing MB must have had a way to test these components before installation.

Bummer about the discs, Mark! Hope they don't prove to be a long-term problem.

You're welcome any time! Bring your 617 pump timing goodies and we'll see what a little more timing does, performance-wise. Mutt has pretty good access so I don't think we'll have an issue hooking everything up and I'll do the wrenching if you'll do the pointing so it shouldn't stress your spine.

Dan

Have you read the FSM for the test data yet?

(I can link if you need)

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1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I suspect MB engineered the components to function and meet design parameters, there may be some quality control in the supply chain but I highly doubt new, properly manufactured, properly specified individual parts would require any testing before installation!

There are both MB specified test tools and procedures for diagnosing malfunctioning systems in the official MB factory service manuals, that are useful for people working on repairing these systems.