![]() |
Self-Leveling-System - How it works, and troubleshooting the system
1 Attachment(s)
What does SLS Do?
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. Leveling Valve - the brains of the operation, it tells the system wether 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 leveling 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 leveling 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 leveling 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 leveling 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. Leveling 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 bouncys 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. Leveling 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 visable 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 leveling 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. http://people.oregonstate.edu/~lindg...ts_Diagram.jpg |
This should be a sticky somehow.
Questions come up regularly enough that would be answered by this. It also showcases that the system is not as complex as first glance would indicate, and that replacing with standard shocks should only be a worst case scenario. Black SLS fluid can also indicate bad accumulators or a very dirty system w/o pump motor oil leakage, too, in my experience. But if a pump is leaking, where are rebuild kits available for the seals? |
What type of oil does the system take?
|
1 Attachment(s)
Here is where I have gotten rebuild kits for the pump. He doesn't have a website, but he'll send you a catalog. He has lot of other MB parts and kits as well.
George Murphy Performance Analysis Co. 969 Oak Ridge Turnpike, Suite 258 Oak Ridge, TN 37830 865-482-9175 This is the fluid you want to use http://www.peachparts.com/shopforum/...1&d=1266268267 |
Wow, excellent write-up. Thank you.
|
Andrew has become the authority on these systems, which we appreciate!! :P
Andrew, I hope you source the large o-ring that seals the two halves of the hydraulic pump together. I have one that I can rebuild if I get that seal. The two halves just poured the fluid out, and the o-ring had flattened. That "half" seal isn't included in any of the kits out there..... |
Damp.
Not "dampen". The SLS only "dampens" bumps (or your driveway) if it is leaking fluid.
Jay. |
Quote:
|
Good timing as my wagon began sagging a little over night recently. The PO had extensive SLS work done years ago, so the only SLS repair I've had to do is replace the resevoir itself. Darn thing developed tiny holes all over and began leaking. The resevoirs are dealer only and cost more than $400, so if you see a good used one at a yard or elsewhere, might want to pick up a spare...
|
Awesome write up. Thanks. Does this apply to W123 and W124 wagons? Same system on both?
I'm looking forward to seeing mine in action towing and hauling. How much is the towing capacity for the W124 wagon? anyone know ? |
Different pump and valve on the two different models but in theory the systems work the same.
|
Quote:
|
Quote:
The Citroen and Rolls/Bentley versions are nothing more than metal cans with plumbing in the bottom and a cap + fitting in the top. Are they pressurized? They wouldn't seem to be. How much do they hold? |
Quote:
For instance, when my main pressurizing hose failed in the middle of nowhere and I was towing a trailer, everything worked fine (car was holding level with a heavy load) until I made the mistake of stopping at a gas station and letting everyone out of the car. The valve opened to adjust to the lack of load. When everyone got back in the car, the car sunk down and wouldn't pressurized back up again. The lesson is, when you know the pump is not going to be able to pressurize the system again, don't let the adjustment feature activate unless you are happy to let the system drop down to the bottom. |
Quote:
|
Quote:
Their failure is pretty rare; I'm probably the only one on the forum who has had to replace one. I don't know what caused the holes to develop but I suspect high desert heat and time. Used resevoirs can be found for $60 bucks or less. Salvage yards units would cost much less, but are rare in the yards as only w123 wagons and long wheel base w116's come equipped with SLS and use the same resevoir. I've only seen one in three years...on a euro w116 (450 sel?) with the coolest creme green velour interior; but didn't have the proper tools to get it off... :mad: |
I just replaced the accumulators in my 1990 560 SEL last night. The ride improved dramatically, though I now have some leaks at the fittings. Hopefully all that is required is a tightening.
|
So if I unscrew the cap and lift it out a bit, I should be able to see fluid circulating back into the reservoir while the engine is running?
|
Quote:
|
pulled the cap off yesterday, i didn't see any flow...guess that's why my rear was sagging...i was pulling a trailer. the fluid level is full. today the rear seemed level, but i dropped the trailer last night. I wounder if the pump is shot?
|
Quote:
|
Hi, I'm new here, but i've been reading this forum since I have my W123 300TD. I am also sorry, if a similar problem has been discussed before.
The thing is - I have changed both the accumulators and the SLS valve (a tested used one) - my car does rise up as it should and the ride is not hard, nor bouncy - the only problem is that it sags overnight. The symptom, which I find uncommon, is that after the engine is turned off - I can hear a noise of something loosing pressure - like a tire deflating - could this mean that everything is working fine, only there is a loose connection in the system? I just wanted to make sure, before rebuilding the pump/changing springs/struts. Maybe you could advice on the next step. Many thanks. |
The hydraulic shocks come to mind. Do you notice any moisture/leaks around the spring perches?
|
Quote:
|
If only it were so cheap and easy with the T124.
|
Quote:
Biodiesel300TD {Andrew} sells rebuild kits for the W123 300TD, with instructions. And pictures!! I've purchased 4 from him I believe. A great person to do business with!!! Have no fear! |
Thanks, guys.
I'm guessing, that it could be the struts, but since those are so expensive, I'll do a valve rebuild. |
If it was the struts youd be leaking. Its the valve.
|
300td wagon with hibernating SLS...
Hi:
Rear suspension has been low on my list of priorities. The car's rear has been riding low all along, but drives ok by my standards. I looked in the SLS fluid reservoir the other day and learned it was empty. When I do fill it, I'm prepared to find some sort of leak. What are the chances that the pump and valve and accumulators are still functional, given that the system has presumably been critically low on fluid for several years? Thanks in advance for your thoughts! Cheers, Brad |
The chances of the pump still working are minimal.
|
The valve, accumulators, and struts are probably fine, but the pump may not be. It runs no matter what when the engine is running, so it may be toast. But I'd get some mineral oil and fill the system and see what happens. The system is self bleeding, so you just fill the reservoir and start the car and keep filling it untill it maintains between the marks on the res. Run it for a while. And keep any eye on the fluid and watch what the rearend is doing. If you get no raising at all then the pump is not doing it's job anymore.
|
SLS removal/install proceedure
Great post and info!
I am looking for the proper removal/install proceedure for the SLS pump on a 1988 560SEC. I have the repair kit already. I could probably just wing it but would rather it were done by the book. Does anyone have some thoughts? Thanks! David |
I'm not familiar with that engine, but I'm sure someone here with the 126 FSM could post the pdf for you.
|
Thanks....I will start a new thread with the same question.
|
Thats a wise idea, you'll likely get more responses that way. Welcome to the forum by the way!
|
My experience with SLS
Purchased an '82 euro td wagon with sagging rear - pump was replaced at some point but reservoir dry! I filled system and had some results but then noticed accumulators were shot, replaced those and voila! Also replaced SLS valve with used valve and linkage arm and adjusted to neutral position. I then measured center of wheel emblem to fender lip and noticed slow settling overnight but as I drove car, it seemed to improve. I added a seal conditioner (non petrol based) to swell any dry seals and so far, things look great! I am not a big fan of "mechanic in a bottle" but I have had several successes in the past and thought I would give this a try. I will most likely flush and refill in a few more months as fluid is over a year old and I want to see if I can maintain cleaner looking fluid as a result of a better sealed system. SLS is fairly simply but I can understand why it people run from it as components are expensive. One member sells SLS valve reseal kit with great instructions - my struts appear to be in great shape and ride is wonderful versus the drive home when I first purchased this wagon -my experience, thanks
|
Possible to clamp off flex lines near the struts...?
Hey Biodiesel300TD,
Thanks for the advice. There aren't any external leaks and the system did raise the rear end. I'm fully expecting, however, that the system is probably leaking hydraulic fluid into the crankcase oil. (This would explain the previous I'd love to sacrifice the self-levelling and just maintain pressure in the struts and/or accumulators. Anyone ever heard of this working or have ideas about methodology? Finally, is the addition of the hyrdraulic fluid harming the lubrication qualities of my engine oil? (79 300 td) Thanks, Brad |
Quote:
http://www.peachparts.com/shopforum/diesel-discussion/292649-sls-without-pump.html Also, the valve can leak internally allowing the rear to sag over time, and you'll never see a drop of fluid. So if you are seeing sagging it could be do to an internal leak. But since your res was empty it's likely going into the motor oil. I don't know the specifics of hydraulic fluid, but it is most likely not a good lubricant. Keep an eye on your fluid and see if your loosing any. |
Is it the same pump as used on the 190E 16? If so I have a used one.
|
It is mentioned above that the system self bleeds. Most of this talk is about the W123. Does the W124 also bleed like this? If the bleeding process is automatic with system operation, what is the bleeder on the top of the SLS valve for?
I just replaced my accumulators and am looking for what else I need to do to get the system functional. |
That bleed fitting is probably there just to bleed pressure of the system in order to work on it. Same as the 123.
|
Hi,
I´m having a problem with my SLS. The car rises whem fully load, everything works fine. Except when I hit a bump or something similar. It feels hard, it´s like when we ride with bad shock in front. The springs go down but it´s not smooth. What could it be? Bad rubber bush? The Shock? The accumulator? The Valve? Thanks in advance Vasco |
Quote:
|
Quote:
I never really though about it before but it's funny that the same part can result in two different very symptoms when it goes bad. Hard ride or really bouncy ride. They must fail in two ways. Not sure how though.:rolleyes: |
Quote:
|
I appreciate very much all you replies. J
The car in question is an 1988 S124 200TD. It feels strange being the accumulators because I change them 100K ago. Before I change them the ride was very bouncing, if you had a ball in the trunk it will hit the roof. Now doesn’t bounce, but feels hard, you can feel every bump on the road, even a small imperfection. It´s banging quite loudly over bumps! I´m gone to check the accumulators. J |
Quote:
|
Ok! Thank You!
I Will check that. |
I’ve notice, when loaded, it doesn’t "bang" as loud as empty.
|
I´ve check the rear axle, and found that a suspension arm is kaput.
Thank You! |
All times are GMT -4. The time now is 07:27 PM. |
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2025, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website