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Biodiesel300TD 02-15-2010 02:12 PM

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

UriahT 02-15-2010 02:55 PM

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?

marfa300td 02-15-2010 03:31 PM

What type of oil does the system take?

Biodiesel300TD 02-15-2010 04:11 PM

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

POS 02-15-2010 07:02 PM

Wow, excellent write-up. Thank you.

JimmyL 02-16-2010 12:34 AM

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.....

babyjames 02-16-2010 02:07 AM

Damp.
 
Not "dampen". The SLS only "dampens" bumps (or your driveway) if it is leaking fluid.

Jay.

Biodiesel300TD 02-16-2010 10:53 AM

Quote:

Originally Posted by babyjames (Post 2406654)
Not "dampen". The SLS only "dampens" bumps (or your driveway) if it is leaking fluid.

Jay.

According to the dictionary; it dampens the ride, but it can also dampen the driveway when it's leaking.

sd300td 02-16-2010 12:10 PM

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...

biopete 02-16-2010 05:10 PM

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 ?

kerry 02-16-2010 05:22 PM

Different pump and valve on the two different models but in theory the systems work the same.

johninva 02-16-2010 06:18 PM

Quote:

When the car is unloaded and sitting at the proper height the leveling valve is in the "Neutral" position, which allows the pressure that the pump is creating to just flow back into the reservoir without pressurizing any of the components.
I understood it that the springs combined with a base pressure through the valve in the neutral position maintained the unloaded ride height. what are your thoughts on that ?

strelnik 02-16-2010 06:30 PM

Quote:

Originally Posted by sd300td (Post 2406874)
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...

What makes these reservoirs so expensive?

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?

kerry 02-16-2010 06:41 PM

Quote:

Originally Posted by johninva (Post 2407089)
I understood it that the springs combined with a base pressure through the valve in the neutral position maintained the unloaded ride height. what are your thoughts on that ?

It's my understanding there is pressure in the shocks and accumulators when it is not being adjusted but the pump pressure is just being recirculated back to the reservoir.

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.

Biodiesel300TD 02-16-2010 08:11 PM

Quote:

Originally Posted by johninva (Post 2407089)
I understood it that the springs combined with a base pressure through the valve in the neutral position maintained the unloaded ride height. what are your thoughts on that ?

This is correct. My wording it kind of poor, I will change it. The pump is always creating pressure, which is just sent back to the reservoir when the car is in the neutral position. When the car is loaded the valve then sends the pressure to the accumulators and struts which expands the struts and causes the rear to lift until it hit the neutral position again.

sd300td 02-16-2010 08:58 PM

Quote:

Originally Posted by strelnik (Post 2407099)
What makes these reservoirs so expensive?

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?

Nothing more than supply and demand, I think. I don't remember their capacity (4-5 quarts?) but they're about the size of many washer fluid resevoirs, made of heavy plastic, basic cap with a metal return line attached and a small filter which resides in the neck of the tank.

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:

cherry_560SEL 02-18-2010 01:15 PM

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.

odie 02-18-2010 03:24 PM

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?

kerry 02-18-2010 03:31 PM

Quote:

Originally Posted by odie (Post 2408324)
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?

Yes. If you're going to do that much work, change the fluid while you're at it. Let the return line run into a container of some kind and feed fresh fluid into the reservoir.

odie 02-18-2010 04:35 PM

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?

Biodiesel300TD 02-18-2010 05:32 PM

Quote:

Originally Posted by odie (Post 2408401)
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?

Try starting the car and then have to adults sit in the back with the rear open and your feet on the ground. You can feel the rear lift, that is if the pump it working. If nothing happens then your fluid is low or the pump isn't doing it's job.

orians 06-08-2010 03:39 PM

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.

andrewjtx 06-08-2010 04:17 PM

The hydraulic shocks come to mind. Do you notice any moisture/leaks around the spring perches?

winmutt 06-08-2010 04:49 PM

Quote:

Originally Posted by orians (Post 2482837)
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.

Valve rebuild. Cheap and relatively easy.

babymog 06-08-2010 09:30 PM

If only it were so cheap and easy with the T124.

JimmyL 06-09-2010 12:15 AM

Quote:

Originally Posted by orians (Post 2482837)
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.


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!

orians 06-09-2010 10:01 AM

Thanks, guys.

I'm guessing, that it could be the struts, but since those are so expensive, I'll do a valve rebuild.

winmutt 06-09-2010 10:06 AM

If it was the struts youd be leaking. Its the valve.

bradley6 01-31-2011 03:07 PM

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

winmutt 01-31-2011 03:10 PM

The chances of the pump still working are minimal.

Biodiesel300TD 01-31-2011 03:19 PM

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.

DM198856SEC 02-08-2011 11:02 AM

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

Biodiesel300TD 02-08-2011 12:13 PM

I'm not familiar with that engine, but I'm sure someone here with the 126 FSM could post the pdf for you.

DM198856SEC 02-08-2011 12:16 PM

Thanks....I will start a new thread with the same question.

Biodiesel300TD 02-08-2011 12:22 PM

Thats a wise idea, you'll likely get more responses that way. Welcome to the forum by the way!

warmblood58 02-08-2011 04:49 PM

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

bradley6 02-09-2011 03:18 PM

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

Biodiesel300TD 02-09-2011 03:33 PM

Quote:

Originally Posted by bradley6 (Post 2658538)
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

Here is a thread where we were talking about doing away with the pump and just sealing the system up. No real definete answers but some ideas.
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.

babymog 02-09-2011 06:17 PM

Is it the same pump as used on the 190E 16? If so I have a used one.

Renntag 02-21-2011 07:04 PM

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.

kerry 02-21-2011 07:14 PM

That bleed fitting is probably there just to bleed pressure of the system in order to work on it. Same as the 123.

Vasjor 11-23-2011 07:16 AM

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

kerry 11-23-2011 09:22 AM

Quote:

Originally Posted by Vasjor (Post 2833622)
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

Accumulators. It's almost always the accumulators.

Biodiesel300TD 11-23-2011 11:03 AM

Quote:

Originally Posted by kerry (Post 2833684)
Accumulators. It's almost always the accumulators.

I second that.

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:

Orv 11-23-2011 03:43 PM

Quote:

Originally Posted by Biodiesel300TD (Post 2833729)
I second that.

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:

What I've heard is when the diaphragm fails, initially the nitrogen mixes with the hydraulic fluid, forming bubbles that make the ride bouncy for the same reason your brakes get spongy when they need bleeding. Eventually the bubbles purge out and then the ride gets hard, because all the compliance is gone from the system.

Vasjor 11-24-2011 04:08 AM

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


Biodiesel300TD 11-24-2011 12:53 PM

Quote:

Originally Posted by Vasjor (Post 2834414)
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

If you're getting bumping or banging noises you might also check the sway bar links. They are S shaped things with ball joints on the ends that attach to the end of the sway bar in the rear. The ball joints should have boots and they joint should be stiff. If it's loose or wobble it's time for new ones.

Vasjor 11-24-2011 01:02 PM

Ok! Thank You!
I Will check that.

Vasjor 11-25-2011 05:25 AM

I’ve notice, when loaded, it doesn’t "bang" as loud as empty.

Vasjor 12-03-2011 03:36 PM

I´ve check the rear axle, and found that a suspension arm is kaput.
Thank You!


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