SLS problems.

[Espen W]

Hello everybody!

I have a 1991 S124, that I have been working on for about a year now.
I am experience some weird problems with my SLS system. I have been testing, replacing and wrencing allot. I have also been in contact wit many people. Proffesional MB mechanics, gurus and several of the guys in the MB clubs I am member of here in Norway.

This is a 230 TE (M102) Cam shaft driven pump. Same pump found in W201.

The problem:

- The car rises ~2" above "spring height" in the rear and gets harsh and have an aggressive rebound.
- I can manually operate the lever arm on the valve, and rise the car.
- I can maually operate the lever, and get the car back down, but not all the way down, so it can rest on the springs.
- I have been doing all kind of bleeding, oil replacement etc.
- I have the 124 WIS CD, and have been following all procedures and read all technical information I have managed to dig up.



I have replaced:

- Axle seal and o-ring in the pump.
- SLS valve (tested several new and used valves)
- Small piping from valve to air cells
- Air cells
- Large piping from Air cells to damper hoses
- Damper hoses
- Dampers
- Springs

All original or OE parts. Febi oil, with same number found on the oil tank.

My main therory have allways been the the return lines have reduced flow rate.
I have been using pressurized air, I have used bicycle shifter cables on a cordless drill threw the lines, but there is nothing in there. They are open.
The oil returnes to the tank in rich amounts. If I force the trottle, more oil retures to the tank.

If I open the bleeding niple on the SLS valve, oil comes out, and the car is back down on the springs, but as soon at the engine starts and the system is up and running, the rear end rises and gets harsh.

Everything looks fine, all parts are replaced, but there's something wrong.

I have one observation. Every 20 seconds, I can hear a "clunk" sound in the system. This is a pressure spike. I can feel it, if I hold around the first pressure hose attached to the pump.

Replacacing the seals in the pump was the last thing did, and after that, the spike is harder and I can actually hear it inside the car when I drive.


This is not funny, I am so tired of this. My lovely car is not good on the road.


All kind of answers and/or tips are highly appriciated.




Please note. Car looks ok on this pic, but I have rubbers with one extra knob in the front, and one less in the rear. Just to try to balance, and have some light a litle more than 3 foot in fron of the car.



Espen

[hookedon210s]

Are you sure the rod connecting the SLS valve to the anti-sway bar is adjusted correctly? The SLS suspension for an unloaded vehicle should be in "neutral" until the rear is depressed 1.5 -2 cm or so. If I recall correctly, making the connecting rod shorter will delay the action of the SLS. Good luck. Mark

[Espen W]

Thanks for your reply.

This problem is not about adjusting the conecting rod. I am not able to bring the car back down to neutral, resting on the springs.

And, the rod must be longer to delay the action.

Thanks anyway.


Espen

[hookedon210s]

If you open the return line on the SLS valve does the suspension settle? Mark

[Espen W]

I'll try that again.

I have made one attempt with a regular hose barb and a vinyl tube, all the way back, but it melted down because I fixed it too close to the KAT.

I will try to make a better hose test. With a SS braided PTFE hose, all the way back to the tank.


Again, thanks.



e

[hookedon210s]

I know you said that you have tried various SLS valves with no difference but... The SLS level valve has a pressure holding feature which ensures that the hydraulic struts, etc. have the proper pressure. I replaced my SLS valve in my 300TE after replacing the accumulators because the strut damping was inadequate. No issue with ride height however. The pump only feeds the high side (not the return line) and is self-limiting so I wouldn't think that could cause a restriction in the return line. Have you tried driving the car with the rod disconnected? Mark

[Espen W]

Yes, I have been driving the car without the rod.

From what I can understand, the SLS valve regulates the return flow, and there must be some kind of check valve that holds the car when the engine is not running.





I have been thinking about that there could be pieces of old accumulator-membrane somewhere in the return line.

The factory shaped return lines are not available anylonger. The lines have been replaced by "to be adapted during assembly" lines.

I have been bending brake lines in the past, and this is not a funny job, even with proper tools.

I want good looks and perfect function.

The subframe must down (again), etc, so this is a job.



e

[hookedon210s]

I have been thinking about that there could be pieces of old accumulator-membrane somewhere in the return line.

Have you completely flushed the system including emptying the struts? They may be acting as a reservoir for pieces of the membrane which may quickly plug the pressure holding valve/return orifices in the SLS valve. It is hard to imagine that pieces of the membrane could block the return line but I suppose it is possible. Have you tried disconnecting the return line at the SLS valve and back-flushing the return line? I recently replaced the accumulators on my 2001 E320T and was surprised to see pieces of membrane flow out of my left accumulator. I had not had this happen before and would not have believed it if I had not seen it. Since this was the case, I supported the the rear control arm, disconnected the strut from the control arm and pumped the strut several times to (hopefully) remove any impurities. No problems so far.

It is amazing how good the system is when it is working properly and how it slowly deteriorates over time until you finally conclude that the accumulators need replacement. Truth is, they probably needed replacement 20K miles before (my car has 115K miles).

[Espen W]

Sorry for not responding, but I have been on holyday for a week now.

I bought the car with 145K miles, and I am pretty sure it had the original (and blown) accumulators.

Next project must be to clean and flush the WHOLE system.

Good working SLS is a dream! My system works fine when adding weight.
A couple of weeks ago, I helped a friend transporting beer for his 40' anniversary.
I guess I had 8-900 pounds in the trunk. I can tell you the car was pretty low in the back. Started the engine, and the car was levelled within 10 seconds.


Again, thanks for your help.



Espen

[hookedon210s]

No problem---we have to live our lives and do these mundane things in our own time. Properly functioning SLS is indeed a worthwhile dream. Mark

[Espen W]

And now I understand what you said here.

The pump only feeds the high side (not the return line)

Maybe the 3q "sinter filter" can be blocked by old pieces of accumulator membrane. This makes sense.

I't so good to find out a litle more.
This problem have caused me so much frustration.

Again, thanks Mark.


Espen

[hookedon210s]

I helped a friend transporting beer for his 40' anniversary.
I guess I had 8-900 pounds in the trunk.

Sounds like a nice party and you are a good friend!

The only problem with the SLS is it will pretty much support whatever you can load into the car. I once loaded oak hardwood flooring into my W124 1/4 meter higher than the bottom of the windows---it must have been 650kg or more. The car rode level but I had to replace the accumulators shortly thereafter. Mark