SLS Valve Mystery - Page 2 - PeachParts Mercedes-Benz Forum

nhdoc · #16 10-26-2009, 04:45 PM

Quote:

Originally Posted by Biodiesel300TD

The springs are supposed to maintain unloaded ride height, which also happens to be where the lever arm is level with the ground. But when the springs get tired they cause the rear to sag, which causes/forces the SLS system to maintain the unloaded ride height, keeping the lever arm in the level position. In a system with worn springs and no leaks the SLS system will maintain the unloaded ride height all the time. But if you have a leak in the system the rear will sag down until the springs are holding the height. Then when the car is started up the system pressurizes again and the rear lifts up.
With that said you can change the ride height using the SLS system, but you are causing the SLS to hold the unloaded height not the springs.

If your rear is settling with the rod attached, dispite what it does when it's not attached, the valve is leaking. It can leak internally which allows the SLS fluid to flow when it's not supposed to.

I think I now understand the comments about setting the arm level...you mean set it level when the system is not pressurized at all, being at the bottom of the range which is where the springs are supporting the rear end. That, in theory, should be the correct height unless the springs are worn/sagging. I always set mine up by using the SLS to maintain an acceptable height which was higher than that which is why I could not understand why you kept saying set the arm level since the arm is always level if the system is functioning.

nhdoc · #17 10-26-2009, 04:46 PM

Quote:

Originally Posted by kerry

There's have been lots of debates here about whether the hydraulic cylinders are designed to carry some load under all conditions. I believe the last post I read on this topic offered some kind of definitive statement on the issue, indicating that even with the car unloaded the SLS rams are intended to carry part of the load.

This was my understanding too...that's why I set mine up the way I did it, by using the arm adjustment to set the height.

nhdoc · #18 10-26-2009, 04:49 PM

Getting back to the OP, I agree with one of the other responses that the valve is leaking and regardless of why it only does it when the arm is attached is not really relevant, just the fact that it leaks down is evidence that the control valve is at fault (as long as no fluid is leaking out anywhere else).

johninva · #19 10-26-2009, 06:01 PM

man, this is getting confusing! All i think i know for sure is that even if the valve arm is in the release position, it should only release down to base pressure, not beyond base pressure. So if the rear sags lower that it should, there is a leak, in an accumulator, shock, internally in the sls valve or elsewhere.

I think normal ride height should be something like 13" from center of wheel to fender lip.

I think it is wrong to manipulate the lever to raise the unloaded ride height. Where it sets, running and unloaded, with the valve arm in the neutral position, is where you ought to set the length of the adjustable linkage rod to.

nhdoc · #20 10-26-2009, 06:32 PM

Quote:

Originally Posted by johninva

man, this is getting confusing! All i think i know for sure is that even if the valve arm is in the release position, it should only release down to base pressure, not beyond base pressure. So if the rear sags lower that it should, there is a leak, in an accumulator, shock, internally in the sls valve or elsewhere.

I think normal ride height should be something like 13" from center of wheel to fender lip.

I think it is wrong to manipulate the lever to raise the unloaded ride height. Where it sets, running and unloaded, with the valve arm in the neutral position, is where you ought to set the length of the adjustable linkage rod to.

The thing is "where it sets, running and unloaded with the valve arm in the neutral position" is wherever you set it to. I think what you are saying is "lower it to its base position and set the arm to level with the adjusting rod" because it will always "set" at whatever height you set it to when you install the adjusting rod to level the valve arm.

I don't think you can do any harm setting the height to some arbitrary level and installing the adjusting rod to set the arm level at that height. It would be the same as if you drove around with a load in the back all the time and parked it. There would always be pressure in the system fighting the load. Instead you are just fighting the weight of the car unloaded, but that's just my opinion...does anyone have a copy of the official WIS directions for setting up the valve? That would tell how the systems designer's intended it to be set.

johninva · #21 10-26-2009, 07:06 PM

Quote:

The thing is "where it sets, running and unloaded with the valve arm in the neutral position" is wherever you set it to. I think what you are saying is "lower it to its base position and set the arm to level with the adjusting rod" because it will always "set" at whatever height you set it to when you install the adjusting rod to level the valve arm.

with the vehicle running and the valve arm/lever in the neutral position and UNattached from the linkage, that should be the base ride height. thats how i understand it.

nhdoc · #22 10-26-2009, 09:38 PM

Quote:

Originally Posted by johninva

with the vehicle running and the valve arm/lever in the neutral position and UNattached from the linkage, that should be the base ride height. thats how i understand it.

The arm in the neutral position simply holds the level wherever it is set - if it is at the bottom of the travel then it is set there, if it is raised some then it is set there. It does not matter if the car is running or not - the arm being in the middle simply holds the height.

johninva · #23 10-26-2009, 10:07 PM

yeah, thats right. I guess what i mean is, say, with the linkage unattached, put the lever in the release position, the vehicle will settle to base ride height/base pressure in the valve and sls system. put the lever back into the neutral position. thats where/when the linkage should attach to the lever. If you have to manipulate the lever to raise the rear to get ~13" from center wheel to fender lip, with the vehicle unloaded, something is broke.

kerry · #24 10-26-2009, 10:47 PM

Quote:

Originally Posted by johninva

yeah, thats right. I guess what i mean is, say, with the linkage unattached, put the lever in the release position, the vehicle will settle to base ride height/base pressure in the valve and sls system. put the lever back into the neutral position. thats where/when the linkage should attach to the lever. If you have to manipulate the lever to raise the rear to get ~13" from center wheel to fender lip, with the vehicle unloaded, something is broke.

I believe that is false. If that were true, the rear end could never sag unless there was a load in the car. The hydraulic rams are designed to always carry some portion of the load. If you follow your method, with no load, the springs would be carrying the full load.

JimmyL · #25 10-27-2009, 12:41 AM

Andrew, your avatar change has completely thrown me off!

And I also miss the "hanger" sig pic with my favorite in the world 240D...

nhdoc · #26 10-27-2009, 06:48 AM

Quote:

Originally Posted by kerry

I believe that is false. If that were true, the rear end could never sag unless there was a load in the car. The hydraulic rams are designed to always carry some portion of the load. If you follow your method, with no load, the springs would be carrying the full load.

I've reviewed past posts and find there are these two schools of thought - one which says the SLS system should essentially be set so the system has little or no pressure unless the rear end is loaded (ie the springs set the ride height, not the hydraulics) and another which says you can set the correct ride height with the SLS system and rely upon it to maintain it. People in the first camp believe that if your car is below "correct height" without SLS then your springs are bad. People in the second camp disagree with this too.

Nobody has produced an FSM section to support either claim. I happened to be tinkering with mine yesterday anyway and I will admit until I read this thread I was in the second camp but now I am not so sure. I have not checked my ride height (yet) but I know I set it up using the SLS to carry some of the load because the car just looked "saggy" when it was at the bottom of its range. The key will be the measurement. I understand it is supposed to be around 12.5-13" from the center of the wheel to the bottom lip of the fender.

Mine does hold the height when parked though the control valve leaks a drop or two of fluid. It's funny because before I started tinkering it didn't leak so I suspect that it was originally set up with little or no pressure like those in "camp 1" believe. Then, I monkeyed with it and raised it up a little and now, because it is always carrying some pressure the valve leaks a little. Since it leaks very little I can live with it and I don't think setting the ride height this way does any long term damage since it would be the same as leaving a load in the back all the time would and there should not be any problem doing that with a system that is operating correctly.

nhdoc · #27 10-27-2009, 09:32 AM

I just checked mine and it is now set at around 13.75-14" which sounds high but is more or less equal to the front so the car is "level". If I set it back to 12.75-13" it will be lower in the rear than in front...don't know if that is correct ride height or not but it looks strange to be sloping back like that.

kerry · #28 10-27-2009, 10:04 AM

Quote:

Originally Posted by nhdoc

I've reviewed past posts and find there are these two schools of thought - one which says the SLS system should essentially be set so the system has little or no pressure unless the rear end is loaded (ie the springs set the ride height, not the hydraulics) and another which says you can set the correct ride height with the SLS system and rely upon it to maintain it. People in the first camp believe that if your car is below "correct height" without SLS then your springs are bad. People in the second camp disagree with this too.

I thought there was a definitive post in the last year or so which resolved the debate in favor of the second camp???

nhdoc · #29 10-27-2009, 10:32 AM

Quote:

Originally Posted by kerry

I thought there was a definitive post in the last year or so which resolved the debate in favor of the second camp???

I have not found it (yet) but if it does exist could you post a link to it?

I think the only definitive answer is found in the FSM procedure for setting up the system...unfortunately I do not have it!

I'm OK with setting it up the way I have mine...it doesn't move when parked for several days - just a drip or two of fluid will come out of the control valve. Like I said, I don't think you are doing any harm setting the height this way because it is the same as leaving a heavy load in the car and setting it up the other way would be. In fact, because you are relieving some load on the springs they will probably last a little longer this way.

Biodiesel300TD · #30 10-27-2009, 11:21 AM

Quote:

Originally Posted by nhdoc

I think the only definitive answer is found in the FSM procedure for setting up the system...unfortunately I do not have it!

I was reading through the manual last night trying to figure it out. I couldn't find anything that specifically said wether unloaded height is regulated by just the springs, or the struts and springs together. I will look some more tonight.