SLS Valve Rebuilds:

On my 84 300TD wagon, about 3 years ago, I rebuilt the SLS valve at the rear of the car to fix the overnight sagging of rear end....it fixed the problem, but over the last 12 months the rear end sagging has returned.

I have an SLS valve from another car, and I installed new seals, and ready to replace, but I am apprehensive to do this since the SLS fluid gets dirty real fast.


SLS Pump Rebuilds:

About 18 months ago, I installed new seals in the SLS pump (mounted on the engine), thinking that engine oil must be getting past the seals. I flushed entire system with clean fluid, but the fluid gets dirty quite fast (in 2 to 3 months, it gets black). So, I thought maybe I didn't do the seals properly, or maybe I damaged the shaft seal....so I got the kit from ************** with directions, and 2 months ago rebuilt the pump again, meticulously following instructions, and replaced with new clean fluid, completely flushing the system. (when I flush the system, I do it over a few days, driving the car, to ensure shocks and air cells are flushed as well).

Now fluid is black again! I mean opaque black on the SLS reservoir dip stick!


So, my question is:

How long should SLS fluid stay clean....I assume that in any hydraulic system, the fluid should stay somewhat clean and clear over many months, maybe turning slightly yellow. But maybe I'm mistaken.....in this mercedes sls system, is it normal for fluid to turn black? I can only figure that it turns black because engine oil is getting by the shaft seal in the pump....the engine side of the pump is lubricated with engine oil, the interior of the pump is lubricated with hydraulic fluid. The only barrier between the two is that one shaft seal (lousy setup). I know that annual fluid change is recommended, but the way my system is functioning, monthly changes seem to be required.

When I rebuilt the pump, the shaft where the seal is looked very clean, shiny, not scored or damaged in any way.

So, bottom line, is it normal for engine oil to leak past the shaft seal, or do I simply have a worn pump....maybe there is an imperceptable wobble when the shaft is rotating, allowing engine oil to enter sls system.

Any thoughts?

Thanks much in advance.

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Are we sure that the only way the fluid can get black is from the engine oil? Could it be turning black from some substance leaching from the rubber diaphragms in the accumulators?
I discovered that replacing the accumulators solved the overnight drooping (mostly) without doing anything to the valve.
I don't consider overnight drooping to be a serious problem. It does put a load on the engine right away at cold start up but within about 40 seconds it's erect and ready to go.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

When I got my car I did not replace the SLS for almost a year. And odds are the PO did not replace it for while, although it had some new MB parts. It may then have been serviced. So for certain I can say it lasted a year and probably longer.

I replaced it because I thought it was bad. The tank looked very dark. But when I was pumping out the old to make room for the new the fluids looked the same. So the fluid was not bad or black, just looked so until I watch it pour into a container.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

I'm wondering if the high and/or low pressure rubber hoses leach black into the fluid over time. I can't seem to keep my fluid clear and I know I need to replace the hoses because they are seeping fluid.

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1981 300TD 310k miles
1970 280sel 172k miles
1966 230 Fintail 162k miles

"Where are we going? And why am I in this hand basket?"

If they are seeping fluid, you can bet they are deteriorating into the fluid. Change 'em!

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'85 300TD "Puff The Magic Wagon" - Rolling Resto
'19 Mazda CX-9 Signature - Wife's sled
'21 Morgan 3-Wheeler P101 Edition
'95 E300d - SOLD
'84 300TD "Brown Betty" - Miss this one
'81 240D "China Baby" - Farm grocery getter

They are next on the list, Tex!

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1981 300TD 310k miles
1970 280sel 172k miles
1966 230 Fintail 162k miles

"Where are we going? And why am I in this hand basket?"

If you're getting motor oil in the system the level of the SLS fluid should raise over time. It might be rather slow, but you'd still be gaining fluid. Thats assuming you're not loosing fluid the other way, putting SLS fluid into your motor oil.

Also I'm not sure you can completely flush all the old fluid out unless you too everything out and cleaned it and put it all back. It would probably only take a few ounces of old black fluid to turn all of it opaque black. If the system is working, and you're not loosing or gaining fluid I wouldn't worry about it.

Kerry I don't follow how the accumulators could fix your sagging problem. The accumulators as I understand it are for cushioning, and the struts actually raise and lower the rear controlled by the valve.

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I don't either. I have no explanation for it, but it certainly happened. It's not perfect and it still sometimes droops overnight but it was always doing it before I replaced the accumulators.

Now that I think more about it, maybe I do have an explanation. There could have been a microscopic hole in the rubber diaphragm that was allowing fluid thru slowly overnight and causing the system to lose pressure.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

the problem with that as a possibility, is eventually, the hole would fill the accumulator with liquid, and it would be not take on any more fluid. (the things only hold like 2 cups of volume... including the nitrogen....

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!