I've narrowed down my innoperable SLS system, I think, to the SLS pump.

I have been getting non-stop bubbles out of the bleeder port while trying to burp the system after rebuilding the valve and pump.

The pump itself appears to be the source of the bubbles - I disconnected the high pressure line from the pump and fed it directly into the reservoir. After starting the engine, the fluid flows steadily but is filled with small bubbles. I can see the bubbles clouding up in the reservoir as it is being refilled from the high pressure line. So does anyone have any experience with this? The simplest explanation seems that there is air being sucked in either from one of the connections on the suction/return line to the pump or from some seal in the pump itself. I did just rebuild the pump, so could it possibly be that one of the seals didn't align right, or is this a sign of a pump at the end of its life? Any insights ?

The system is self-bleeding so if it's working right it should sort itself out. I've never taken the high pressure hose off the pump and fed it into the reservoir so I don't know if it normally pumps bubbles.

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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

Hey, thanks for the reply. I have read that it was self bleeding. I drove the car about 140 miles the other day and hoped that it would, in fact, clear itself out.

Throughout the drive, the suspension did dampen out the bounces. However, it stayed low and would not really rise up with vigor when revving or even after adjusting the lever manually.

That is the point when I opened the bleeder on the valve and bubbly fluid flowed out. I refilled the reservoir several times from the fluid that was bled and still, the fluid was never really clear of bubbles.

When bleeding directly from the pump, I saw a continuous stream of much smaller bubbles. I did shut off the engine for a while in hopes that the bubbles would dissipate and to see if that would clear it up, but after starting again, the pumped fluid continued to appear with the entrained bubbles. I'm thinking air is getting in somewhere, perhaps a bad seal in the pump or something. I don't want to rebuild again if it is in fact something simpler or if the pump is bad in the first place. Any other thoughts?

Try cracking open the high pressure banjo bolt on the SLS pump while the engine is running. Close it shut when no more air bubbles escape.
This may remove any air in the pump.

Not directly related to repair of your issue, but getting rid of the SLS on the wifes wagon was the best decision I've ever made FWIW.

A viable option if you just get sick of endless rear dragging and diagnosis. Went from worrisome to a non issue

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From what you've written, I take it that the rear end has never raised up as long as you've owned the car. Is that right? What is the reason to exclude the valve as the cause of the problem? I also take it that you have gotten under the car with the engine running and manipulated the adjusting lever manually and the car has not risen up? I'm not entirely sure of the physics of air bubbles in the system but I'm thinking that if the valve is working and without a heavy load in the car, even fluid with air bubbles should raise up the rear of the car if the valve is working correctly.

__________________
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

There are 2 steel balls in the switch, a big one and a little one.
You did install the big steel ball back in the switch didn't you?
For some reason there is very little ever mentioned about it on the websites
And it's exact function and placement.

I just rebuilt my switch and before I did I had air bubbles.
With the switch rebuilt I now have a steady stream of fluid and a
Working SLS system.

Thanks for the responses. I did take off the pump to have a look at the seals and all was good - I had rebuilt it only a hundred miles earlier and the o-ring and seals looked good. I hand turned the pump with fresh fluid to try and prime it, and I put thread sealant on the return line into the pump, but after reinstalling the pump, I still got the small bubbles out of the high pressure line.

Then I thought that maybe it's not a big deal - perhaps the bubbles don't appear when the fluid is under pressure, and that maybe it is only appearing because of the low pressure environment that's created by draining the high pressure line into the reservoir. I took a look at pump prices on ebay and decided to go with this idea. I then decided to go ahead and try bleeding the system again using a different method.

Before I went to rebleed the system, I did as Rockyriver suggested and took a look at the valve. All the parts were there. I just reassembled it again, paying attention to the the large ball bearing's location. Apparently, the large ball bearing should be situated towards the middle of the valve before reassembly. When I previously rebuilt the valve, I'm not sure I payed attention to where it was before inserting the valve's pistons/ springs (see here for more on that.)

So after reassembling the valve and reinstalling on the car, I did a quick check and bled system. The fluid came out with some bubbles at first as before, but then shortly after it was almost clear - this was encouraging.
I then did a full bleed operation. This involved loading the back of the car with 300+ lbs and jacking up at the differential till the wheels raised up. (All this was done with the engine running.) When the weight was off the rear wheels, I opened the bleed nipple and then lowered the car to rest again on the wheels (using wheel ramps, of course). I then closed the bleed nipple after the car settled at the bottom of travel and repeated. I got a plume of bubbles near the bottom of travel for the 2 or 3 times I did this and then figured that was enough to clear the majority of air from the tops of the struts.

I removed some of the weights in the rear to roughly equal a full tank of diesel and then reset the distance on the little linkage arm and bolted it back onto the valve's height adjuster arm (which was set to the center position.) Took the car out for a couple miles drive. The rear seemed to be higher (I could see the horizon finally in the rear view mirror instead of just the roadway behind). Came back and measured the wheel center to fender lip in the rear ~ 13 inches on both sides. This is a big improvement - a full 2+ inches higher.

In the end, I'm not sure if the valve was initially assembled wrong, or if I needed to simply persist in bleeding using an efficient method. Also, if your rams / struts have ever been emptied of fluid, like mine were (I rebuilt the struts too), driving the car, alone, is not going to be enough to bleed the system. The method of jacking up and releasing to bleed the system really seems to be the best way to fully bleed to get back to functionality in the case where the struts have been emptied. I'm still not sure what the true reason for the small bubbles in the pump outlet - perhaps they all do this and I overthought it when seeing it. Anyways, now it all appears to work, so I'm gonna assume the pump's fine.

Update - I bled them again since this last post when I installed new rear coil springs. After a few up and down strokes with weight in the back and cracking the lines at the strut tops, I got rid of the bubbles. Looks like it just take a little extra persistence and patience. SLS system works great now - very subtle and smooth with an empty car.