Rebuilt SLS Pump -- Still not pumping
 

My 1982 300TD had a saggy rear since I bought it. Reading this post led me to believe it's a fault pump. Before I spent ~$1000 on a new pump I thought I'd go about trying to fix my existing pump.

I used the SLS rebuild kit from the place in AZ and replaced all the gaskets I could find. One medium, thick gasket remained (any ideas where that's supposed to go?)

While the pump was off I drained the reservoir tank and refilled it with ISO 46 hydraulic fluid.

I reattached the pump and started the car. The rear didn't raise and I opened the reservoir and didn't see any fluid pumping.

Any ideas? I have a new SLS filter that I was going to put on once I verified the pump was pumping. Maybe it's clogged? I'll replace it in the morning and report back.

I'd crack the high pressure hose banjo fitting and see if anything squirts out.

On a side note first, are you sure you have the correct fluid? The wrong fluid will destroy your accumulators. Hydraulic oil is no good. The proper stuff is expensive but only it works. If you have the wrong fluid, you will need to completely empty the system, flush it out a couple of times & then refill with the correct fluid.

There is a DYI about sls, I see you have looked at Andrews thread.
If you disconnect B1 you should have fluid flow with the motor running.
If not, you need to investigate why. Probably an air lock or blockage in the oil supply
Could you turn the pump by hand before you put it back on? A seized pump will damage the drive to it.
These pumps seldom give trouble. If you have assembled it just the same as you disassembled it, all will be good.

To raise the back a little, when the system is working, you can make an adjustment to the threaded rod that controls the sls valve from the anti roll bar.
My guess is that your height problem is probably failed accumulators, was the car very bouncy in the back?
The sls valve down the back would be my next suggestion, Andrew (the author of that thread) can supply you with a kit of O rings & instructions, dont bother trying to save a few pennies by buying individual O rings, his kit works & his experience & instructions are more valuable than the O rings.
If it does turn out that you have a failed pump, I would try & get one from a junk yard.

That's what I'm trying to do. Other threads have said that ISO 46 tractor hydraulic fluid is acceptable for testing. Once I've verified everything is working I'll be switching over to FEBI.

The pump is self bleeding, is it not? I think I read another thread where it took awhile for the air to bleed out on it's own. Maybe I need to wait awhile before worrying.


Yep. Made a pumping sound. :)

Already have a repair kit in my toolbox. I'll rebuild the valve once I know the pump is working.

Thanks!

It may take a while of running to get all the air out of the system. Lots of nooks and crannies for air to get stuck. You might have to drive it some to get all the air out. I know the valve is self bleeding because of the pump, but I'm not sure if the pump is self bleeding or not. In this case you may have to open the bleeder on the SLS valve with the car running to bleed the system.

The pump is always pumping fluid through the system, the valve is what controls the height. So you should always have fluid returning to the reservoir, that is, if the rear is not changing height at the moment. Check to see if you have fluid flowing into the reservoir, the return line is in the cap.

There is still the possibility that something's up your valve or the linkage. The valve is what really tells the rear what to do. If it's not functioning properly then the rear isn't going to do what it's supposed to.

No motion in the reservoir. Hopefully it will bleed itself out.

I'll check the banjo nut and report back.

there's air in the pump vanes... oil needs to get in there first for circulation to take place. :)

The Febi stuff is ISO-46 with die. The MSDS for both fluids is identical. In this case you're OK. On the other hand, there are a multitude of hydraulic fluids out there, some of which are glycol based (as in brake fluid). These are NOT compatible and will destroy your system ($$$$).

For all the hype surrounding it, the SLS system is incredibly simple. It's far, far easier to deal with than your average tractor hydraulic system - even the one on my 1950's Ford NAA. All you have here is a reservoir, a pump, a valve, two actuators and two accumulators which are nothing more than the "gas" part of a gas pressurized shock absorber. If you google "mercedes self leveling suspension" you'll find tons of info there.

The problem you're having with your pump is that you need to prime it. Try raising reservoir above the pump and let gravity do the work. You'll want to flush the system, so you'll want to let whatever comes out of the return line go into a separate container for recycling. Run at least half a gallon through there - as someone works the valve from underneath (the car should be up on ramps or on a proper rack for that!).

When you're done you can put the Febi stuff in there if it makes you feel better - but you'll need several liters in order to flush out the ISO-46 or the color will be wrong.

Thanks, now the pump is pumping and I see fluid coming through the filter in the reservoir. The back isn't raising yet so I'm off the check the valve.