Need a good diagnosis procedure - 300td SLS
 

Hello All, finally bought a beautiful wagon which needs SLS work. I have searched this site but have not found a step by step procedure for properly working through the SLS system to determine which area is at fault. Is there a 123 td wagon site? Any other tips/resources would be greatly appreciated, thanks!

I think the general diagnostic principle followed on this site, is that if the 'shocks' are not leaking and the height is correct, but there are ride problems, it's the accumulators.

thanks! Does anyone have a pic of the accumulators? I was hoping for a step by step diagnostic that also orients me to the system -thanks!

If you search on it there are pictures of accumulators cut open so you can see how they work. Spherical objects mounted to the body above and to the inside of the rear lower control arms with metal lines and rubber hoses going in and out. It's a pretty easy job to replace them. Did mine in an hour or so. Kind of messy since you need to drain the hydraulic fluid out. My bleed screw on the control valve was frozen so I just loosened the lines to the accumulators very slightly and let the fluid drain out.

Here's one on Fastlane:

http://catalog.peachparts.com/ShopByVehicle.epc?q=1985-Mercedes--benz-300td-Suspension&yearid=1985%40%401985&makeid=63%40%40MERCEDES-BENZ%40%4063%40%40MERCEDES-BENZ%40%40X&modelid=6234%3AMBC|1518%3AED|10000135%40%40300TD&catid=241464%40%40Suspension&subcatid=2 41574@@Accumulator&mode=PA

Here is a write-up I did on for Diagnosing the SLS system
Diagnosing your SLS Sytem

Here is the info from the Factory Manual about the SLS system:
http://oregonstate.edu/~lindgrea/DIY/PDFs/32-501.pdf

The most common issues with the SLS is a leaky height valve, or bad accumulators. Sagging over night means your valve needs re-sealing, bouncy or harsh rides mean the accumulators are shot. Not rising when the rear is loaded is usually the pump.

Mine leaked down over night and had a harsh ride. I assumed I had a bad valve and bad accumulators. I replaced the accumulators first and was surprised to discover that it stopped leaking down overnight without any work to the valve.

Thanks. the PO informed that the system used to work but I noted that the hydraulic fluid tank was empty?? Leaky/cut hose or other? Not sure, but it appears that the only fluid to use is the MB stuff . . . is there a substitute to use so that I can determine the source of the leak and then flush replace with the MB product? Thanks! Great info!

I put power steering fluid in mine when the main pressure hose started leaking. Then replaced it with the Febi fluid once I had the problem repaired.

Here's a write-up on how to repair the main pressure hose if that is your problem.

http://www.peachparts.com/shopforum/diesel-discussion/192973-repairing-hydraulic-hose-sls-hydropneumatic-suspension-td.html?highlight=sls+hose

Leaky hard lines seem to be the biggest pain in the neck from what I have read on here. Most likely to occur in the rust belt I think.

If you are loosing fluid in large quantities you either have a bad hose or the pump is leaking which does one of two things depending on where it is leaking. It can either dump your SLS fluid into the motor oil, or you motor oil will fill up your SLS fluid.

As for fluid you can also use mineral oil/baby oil. But I'd only do it for a remedy for a short while. One you have the system sealed up I'd put the Febi stuff in.

Thanks! I have been reading the links provided . . since the tank has been empty for some time, should I assume that the pump is now shot? Also, car sits a little low in back, in fact, felt surprisingly good on the road - is it true that springs need to be replaced if this is the case? Seems odd that this would be as the literature states that the car is designed to ride on springs only when car is unladen in the rear? What gives?

I would be willing to bet that my pressure hose is shot, great llinks to making one up with the Gates G62 hose material . . .should be fun!

Many people here think that if the pump runs dry it will be ruined. However, there is at least one member here who drove with his pump dry for many months and once he filled it up it worked fine. So, I would not assume the pump is bad. In fact, you don't want to assume it's bad since it costs about $1200 for a new replacement.

The link is no longer working. It requires a log in, then gives
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Kerry, you are a wealth of info, thanks, loved your hose rebuilding information -hopefully I can source the Gates material. I am going to inspect pressure hose as I would not be surprised after reading so much that this may just be the culprit - are the pumps re-buildable? Thanks! James

The fine folks above have provided you with most of the info you will need. Kerry had one thing very correct; "It's almost always the accumulators"!
Your system being dry though requires a different course of action initially.
You can use hydraulic fluid from Northern Tools or from Tractor Supply to diagnose and test your system, then install the Mercedes/Febi fluid when you have it all lined out.
I imagine your high pressure hose has ruptured. All 3 of mine have done that. But you need to fill the reservoir and see what happens basically. I've also had a pump leak from in between the two halves. No hydraulic fluid in engine, no engine oil in hydraulic system. {not sure how that would even happen really} :confused:
So, get some less expensive hydraulic fluid and see what happens. Then the counter-punching can begin. Most items are super expensive new, but are usually available here on the forum or from ebay for much much much cheaper. Accumulators should be purchased new!! Only real "wear" item. And on the hydraulic line, some folks like to replace the hose themselves re-using the brass end pieces, but for not much more $$$ I have taken all of mine to a hydraulic hose repair place and is was in the $60-$65 dollar range to redo.
So, in summation, fill it, and see what happens......