Installing struts & air cells for SLS on a 91 560SEL - PeachParts Mercedes-Benz Forum

cmaxwell · #1 07-09-2006, 10:57 AM

Hey everyone,

There is an INCREDIBLE amount of great information about the SLS on various models on this board. Although, I haven't seen anything that talks about the steps for actually replacing the air cells or hydropneumatic struts, though. A lot of advice on how the system works, what to avoid, symptoms, why you should do it, etc., but I found nothing about actually installing them on my model (91 560SEL).

The person who owned my car before me replaced all of the shocks with KYB's. I know that they didn't properly convert the system to a non-hydro by replacing the springs or cross-bracing the rear shocks, so I think I'm ok in that regard (confirmed by two mechanics) as to replacing the parts with what should be there. So, I am now at the place where I want to replace the air cells and the hydrostruts, which I have. They were expensive, but I really wanted her to have the original hydropneumatic suspension.

So, basically I am asking for tips/suggestions about the installation of the air cells and replacing the struts in my 91 560SEL (115k miles).

Any information provided is much appreciated.

Thanks everyone,

Craig

P.S. On another note...the people on this board have been absolutely incredible about sharing their knowledge, and experience. I never, ever would have bought this car if this board didn't exist. Thank you everyone.

jhodg5ck · #2 07-09-2006, 11:14 AM

Hello Craig,
It really isn't hard @ all.. My biggest concern right now though is the pump.. Unless the PO looped the system back on itself (I doubt it given the quality of shock they installed) the pump will have burned itself out as it relies on the SLS fluid to keep it lubricated.

Also, is your proportioning valve still in place? That's a pricey item that is easy to remove.

All of that aside, if the lines/fixtures are still in place you will want to drop the KYB's from the bottom of the trailing arm. You'll need to remove the rear seats (two levers on the seat bottom, 8mm bolts on the seat back. The seat back lifts Up then Out. Be careful when lifting as the fabric b/w the leather and the frame like to get brittle w/ age and thus tears quite easily.

Once the seat is out you can pop out the two plastic plugs on each side (you'll need to move the factory amps out of the way assuming they are still there).

If you have the car up on stands you'll want to feed the SLS strut in from the bottom and just snug the bolt...even finger tight to start is OK. Usually the strut will collapse when you are installing it so you'll need to wiggle it back up into position..usually you can do this by sneaking your fingers b/w the leaf springs.. Worst case have someone jack up on that wheel/trailing arm to get the strut up high enough to where it pokes through the mounting hole on top..
Oh, don't forget to put your lower rubber buffer on before sticking the shock in (the thick one).
Once the top of the shock is through re-connect the SLS line, be sure you have fresh crush washers for the connection.
Everything else is pretty self explanatory once you are in there.. The system is self bleeding so no worries there. But again, my biggest fear is that the pump will no longer be functional.. I'm also worried about your high pressure line off the pump..that's a common item to fail and I wouldn’t think sitting there wiggling around empty would do it any favours.

As for the spheres, there are 3 13mm nuts and one (I think) 11mm fitting on the the sphere/feed line. Connect the feed line first, and then attach the sphere to the chassis.

Once everything is in place, re-fill the reservoir (this would be an Ideal time to take it out and give it a good clean before it goes back into service).

We're I doing this job I would attach a catch can/hose to the return line on top of the reservoir and run a Good bit of fluid through the system before doing my final fill. The MB SLS fluid is ridiculously priced, so I use John Deere Hyd. fluid.. Same base material, same viscosity just more aggressive additive package (anti corrosion/frothing etc..). You can buy this by the gallon/5 gallon bucket @ tractor supply etc, etc.

After you are done flushing, have a couple friends sit on the trunk w/ the car running, see if your system will bring the car back level. You may have to do some adjusting via the arm off the proportioning valve to get the car to sit level when unloaded. Unless you car is lowered you should be able to crawl under there and get the job done...Although I would loosen the arm before dropping the car so it adjusts easily.

That's about all I can think of @ the moment... To bad I didn't know you were in need to SLS rams, I have a very nice set sitting on the shelf!

Best of luck!
Jonathan

cmaxwell · #3 07-09-2006, 12:28 PM

Thanks jhodg5ck.,

Great information, exactly what I needed. I was worried about installing the struts. Don't know why, I just thought it might be more than I was thinking it was.

As far as the pump goes, I believe its working only because when I first got the car in LA I went to the dealer and got all kinds of fluids, and topped of the hydraulic fluid becuase the tank was about half full. It immediately came out just under the rear doors in the center of the car, which is when I realized those horrid white things (where the good stuff was supposed to be) were KYB's. I thought she was sitting low just because she needed air cells.

Incidentally, because of the fuel distributor problem I've whined about previously, I didn't drive the car home. I hauled it on an autolaoader behind a rental truck. I've had the car for over 3 months, and have only put 980 miles on her....but I'm still in love.

Again, thanks for the great information....

Craig

jhodg5ck · #4 07-09-2006, 04:36 PM

Glad to be of assitance.. I'll be curious to hear how you make out w/ all the work etc..

Best of luck!

Jonathan

cmaxwell · #5 09-16-2006, 06:44 PM

I finally had the time an patience to finish up re-installing the hydropneumatic struts and new accumulators on my car, a 91 560SEL. The PO had, for whatever reason ($$$) thought it prudent to install KYB's, while not adjusting the system to non-hydropneumatic components.

The installation of the accumulators has been well described on this board, and mine matched most accounts. I agree that the space isn't that great for re-threading the bolts, and you have to be nimble with your finger tips and very patient, but it is pretty straightforward and simple.

The struts, on the other hand, should have been as simple. Unfortunately, I'm not the brightest bulb in the chandelier, so I didn't realize that there was a second "plug" to remove to gain access to the strut behind the back seat. I spent several hours (WAYYYYYY too many), underneath the car trying to figure out how to install the strut and get the hose attached. I was taking a break from it one day and fiddling around with the dome light in the back when I realized there was another set of plugs to remove that gave you access to the top of the strut once it was installed. From there it took about another hour total. Talk about feeling stupid. I thought I had read everything possible, and researched every diagram out there before starting, but I missed that.

Other than that, the system is working perfectly. I can raise her and lower her via the control valve, and the ride is dramatically better.

With everything involved (used struts, new accumulators, new hydraulic hoses, assorted hardware, filter, fluid) I spent just over $475 total. Well worth it in my opinion. She's stock again, and she rides like a dream.

Now to the front end....

Thanks,
Craig

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