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  #1  
Old 07-18-2002, 11:45 AM
emmy
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1991 560 sel self leveling rear end starts to sag

what checks to i need to do to determine what is causing the sag of the rear end. Are there maintenance replacement parts that i can try and replace to see whether the problem disappears?

appreciate your help...
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  #2  
Old 07-18-2002, 03:05 PM
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Join Date: Jun 2000
Location: Tucson, Arizona, USA
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Most likely, the Nitrogen accumulators need replacement. As for wear items, I would replace the bushings on top of the strut towers and the spring shims. If the sagging is different from side-to-side, I would inspect the leveling valve and the springs. Finally, if there is general slop in the rear, the subframe mount bushings could be replaced. Hope this helps, Andrew Seidel.
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  #3  
Old 07-19-2002, 01:01 AM
emmy
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thank you for your response. is the replacement of accumulators a DIY job? any site you know where i could find how tos?

thx
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  #4  
Old 07-19-2002, 01:05 AM
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Location: Tucson, Arizona, USA
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Emmy,
It is a DIY affair if you have nice metric flare wrenches and jack stands:

http://db.mercedes.cx/sec/199908/0101.html

Instructions for the other things I mentioned can be found by searching through the mbcoupes archive, as the C126 shares most components:

http://www.mercedes.cx/560SEC/archives/secq.html

Cheers, Andrew Seidel.
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75 240D
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  #5  
Old 07-20-2002, 09:27 PM
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Join Date: May 2002
Location: Mississippi
Posts: 44
Was about to change accumulators (and probably close to doing it anyway.) and had asked questions here. (By the way, I can't say how much I appreciate the folks on this board, have helped this first time MB owner very much. thanks again!)

After finding that the rear end of my 91 560SEL did not move at all I asked many questions here and finally got under the back end and was able (after some coaxing and spraying it with WD40) to get the valve to move. I ddidn't really notice anything when I did it but the car was not running. I drove it and noticed it higher than normal. I just drove the car and got in and notice the rear end very low. I started the car and drove around the block and guess what, the rear raised much to my surprise and pleasure. Now it all seems to work well.

I immediately checked on the fluid level as this is the first time the suspension had worked and noticed that the level is a little less that 1/2 in the bottle. What is the normal level? I am sure I need to change the filter, but how often should it be changed. My thoughts are to bleed the system and make sure I have fresh Hydraulic fluid in it, thoughts?

Thanks again for all the help here.

See Pics of my 560 here: http://personal.atl.bellsouth.net/lig/d/n/dnt0512/1991.htmL

:p
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http://www.bellsouthpwp.net/d/n/dnt0512/1991.htmL
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  #6  
Old 07-21-2002, 02:22 AM
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Dnthomas,
My mechanic noted a retention spring that goes around the hydraulic oil reservoir, and that it was sufficient for the oil to be above that level. The system should self-bleed, though I believe there is a bleed screw on the leveling valve. At idle, it is pumped so slowly, you can re-direct the dirty oil to a waste container as you fill with new fluid. I had the filter changed when I bought the car, but all the records show is the hydraulic fluid being changed every 15k.

Cheers, Andrew Seidel.
http://wind.prohosting.com/~sio2usa/car.jpg
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  #7  
Old 07-21-2002, 10:13 PM
emmy
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i have had the chance and go under the rear end of the car and found the two accumulators. looks like it may be an wasy job to replace.

I am however doing wverything i can to make sure that the accumilators are the cause of my problem, so i have other questions.

First, on the leveling valve that is mentioned above, is this the same as the suspension valve? i believe it is, want to make sure.
If the system is working properly, how should it behave? Here are my observations. Pls let me know your comments. With the engine running, when i put it in Reverse, i notice the rear of the car kicking up( moving upward a little bit) - is this an indication that the self-leveling is working?...Now when i put if back to Park, or put it to Neutral, then I notice the rear end moving downwards. When I put it to Drive, I notice the rear end moving downwards( yes downwards). Are these observations the result of the self leveling working womewhat, or are these just the normal movements due to the shifting changes. Is there a way to check whether or not the self leveling is working or not?

Second question. When the engine is running, I can hear some air coming from the pump. Is this normal, or is this an indication of some leakage?

thx
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  #8  
Old 07-21-2002, 11:41 PM
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Location: Tucson, Arizona, USA
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Emmy,
Yes, the leveling and suspension valve are one in the same. The leveling system works very slowly--no way you could feel it going up or down while shifting gears. I would say the squating indicates some weakness in the suspension components. There could be a leak, as mine does not make a hissing noise. To really test it, you should loosen the collar that attaches the leveling valve's arm to the rear sway bar and then move the arm up/down while the car is idling. I use a ruler and a fixed point of reference to measeure the travel. I believe the travel is only +/- a few inches. Running the engine faster than idle and having some weight in the trunk will speed the process. Using the described method, you need to be careful about fumes, lowering the car on yourself, etc.

Let us know how it turns out--the system is quite simple and durable, but repairs to it get really expensive. My struts were destroyed by the previous owner not changing the nitrogen cells soon enough--with no Nitrogen cushion, the struts were getting pounded with every bump... Cheers, Andrew Seidel.
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  #9  
Old 07-22-2002, 12:10 AM
emmy
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Andrew:
I definitely hear a hissing sound from the pump ( or so I think it is the pump). Let me describe...There are 3 cylinders connected together and covered by a plastic shroud. One cylinder is bigger than the other two. I figure the bigger cylinder is the pump. Am I correct? What are the other 2 cylinders for? I tried to feel and look which connection the hissing sound is coming from, but could not tell. Any suggestions on how to test or check this out. Would water bubble test work in this case?

thx again,
emmy
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  #10  
Old 07-22-2002, 12:40 PM
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Location: Tucson, Arizona, USA
Posts: 180
Emmy,
I wonder if you are talking about the fuel pump assembly near the rear axle. One package is the the pump, another the accumulator that regulates fuel pressure, and the other the filter (bigger one.) They should indeed hiss during healthy operation. The pump for the self-leveling system comes straight off the front of the engine, gear driven, not belt driven, quite near the hydraulic fluid reservoir. To test that pump, simply run the car in idle with the dipstick off the hydraulic fluid reservoir and you should see the fluid slowly flowing from an outlet tube that empties back into the reservoir. Please do update us on this test. Cheers, Andrew Seidel.
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85 500SEC Lorinser
83 300D Turbo
75 240D
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  #11  
Old 07-22-2002, 01:56 PM
emmy
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Andrew:
Thx for the clarification. Now I know I was referring to the Fuel pump assembly. Ok, I will update you as soon as I get the chance to work on it again.

Regards,
Emmy
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