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1991 500 SL; 2002 SL 500 silver arrow; 1967 Unimog 404
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34 Posts
Discussion Starter #1
1991 SL 500. ADS hydraulic fluid is full of air...looks like the head of a nice beer.
The tank is full....could the suction line be admitting air?
Anyone have this experience?
The car has sunk down very low.
 

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1991 500 SL; 2002 SL 500 silver arrow; 1967 Unimog 404
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34 Posts
Discussion Starter #3
Do you mean the “spheres” located at each wheel?
 

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1991 500 SL; 2002 SL 500 silver arrow; 1967 Unimog 404
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34 Posts
Discussion Starter #5
Hmmm. I’ve heard others say that when the sphere fails, the ride gets very stiff, and the oil resevoir drops. My suspension has dropped....and the oil level is steady.
 

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1991 500 SL; 2002 SL 500 silver arrow; 1967 Unimog 404
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34 Posts
Discussion Starter #8
I am going to check the suction line...there are two rubber sections and a steel part which runs across near the radiator.
 

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1997 SL600
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15 Posts
I know I'm a newbie here, but that means I've been doing a lot of recent learning and research, specifically on the ADS system. If you had an opening in the system as you theorize, you would end up with an external hydraulic fluid leak. Maybe a little air would get in, but any time you shut off the system, fluid would leak from that "hole".

In my opinion, you have 1 or more blown or leaking spheres. I can't tell you what the best way is to determine what axle is leaking, but I would think if the fluid is aerated, you could open a bleeder for the rear axle and see if it's foamy and repeat for the front.

Does the car return to normal height when you run it next? Does one end sag more than the other?
 

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R129 500SL ('93), W205 C200 ('14).
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134 Posts
Please bear in mind that if you bleed ADS oil from the pressure side, it usually looks "like the head of nice beer". This is because under high pressure hydraulic oil absorbs gas (like beer has done too) but the oil should become clear rather soon. Pajama01504, try provide a bit more clues...
 

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1991 500 SL; 2002 SL 500 silver arrow; 1967 Unimog 404
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34 Posts
Discussion Starter #12
Upon further investigation, I have found a rear strut leaking. In process of replacing both rears. I do not believe this would cause the rear to sag however.
I will place a pressure gauge on the banjo fitting...to check the system pressure. My repair manual says 180-190 bar is correct.
 

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1991 500 SL; 2002 SL 500 silver arrow; 1967 Unimog 404
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34 Posts
Discussion Starter #13
The rear is back on top. I pinpointed the rear lift valve as the issue. Replaced it today, and the rear lifted. The lift valve does have a pressure regulator built in, must have been stuck open.
 
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