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Premium Member
1989 300SE, 1989 560 SEL and 1985 280SE Euro
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367 Posts
Discussion Starter #1
Hello all, hoping for some next level insight please. My daily driver is a 1991 560 SEL, 201k and HYPER maintained!. The main issue that I can’t seem to resolve is a less than compliant rear suspension (SLS) resulting in a disappointingly harsh ride. In the last 2 years I have tested and or replaced
SLS pump, level valve, springs and spring pads, sway links, accumulators and the rams. Actually I’ve replaced the accumulators 2x. thought was that the cortecos were stiff. Rams are OEM NEW. The system works in terms of raising lowering and not leaking. When pressing down on the rear of the car it remains too stiff. I have an 89 SEC and 560 SEL to compare to and the car is exponentially stiffer... WHY??

1- car has ASR, could that make the car inherently stiffer?
2- could a differential mount subframe bushing or another rear suspension component add to this stiffness?

Open to any and all opinions or suggestions....THANK YOU ALL
 

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Registered
1990 420 SEC
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105 Posts
Tyre dimensions have a big effect on comfort. High profile narrow ones tough they do not look as cool are the most comfortable.
 

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Premium Member
1989 300SE, 1989 560 SEL and 1985 280SE Euro
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367 Posts
Discussion Starter #4
Tyre dimensions have a big effect on comfort. High profile narrow ones tough they do not look as cool are the most comfortable.
Running standard 205/65 R15 Michelin’s
 

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Premium Member
1989 300SE, 1989 560 SEL and 1985 280SE Euro
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367 Posts
Discussion Starter #5

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Registered
1991 560sec. 1969 280SL
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971 Posts
My first 1991 560sec banged over bumps from the rear Which made the ride seem stiff. Replacing the upper shock bushings cured it.
 

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Premium Member
87 Euro500HVSEC. 88 Euro 560HVSEC. 89 Euro 560HVSEL
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4,199 Posts
Have you original SLS springs in the rear or have they been swapped out (perhaps non SLS springs in there which are stiffer)
Also have you re-set the the SLS system adjustment correctly?
With car idling in park and half a tank of fuel and no luggage in trunk the SLS adjustment is to get it to lower and then adjust so there is "ever so slight assist" from the rams (this is nuetral position) in other words when making the adjustment with the SLS lever adjusting link. The rams should not be raising the car up and nor should they be so backed off they are doing nothing.
Also those rubber bushes up the top of the shaft where locates the chassis behind the seats shoudl no be aged/compressed allowing the shaft to move up and down causing a banging noise. Can easily be fixed by placing a rubber washer under the plate that the shaft nut tightens down on to its resting position (plate only tightens down so far and stops on the ridge on the shaft)
 

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Premium Member
1989 300SE, 1989 560 SEL and 1985 280SE Euro
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367 Posts
Discussion Starter #10
Have you original SLS springs in the rear or have they been swapped out (perhaps non SLS springs in there which are stiffer)
Also have you re-set the the SLS system adjustment correctly?
With car idling in park and half a tank of fuel and no luggage in trunk the SLS adjustment is to get it to lower and then adjust so there is "ever so slight assist" from the rams (this is nuetral position) in other words when making the adjustment with the SLS lever adjusting link. The rams should not be raising the car up and nor should they be so backed off they are doing nothing.
Also those rubber bushes up the top of the shaft where locates the chassis behind the seats shoudl no be aged/compressed allowing the shaft to move up and down causing a banging noise. Can easily be fixed by placing a rubber washer under the plate that the shaft nut tightens down on to its resting position (plate only tightens down so far and stops on the ridge on the shaft)
Ok so original springs of unknown origin were replaced with KNOWN good SLS springs. Rams were sourced thru MB dealership and are mb original. Bushings on top of rams were replaced with new as well. Corteco brand accumulators sourced thru FCP Euro. I used this brand as well on the 89 SEL which rides perfectly... System was height adjusted using factory method ensuring nearly no assist under normal loads. I’ve experimented with differing ride heights and while the ride is smoother when the rear is higher than normal, it’s still way too stiff. When I open the trunk and press down on the rear there is hardly any give vs. when I do the same on the other SLS cars here.
 

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CH4S Admin , Outstanding Contributor
1985 500SEC, 1991 190E 2.6.
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39,376 Posts
Not familiar with Gen II SLS, do the current springs have any markings (under grime) and do you still have the original springs of unknown origin? Does age of fluid make a difference, or air in system?
KRH would know whether there are any markings..
The 3 dots top right will get you to advanced search, and anything issue related from the forum archive.
Otherwise, the SERVICE MANUAL & INDEX sticky on top has the Mercedes Benz USA = MBUSA hosted W126 manual. One of the discs is diesel only, .adobe flash required.
 

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1991 560SEL
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557 Posts
are you saying you recently brought new Rams from a MB dealer? they have been NLA at almost every (about 12) dealer I called earlier this year.
 

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Premium Member
1989 SEL 560
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561 Posts
My SEL 560 suffered from "dead man in trunk" syndrome for years. Like you, I replace all manner of components. One day I loosened the nipple on top of the SLS controller by the rear axle. First, I attached a clear plastic hose on top so I could see the oil coming out as I opened the valve. Use a jar to catch the fluid in at the end of the tube. A huge amount of air mixed with oil came out first. By having the clear plastic tube going up vertically before making a U-turn down you have the opportunity to see the fluid as it comes out. The U-turn configuration also gives you the ability to close the valve when all air (foamy oil) is evacuated without reintroducing air back into the system. My vehicle rides great. No more dead man in trunk when I go over a bump. It costs nothing and is easy to perform. Good luck.
 

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Premium Member
1989 300SE, 1989 560 SEL and 1985 280SE Euro
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367 Posts
Discussion Starter #14
My SEL 560 suffered from "dead man in trunk" syndrome for years. Like you, I replace all manner of components. One day I loosened the nipple on top of the SLS controller by the rear axle. First, I attached a clear plastic hose on top so I could see the oil coming out as I opened the valve. Use a jar to catch the fluid in at the end of the tube. A huge amount of air mixed with oil came out first. By having the clear plastic tube going up vertically before making a U-turn down you have the opportunity to see the fluid as it comes out. The U-turn configuration also gives you the ability to close the valve when all air (foamy oil) is evacuated without reintroducing air back into the system. My vehicle rides great. No more dead man in trunk when I go over a bump. It costs nothing and is easy to perform. Good luck.
Tom thank you. Are you referring to the height control valve and the bleed nipple on top? If so, do you recall the mm size wrench ? Also, safe to assume you bled while car was running ?
 

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Premium Member
1989 300SE, 1989 560 SEL and 1985 280SE Euro
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367 Posts
Discussion Starter #15
are you saying you recently brought new Rams from a MB dealer? they have been NLA at almost every (about 12) dealer I called earlier this year.
I bought them one at a time over the course of a year. 2 different dealers had single shocks , was lucky to get them although I doubt now that I needed them, was desperate to smooth out the ride
 

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Premium Member
87 Euro500HVSEC. 88 Euro 560HVSEC. 89 Euro 560HVSEL
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4,199 Posts
Yes i forgot to mention you must bleed the system of any air trapped in the system ( the clear tube on the nipple into a jar on the SLS valve is a good method - car idling and a helper up front topping up the fluid tank.
You can also with engine off undo the return line into the top of the fluid tank and place a clear hose over that leading to a container. Start engine and watch fluid going into the container until it is nice a clean/clear whilst topping up the fluid tank with fresh fluid as the old fluid goes into the container.
Any air trapped in the fluid in the system impacts the effectiveness of the fluid and also contaminates the fluid.
 

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Premium Member
1989 SEL 560
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561 Posts
Tom thank you. Are you referring to the height control valve and the bleed nipple on top? If so, do you recall the mm size wrench ? Also, safe to assume you bled while car was running ?
Yes, I am referring to the bleed nipple on top of the height control valve. It is the same as on the brake calipers, 11mm. Be sure to use a flare wrench so that you do not strip the hex head.
Be absolutely certain that the vehicle is off of the ground with plenty of clearance between you and the underside. The SLS may allow the vehicle to drop down and crush you if not enough room. Be careful.
 

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Premium Member
1989 SEL 560
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561 Posts
I bought them one at a time over the course of a year. 2 different dealers had single shocks , was lucky to get them although I doubt now that I needed them, was desperate to smooth out the ride
I did the same thing. One at a time yielded two different struts. Has not been a problem and now they are NLA. Keep them in reserve!
 

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Premium Member
1989 300SE, 1989 560 SEL and 1985 280SE Euro
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367 Posts
Discussion Starter #19
Yes i forgot to mention you must bleed the system of any air trapped in the system ( the clear tube on the nipple into a jar on the SLS valve is a good method - car idling and a helper up front topping up the fluid tank.
You can also with engine off undo the return line into the top of the fluid tank and place a clear hose over that leading to a container. Start engine and watch fluid going into the container until it is nice a clean/clear whilst topping up the fluid tank with fresh fluid as the old fluid goes into the container.
Any air trapped in the fluid in the system impacts the effectiveness of the fluid and also contaminates the fluid.
I always thought these systems were self bleeding? I understand the flushing but not sure how the flush procedure at the reservoir differs from the normal flow in Terms of bleeding air?
 
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