[W126 Coupe] Help me narrow down self leveling problem

Sat Jun 3 11:48:41 EDT 2006

I can diagnose the "bad spheres" problem, been there - done that several
times, but I'm not familiar with one that's too soft. There are a couple of
things I'd check though.

- Make sure the system is full of hydraulic fluid and the fluid that's being
returned into the reservoir is free of bubbles.

- test the valve (engine running, get under the car and move the arm, verify
the car moves)

- verify the valve arm is tight on the sway bar (8mm nuts on the u-bolt).

The shock action in the back is accomplished by the hydraulic fluid moving
into and out of the accumulators. The amount of resistance is the
combination of the hydraulic fluid viscosity and the ID of the hydraulic
lines to the rams (shock looking things inside the springs). 

About the only thing you can do if there is too much free movement in the
back is to replace the hydraulic fluid with new to make sure you have the
correct viscosity fluid in the system. With the engine off, remove the metal
hydraulic fluid return line into the reservoir in the engine compartment and
direct it into an empty bottle (2L soda bottle works great). Start the
engine and the pump will drain the system and pump it into the bottle. When
the reservoir is empty, put new fluid in there and when clear fluid is
coming out of the return line, shut off the engine and put the return line
back onto the reservoir. You'll still have some "old" fluid in the rams and
accumulators but that will eventually mix with the new fluid as you drive
and the rear suspension is moved. 

Later,

Mike R.

(702) 494-8056

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From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com]
On Behalf Of Matt Jurcich
Sent: Saturday, June 03, 2006 8:10 AM
To: Mercedes Coupes Mailing Lists
Subject: Re: [W126 Coupe] Help me narrow down self leveling problem

Hi Mike,

Thanks for your detailed response.  As the rear end is not rock hard, I
think the core of my question is should I replace the spheres first or try
to diagnose the valve first (or some other part back there)?  I didn't see
much about this particular situation in the archives.  

Any suggestions on diagnosing the valve?

Thanks again!

-m

On 6/2/06, Mike R. <mramay at att.biz> wrote:

This hydraulic system is under high pressure, so, with the engine off,
you'll crack a fitting loose and let it depressurize. There's a bleed valve
on the control valve if you want to use that. About a half quart of
hydraulic fluid will exhale. If the bladder in the accumulator is intact, a
Phillips screwdriver will go about 2 - 3" into the opening for the large
fitting. If it goes all the way in (>5"), the bladder is shot. You can look
in there with a mirror to see if the metal/plastic centerpiece for the
bladder is pressed up against the hole. If all that is there is a black
hole, it's bad.

You don't seem to have that problem as a blown bladder will allow the
accumulator to fill with hydraulic fluid and once one goes bad it tends to
overload the other one (they're in parallel) and the second one will fail
shortly afterwards. With both accumulator bladders blown, the rear
suspension has no more movement capability - it is a solid rear suspension.
Jumping on the bumper moves the back of the car only as much as the tire
sidewall flex will allow. Rides REALLY bad then!!

The only way I could feel/see movement of the rear of the car, with the
engine near an idle speed, is to lay under it with my shoulder between the
bottom of the trunk and the ground, then manipulate the level control valve
on the sway bar. It moved SO SLOW that I could feel it change the pressure
on my shoulder long before I could see it move. Like Jonathan said, it's
SLOW. 

All that said, I'd check tire pressures first, they should be around 35psi
in the rear and about 32 psi in the fronts. Stock 15" rims have tires with
enough sidewall that under-inflation will give you lots of movement back
there.

Later,

Mike R.

(702) 494-8056

  _____  

From: mbcoupes-bounces at mbcoupes.com [mailto:
<mailto:mbcoupes-bounces at mbcoupes.com>  mbcoupes-bounces at mbcoupes.com] On
Behalf Of Matt Jurcich
Sent: Friday, June 02, 2006 3:56 PM
To: Mercedes Coupes Mailing Lists
Subject: Re: [W126 Coupe] Help me narrow down self leveling problem

Should I be seeing any movement when working the valve lever if the
accumulators are shot?  I have located them and visually seemed fine,
although I understand the leak for these is between the two interior
sections of the unit.  

Some have recommended removing the oil line from it, and sticking a
screwdriver in and seeing if it only goes a couple inches in to feel for the
membrane.  Is that reliable or should I just change them?  

Thanks!!

-m

On 6/2/06, mavris2 at comcast.net <mavris2 at comcast.net> wrote: 

Matt,

Check your Accumulator's, if they are leaking then that is your problem.
They are located under the rear of the car and are oblong and black in
color. One on each side.  If one is leaking you need to replace both of
them.   It should be a firm but yet not to soft of a ride if that makes
sense. If the back end is bobbing a lot then most likely the accumulators
are bad.  Typically they leak when they are bad indicating that they need to
be replaced.      

Jason 

----- Original Message ----- 

From: Matt <mailto:invisik at gmail.com>  Jurcich 

To: mbcoupes at mbcoupes.com 

Sent: Friday, June 02, 2006 5:08 PM 

Subject: [W126 Coupe] Help me narrow down self leveling problem

Hi all,

I've been reading many many threads on the rear self leveling suspension.
Lots of great info out there.  My car, however, doesn't seem to fit the
typical symptoms.

Car is level and the ride is too soft.  I have fluid in the resivoir.  If I
load up the trunk with the car on, rear does not react at all.  I got under
the rear end, found the valve and with a wrench moved the level up and down
and didn't get any reaction either.  

How long does one need to hold the valve lever in the up or down position to
expect movement to start?  I only held it there for a few seconds.

I don't want to just start throwing parts at it--way too expensive for that!
I will check the filter in the resivoir tonight.  The leveling has not
worked since I purchased the car a couple of months ago.  The rest of the
car is in great shape, everything works on it (Even cruise control!)

Thanks for any suggestions on what to look at next.  89 560 SEC

-m

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