Excellent work! Congratulations job well done.

 

Fyi, i have bought all accumulators, dampener and one remanufactured strut. Hoping to put them in next month. Now i will be checking control arm and bushings too. Thanks for updating results of your project. I will post results also

 

It's not that bad a job! I have a 2004, though, so I'm not sure how much it changed to your year of 2007. If the car lived in New Mexico, where I see you are located, all nuts and bolts should come off easily. Mine lived in Southern California its whole life, so there isn't a spot of rust on anything. It's quite amazing compared to cars from the North East where I live!

Now that I have done it once, I honestly think I could swap a strut in about 30 minutes after the car is on the jack stands! I solved a lot of small roadblocks, though, so if you have any questions, just reach out. Good luck!

 

OK, I finally did it. I replaced front and rear accumulator and replaced the front right strut because it was seeping oil. I had the alignment checked by a local shop. It was reported within spec. I ran the rodeo and did the height up and down a bunch of times to clear air and I scanned for codes at this point there are none initially I did get one SBS c25d8 code, but it has not returned. Unfortunately, the car still rides extremely stiff. I can’t distinguish that it’s stiff on one particular corner. It seems to be from all corners. I hope somebody has some insight on what I should look at next. I’m thinking maybe the return solenoid on the valve blocks is stuck? I really have no idea. Please help

 

You should be able to activate the ABC (put it in gear with the park break engaged) and walk around to each corner and using your body weight get some vertical movement at each corner. I would think they should feel similar.

If any strut is locked, I would suspect a bad blocking valve in the ABC valve block. Seems very unlikely it's a seized strut, but I guess that's possible. The blocking valves block fluid from leaving the struts when the car is parked. They use solenoids to open them. Bad solenoid or no electrical signal and the valve stays closed.

Keep us informed.

Also, I've had great luck with Arnott strut rebuilds. I think I paid about $800 for a front.

 

OK, back on the SL 55. When I push on four corners with car running parking brake engaged there’s very little movement on the front left and right but there is movement. The rear left and right similarly are very stiff. No discernible movement. So I’m thinking my next step is to replace the rear valve block. In reading different forums I’m confused on whether to buy a genuine Mercedes replacement or a remanufactured valve block. My issues is obviously not with the O-rings, but one of the return solenoids.

 

I'll assume you did this test with the car in gear to engage the ABC........right? And that the stiff rear end is consistent with your ride issues?
In terms of a "rebuild".......... nobody can properly test the valves, all they do is clean it up and put new o'rings in. And the most sensitive areas are the leakage at the blocking valves (these aren't really return valves) because even minor leakage causes the dreaded corner droop when the car is parked. I'd stick with OEM. However, that said, a new one is about $1500, and if you don't mind taking a chance with your labor, buy a used one on eBay for $1-200, but make sure the seller takes returns. Also note that there's an older one where the 4 solenoids are separate, and a newer one there the solenoids are integrated in pairs. The newer it is the better in my mind just because it's newer.

This is not a tough job, but If you haven't done it before, recognize that the hoses connect to the valve block with quick disconnects, however there is a special tool to decouple them. I've done it several times using needle nose pliers and similar fork like jury rigs, but it can be a pain and it's kind of hard on the QD's. I don't know where to buy that tool......but if you can find it, it's worth getting I think. Also be sure to bleed system pressure at each of the rear shocks. I'd jack up the whole rear end to avoid expelling all the fluid from the right rear strut that will otherwise collapse when the hoses or bleeders are opened.

Let us know how it goes and if you find that special too, drop us a picture and the source.

 

OK, I took the car to a friend’s auto shop and we again performed the test, with engine running and tranny in drive except this time he actually sat on the trunk then the front corners. There was similar movement at all four corners . none of them were locked stiff so I feel like I’m back to square one, except that I’ve replaced the accumulators , one front right strut which was leaking and then two front accelerometer, a process of elimination. None of the parts were super expensive and I did the labor myself. Assessing the problem while driving I sometimes think that it’s the front corners that are stiff but it’s difficult to tell and sometimes I think it’s all four corners. The stiffness is most evident going over bumps road imperfections and such, hard turns one direction to the other feel normal if the road is smooth. in my inexperienced mind I think the only remaining contributing parts are the valve blocks. If that is true, then I don’t mind replacing them. Maybe its a stretch but i once thought it could be a bad motor or tranny mount. Not sure how those would manifest. I wonder if i am on the right track with valve blocks???

 

Well, I think that eliminates the valve blocks/suspension as the problem. I'd be reluctant to mess with an ABC that's well maintained and working correctly, no codes.
Motor mounts are a good culprit............trans mount is cheap and easy to swap. If you don't know the history of the motor mounts..........well worth replacing. They aren't that expensive, but they are a bit of a pain to R&R. If I recall, there's a special (but cheap) special wrench required. However, I'd say that the MM's don't affect handling at all and manifest as rumbling thru the body and vibration/noise. So, I am perplexed at this point given that you apparently are trying to address a chassis like issue. Is that correct?
Let us know.

 

I was hoping I could just replace the valve blocks and be done with it, but that’s obviously not the case. I will stop and think about other variables. I guess I can further define stiff ride by saying that I feel all the imperfections in the road. Pretty consistent sensation but i get confused because sometimes it feels rougher than others. It’s almost like I’m driving on solid concrete tires . if the road is smooth the car drives fine if there’s a 1.5 inch asphalt step then the whole car feels it , not just through the steering wheel. there are no metal to metal bangs. There is no ongoing vibration beyond initial bump. Sharp aggressive turns the car stays level and if the road is smooth feels fine. during this period about a year ago, concurrent with stiffness, the vario roof bagan rattling and making noise. the suspension up and down height adjustment work fine. about a year and a half ago I took a long sweeping turn one I’ve done many times before at over 120 miles an hour and it did not feel like it was tracking correctly. No clunks just a little swervy. Maybe unrelated. No fault codes during any of this

I would really like to solve the problem. I like the car. I dont drive it often but love it when i do. I certainly dont want to sell it with problem known to me

a real conundrum


I believe a strut either works or it doesnt. My struts appear to work?

i cant imagine that a valve block could have a valve that only partially opens, or stuck partially open. My car is 2007 abc2. The car rides level and at consistent heights

i wonder if motor tranny mount can be inspected in place. I have hard time thinking these mounts are causing the problem but i bet they are stock, 20 yrs old.

This car used to drive smooth

 

To me this sounds like bad struts. My Bentley Brooklands also had a hybrid hydraulic suspension system with accumulators as well as electronically adjustable shocks. When the car sensed (don't ask me how) the shocks were "worn out" it would lock them into their most firm setting. Which actually made the car ride a lot like it did when the accumulators needed replacing. Both working properly together gave the car it's tradmark ":firm but supple" ride which is not unlike an ABC Benz car. But if either the spheres had lost pressure or the shocks internal damping was questionable, a rock hard ride was the result.

If you've swapped the spheres and you know they are good, I would look at shocks/struts next. Are OEM units even available ?

The high speed wander/weave sounds like tires. I only run Pilot Sports on the SL and it tracks like a freight train. If you have different tires front and rear, that's a textbook cause for the behavior you have now.

 

F1: I'd say the ABC seems to be working fine. If the car raises and drops using the console button, and it doesn't droop when parked, then I think the valve blocks are fine. If the accumulators were bad, you'd be getting an ABC warning in the dash. Like you, I don't think the struts have any failure modes that make the stiff. I can't speak to triple downs thoughts/experiences but the Bently uses electronic damping control, and the SL doesn't. The SL has fixed damping and the ABC just uses pressure in the struts to keep the car level. His point on tires however is valid as regards stability in turns, but it wouldn't explain the variable harshness that you feel. I think you are on to something with the motor mounts. After 20 years, I'd darned near guarantee they are shot. The Trans mount holds up much better as it's just rubber, whereas the motor mounts are fluid filled and once they leak........they just die all at once. And, if the engine mass is flopping around, that could result is the instability you experience in turns. When they fail, you don't get any metal on metal banging in my experience. In terms on inspection, you might be able to get a peak at one or both, but all you might be able to see would be some wetness........but that's far from certain as if they leaked out, and it's been a while age, they'll likely look dry. I'd just replace them. And recall that I mentioned a special wrench (cheap) that's necessary to get at a nut/bolt on one (Right side I think). You can easily eyeball the trans mount, and it looks like the rubber is more or less intact, you can skip it.........I'd bet it's fine. Let us know.

 

Thanks for the feedback. It helps me a lot. Tames my imagination. I’ve run the four corners up and down with a scanner and also had data while driving and all the pressure and height voltages are similar. I called arnott and they said if there’s no fault code and they go up and down the struts are fine. Also cornering on smooth pavement suspension seems to perform as well as it ever has. I’m not getting any corner sagging. So i will put in motor mounts and we shall see. I ordered them from Rockauto and I got the more expensive ones . (DEA/marmon $244) I don’t know how quickly I’ll get these installed but I’ll update once I do.

 

You sure about that? I've had this discussion with my indy about ABC before. He any I both believe that there is adjustable damping in the strut itself and there is definitely an electrical connector on my 2009 near the top of the shock tower. AI sez:

"

• Active Adaptation: The factory ABC struts feature integrated control valves managed by a dedicated suspension Electronic Control Unit (ECU). Sensors analyze the vehicle's body movement, pitch, and yaw, instantly firming up the struts during aggressive cornering and softening them during highway cruising."

I still say if you have a rock hard ride, the shock is the cause. Now whether that is due to a physical malfunction in the strut or an electrical issue in the ABC ECU, that is certainly up for debate. Something is keeping that valve closed and limiting fluid movement in the damping part of the shock.

 

I think we are going to find out. One way or another. Right now its reasonable for me to replace the motor/tranny mounts. They are old anyways. I have already replaced one strut because it was seeping hydraulic oil but still functional. There was no electrical connection on the strut, only hydraulic. There was/is a connection at the accelerometer near top of strut but separate from strut. I think there is a pressure and height sensor somewhere but i dont think they are in the strut either. This is a 2007 sl55 abc2. Maybe 2009 is newer pneumatic. We will see what condition mounts are in - they are 20 yrs old, the car is not driven mildly.

 

2009 SL550 is ABC2 as well. You're helping us all understand these better as it's only a matter of time before we are all in your shoes.

Keep up the great work !

 

Great.
And here an Amazon link to the wrench that you will absolutely need for the job. Otherwise I think you'd have to pull the engine part way out.
Let us know if this does it for you.

 

OP what tires are you using and at what pressures?

 

I think the following is correct regarding the struts and the function of the electrical connector on top of each. Note that for example the front struts on my '03 SL 55 AMG have p/n 230-320-44-13, whereas a front strut on a '09 SL 63 AMG has p/n 230-320-39-38. So, there's some differences.On the early R230 ABC struts (especially pre-facelift):

• It is associated with the internal plunger/travel sensor (“plungerweg sensor” in Mercedes docs)
• Also provides diagnostic feedback
• Mercedes documentation notes that later facelift cars after ~2006 eliminated the plunger sensor in the strut and instead inferred information from pressure sensors. Used by the ABC ECU for additional hydraulic/strut movement monitoring (same purpose, different type of measurement). Both use a lever sensor at the lower control arms to sense ride height, and the ABC valve blocks adapt the flow to at each strut to maintain a level posture. None of this affects the damping, which I believe is fixed hydraulically inside the strut, although damping can be tuned for the strut positions is shocks, I don't know if that's the case with these but given the sophistication of the design I bet it a variably damped shock. Of course, all shock damp more the faster they are moved, so that's the inherent variable damping.
  
  Here’s a simplified layout of the suspension:
  
  
  Code:

          BODY / STRUT TOWER
                |
                |   Electrical connector
                |    for internal ABC
                |    plunger sensor
             [ABC STRUT]
                |
                |
        -------------------
        LOWER CONTROL ARM
               /
              /
     Lever linkage
            /
   [Ride Height Sensor]
        mounted to chassis
  
  F1: did you say you have a '09? and how may miles are on it? 
  And do let us know is the motor/trans mounts do the trick. I can't wait!  
  

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