i've searched, and still can't diagnose my SLS - PeachParts Mercedes-Benz Forum

bamba · #1 05-06-2008, 11:35 PM

I’ve spent some time searching the forum to help me diagnose and repair the SLS system on my 85 wagon. I've found some significant debate on the causes and solutions for the w123 wagon SLS system, and am having a difficult time diagnosing my problem.

I’ve found disagreement on the role of springs:

Douglas.Sherida’s rebuild:
DIY: Rebuild the self leveling suspension SLS valve on w123 300TD wagon sagging rear
But maybe springs don’t carry unloaded weight?:
sls is a sagging. 84 300td wagon

And is a jarring/rough ride a telltale sign of bad accumulators?

(post 10 in the link below)
Leveling sustem question

Or can a bad accumulator provide a bouncy ride? How can it produce both?
http://www.schumanautomotive.com/forums/showthread.php?t=2226

Here’s what I’m faced with:

Symptoms:
- A harsh ride. I can feel every bump and minor pothole.
- Sagging while parked for several hours, but rises up when motor starts.
- The kicker: I just replaced both rear half-shafts (thank you Jeremy5848 and dmorrison for superb write-ups). After replacing them, I started the car, the rear end rose, and a high-pitched squealing came from the rear end. Sure enough, it was the SLS system screaming - it kept pumping and pumping. Even before replacing the half-shafts, I had a hunch that the boots on the old ones were torn because the PO set the ride height too high. This confirmed it for me - fortunately, the new half-shafts were strong enough to prevent the SLS from rising any further (to the previously hyperextended height), and tearing the new boots (kudos to CVJ). But the SLS system was straining and screaming.

Actions:
- I put the rear end on ramps and disconnected the SLS valve linkage from the rear stabilizer bar. With the engine running, I got under the car and manually raised and lowered the SLS valve - no problem. The car rose and fell perfectly. Afraid to tear the boots on my new half-shafts, I tried to lengthen the linkage to lower the max height.

- This is where the SLS system exhibited a mind of its own. I adjusted the linkage, started the car, and nothing happened. I turned it 1/4 of a turn, fired it up, and it raised to max height with the SLS screaming at me. I moved 1/4 in the opposite direction, and nothing would happen. I played with this at least 15-20 times, and never got the same result. It was always all-out (max height) or nothing, like a runaway SLS valve.

- I got under the car and noticed that the valve would stick slightly below the “normal” position. I forced the valve past the sticky point, and the rear end would raise to max height. Only once or twice did I get the wagon to automatically raise to a reasonable height where the SLS valve properly stopped, but it could not be replicated. In the end, I decided to disengage the SLS system (removed the linkage and fully lowered the valve) until I can at least provide a temporary fix. Consequently, the wagon is currently a low-rider.

So even after researching through the forums, I am still unsure of a proper diagnosis. Is a sticky valve indicative of leaking O-rings? (the valve does NOT stick when the engine is off, presumably due to an absence of hydraulic pressure...). Is a sagging rear end indicative of leaking O-rings, a leak in hydraulic hoses, or bad springs? Is a firm, jarring ride indicative of bad springs, or just the SLS being disconnected? Come to think of it, even when the SLS was engaged before I replaced the half-shafts, the ride was still somewhat jarring, as opposed to the incredibly smooth ride that those with fully-functioning SLS have reported.

I really hope it’s a rebuild issue ($5 o-ring kits still available), and not accumulators...

Any help is appreciated!

kerry · #2 05-06-2008, 11:55 PM

I'd say the accumulators and the valve are bad. Accumulators are causing the jarring ride and a bad control valve is causing the ride height problems. Accumulators will run you around $200 for both. Valve will need to be rebuilt.

JimmyL · #3 05-07-2008, 01:34 AM

One thing you should have found with your searches: "It's always the accumulators!"

Rarely if ever is a harsh ride anything but the spheres, ie: accumulators. Also if they are compromised the leveling valve doesn't work exactly as it should.
You may still have sagging issues after you turn the wagon off and it sits for awhile if the valve is leaking internally, but when running it should be right as rain......
Also, be ready for the high pressure line to blow after you replace your accumulators. Both of my wagons did that not too long after replacing the accumulators.
If I ever get another wagon and have to replace the accumulators, and the high pressure line under the hood is original, I will have it rebuilt at the same time. {$60 bucks at hydraulic hose shop}

kerry · #4 05-07-2008, 09:11 AM

Quote:

Originally Posted by JimmyL

and the high pressure line under the hood is original, I will have it rebuilt at the same time. {$60 bucks at hydraulic hose shop}

Or do it yourself in 20 minutes with $14 in parts (new section of hose).

pizzachef · #5 05-07-2008, 09:25 AM

Quote:

Originally Posted by bamba

($5 o-ring kits still available)

Where do you get the valve rebuild kits? My mechanic was convinced that you couldn't get the kits anymore...if mine ever has trouble, I'd like to be able to rebuild it myself.

Chad300tdt · #6 05-07-2008, 09:31 AM

If you have an extra bouncy or hard ride*, you need to replace the accumulators.

*I believe this is also an indicator of the condition of your coil springs. If you have an extra bouncy ride with shot accumulators, the springs are doing their job. If you have a hard, jarring ride, the coil springs are worn.

Biodiesel300TD (Andrew) has the o-ring kits for the SLS valve.

kerry · #7 05-07-2008, 09:33 AM

Quote:

Originally Posted by pizzachef

Where do you get the valve rebuild kits? My mechanic was convinced that you couldn't get the kits anymore...if mine ever has trouble, I'd like to be able to rebuild it myself.

Forum member Douglas.Sherida was selling the remaining 0-rings he had a few months ago. Someone else may have picked up where he left off.

Chad300tdt · #8 05-07-2008, 09:34 AM

Quote:

Originally Posted by kerry

Forum member Douglas.Sherida was selling the remaining 0-rings he had a few months ago. Someone else may have picked up where he left off.

It was Biodiesel300TD.

daw_two · #9 05-07-2008, 09:35 AM

I've got 4 accumulators and one valve.

StaggerLee · #10 05-07-2008, 11:34 AM

Bamba,
One thing to check is where the linkage connects to the torsion bar (I think that's what its called). There are two small bolts that hold the linkage in place. If they come loose, it will give you symptoms similar to having bad accumulators.

Mine would be working fine, I'd put some weight in it and the back end would rise. When I'd take the weight out, it would not always return to normal and be stuck in the up (harsh ride) position.

I figured out that the linkage at the torsion bar came loose and was jamming, not allowing the car to lower.

It's an easy check and it's free too! Good Luck.

bamba · #11 05-07-2008, 12:33 PM

So correct me if I'm wrong...

With good springs and good accumulators, the ride should be smooth.

With good springs but bad accumulators, the ride should be bouncy.

With bad springs and bad accumulators, the ride is harsh/jarring.

And the SLS currently has a mind of its own because of an internally leaking SLS valve.

Do I have it right?

Is there a way to manually set the SLS height, so at least it'll ride at a normal height? Isn't there a 'normal' setting on the SLS valve, where the hole in the valve arm and the valve assembly are aligned?

StaggerLee, I'm not sure I understand your explanation - probably a matter of semantics. The linkage has two ball-ends, and connects the SLS valve to the torsion bar, which connects to the rear anti-sway bar. Right? (see Douglas.Sherida's photo, attached). So are you suggesting to make sure that "A", the linkage, is properly attached? Or is the torsion bar that you are referring to the actual link between the linkage and the anti-sway bar, which is connected with two 8mm bolts, I believe.

Bajaman · #12 05-07-2008, 12:44 PM

"Is there a way to manually set the SLS height, so at least it'll ride at a normal height? Isn't there a 'normal' setting on the SLS valve, where the hole in the valve arm and the valve assembly are aligned?"

In short no. The sls valve operates by changing the amount of fluid in the struts/accumulators. It does this in response to the ride height. If you leave the valve in the fill position, you will get the high pressure noise and ride height that you have observed. leave it in the off position, and you experience the sagging. I really think that you should start by replacing the accumulators, and alleviate your harsh ride. After that, you will be better able to diagnose the valve operation. Or, just rebuild the valve while you've got it apart for piece of mind, either way, I think a set of accumulators is in your future.