SLS Valve Mystery - PeachParts Mercedes-Benz Forum

warmblood58 · #1 10-25-2009, 06:04 PM

Here is a weird one - just replaced bad accumulators on my '84 300 td wagon and found a used SLS valve as my valve would not seal. Car held ride height for an entire night without the adjustment rod (which is new) connected. Yesterday, I made the adjustments to the rod to allow for proper ride height and noticed that after shutting off engine, car would not maintain ride height and sink from 13 inches to below 12 in a matter of minutes??? Today, I disconnected adjustment rod and set lever to hold ride height at 13 inches and car holds height just fine without engine running. My belief is that when the rod is connected, there is some pressure on the lever rod which allows system to bleed off somehow - no visible external leaks of any kind as all connections are tight, new z links were just installed -has anyone else ever experienced this problem? Also, has anyone ever found a source for a new sls valve that is priced reasonably? I was thinking that I could order Doug's o-ring kit and reseal but before I do this, I thought that I would consult the forum pros -thanks!

kerry · #2 10-25-2009, 06:24 PM

My experience with SLS valves which bleed down is that if the valve is in a slightly different position from 'normal' it won't bleed down. I assume something is worn in the 'normal' position. When I replaced my accumulators, the SLS stopped dropping overnight for about 9 months. I've noticed that recently it is sometimes dropping down.
Not sure what a 'dropping valve' means when the car is running. Does it mean that the pump is working more than it would be if the valve were holding? Or, is the pump always producing x amount of pressure whether it is going into the accumulators or not?

Biodiesel300TD · #3 10-25-2009, 07:20 PM

Typically if the rear is changing height without loading or unloading the rear the valve is leaking. This holds wether the engine is running or not. With the engine running the rear can raise and lift without loading, and without the engine running the rear usually sags.
If the pump isn't working the rear won't lift when loaded.

I have the SLS Valve O-ring kits. If you need one or two kits let me know.

warmblood58 · #4 10-25-2009, 08:16 PM

Quote:

Originally Posted by Biodiesel300TD

Typically if the rear is changing height without loading or unloading the rear the valve is leaking. This holds wether the engine is running or not. With the engine running the rear can raise and lift without loading, and without the engine running the rear usually sags.
If the pump isn't working the rear won't lift when loaded.

I have the SLS Valve O-ring kits. If you need one or two kits let me know.

thanks, but reread my post - car holds pressure and ride level when adjustment arm is not connected to torsion bar mount -it also holds same level when engine is running -

Biodiesel300TD · #5 10-25-2009, 08:49 PM

With the adjustment arm connected is the lever arm on the valve parallel with the ground? With the car running the lever arm should be parallel. It sounds like maybe the adjustment arm is too short and so when you shut the car off the valve thinks you've unloaded the car and it opens the valve to allow fluid out to lower the car.

The way the valve works is when the lever arm is parallel to the ground the car should be at it's normal ride height. When you load the car the rear end of the lever arm should go down which tells the valve that more pressure is needed and it pump fluid through the system to lift the rear until the arm is level again. When you unload the car the rear of the arm will go above level and then the valve releases pressure until the lever are is level again.

kerry · #6 10-25-2009, 08:53 PM

I can hear my system releasing pressure from the system if more than 3 people get out of the car when I stop.

warmblood58 · #7 10-25-2009, 09:09 PM

Quote:

Originally Posted by Biodiesel300TD

With the adjustment arm connected is the lever arm on the valve parallel with the ground? With the car running the lever arm should be parallel. It sounds like maybe the adjustment arm is too short and so when you shut the car off the valve thinks you've unloaded the car and it opens the valve to allow fluid out to lower the car.

The way the valve works is when the lever arm is parallel to the ground the car should be at it's normal ride height. When you load the car the rear end of the lever arm should go down which tells the valve that more pressure is needed and it pump fluid through the system to lift the rear until the arm is level again. When you unload the car the rear of the arm will go above level and then the valve releases pressure until the lever are is level again.

I will readjust adj arm using the factory orienting hole in valve body and see if anything changes -right now, lever is pointed downward slightly as I adjusted lever first to give me a ride height of 12.75ish and then adjusted arm to maintain that adjustment

nhdoc · #8 10-26-2009, 08:25 AM

The adjustment arm will alter ride height but the valve should always find "center" itself. In other words when the car is loaded the arm pulls up and opens the valve to "pump up the rear" until the arm centers. Similarly, when the car is unloaded the arm swings down and fluid is drained until the arm centers. You don't set the center, it sets itself. If you shorten the arm you raise the ride height and if you lengthen it you lower it. That's the car's "set point" which it will always try to maintain.

If the car drops after you shut it down then the valve (or something else in the system) is leaking, period. If you are not losing fluid anywhere then it is the control valve which is allowing the fluid to bleed off.

warmblood58 · #9 10-26-2009, 12:59 PM

Quote:

Originally Posted by nhdoc

The adjustment arm will alter ride height but the valve should always find "center" itself. In other words when the car is loaded the arm pulls up and opens the valve to "pump up the rear" until the arm centers. Similarly, when the car is unloaded the arm swings down and fluid is drained until the arm centers. You don't set the center, it sets itself. If you shorten the arm you raise the ride height and if you lengthen it you lower it. That's the car's "set point" which it will always try to maintain.

If the car drops after you shut it down then the valve (or something else in the system) is leaking, period. If you are not losing fluid anywhere then it is the control valve which is allowing the fluid to bleed off.

Here is what I do not understand, car drops only when I detach adjustment rod (with engine off) With engine running and rod attached, car maintains height that I adjusted the rod to and should when I turn engine off as there is no load in car - car will hold height perfectly with engine off with adjustment rod disconnected from valve lever . . . . weird!

Biodiesel300TD · #10 10-26-2009, 02:25 PM

You are confusing me. So the rear only drops when the adjument rod is disconnected, and everything works fine when the rod is attached. If so I don't understand what you are worried about.

warmblood58 · #11 10-26-2009, 02:36 PM

Quote:

Originally Posted by Biodiesel300TD

You are confusing me. So the rear only drops when the adjument rod is disconnected, and everything works fine when the rod is attached. If so I don't understand what you are worried about.

No, read again please - if i do not attach adjustment arm to valve lever, car will maintain ride height with engine off (it is my understanding that ride height is maintained on a working system when engine is off -car should not drop) when I attach adjustment rod to valve lever and start car, ride is maintained -when I shut off engine with adjustment rod attached to valve lever -car will slowly drop. My understanding is that the adjustment rod allows you to set ride height and car will maintain that height when engine is off - right now, I have ride height set to 13 inches measured from center of wheel star to fender lip. I am wondering if in fact that any pressure on the valve shaft (as in the adjustment rod being connected) is putting some kind of torsional pressure on shaft/orings and allowing pressure to bleed off somehow . . . does this make sense Doug? Thanks!

StaggerLee · #12 10-26-2009, 03:17 PM

I'm not positive but I thought the condition of the rear springs determined the "empty" and "off" ride height, not the SLS adjustment. Ride height with the engine running is another story.

warmblood58 · #13 10-26-2009, 03:32 PM

Quote:

Originally Posted by StaggerLee

I'm not positive but I thought the condition of the rear springs determined the "empty" and "off" ride height, not the SLS adjustment. Ride height with the engine running is another story.

hmmm . . . many people have stated that the sls system is supposed to maintain ride height (as set) with the engine off which is why many people complain about their cars rear ends dropping over night -

Biodiesel300TD · #14 10-26-2009, 04:03 PM

The springs are supposed to maintain unloaded ride height, which also happens to be where the lever arm is level with the ground. But when the springs get tired they cause the rear to sag, which causes/forces the SLS system to maintain the unloaded ride height, keeping the lever arm in the level position. In a system with worn springs and no leaks the SLS system will maintain the unloaded ride height all the time. But if you have a leak in the system the rear will sag down until the springs are holding the height. Then when the car is started up the system pressurizes again and the rear lifts up.
With that said you can change the ride height using the SLS system, but you are causing the SLS to hold the unloaded height not the springs.

If your rear is settling with the rod attached, dispite what it does when it's not attached, the valve is leaking. It can leak internally which allows the SLS fluid to flow when it's not supposed to.

kerry · #15 10-26-2009, 04:39 PM

There's have been lots of debates here about whether the hydraulic cylinders are designed to carry some load under all conditions. I believe the last post I read on this topic offered some kind of definitive statement on the issue, indicating that even with the car unloaded the SLS rams are intended to carry part of the load.