Testing SLS operation on a 1987 300TDT (W124)?
 

I am trying to check the operation of the SLS system on my 1987 300TDT (W124.193) since the SLS valve has just been replaced.

I have found information in the FSM about checking the ride height, and the output pressure of the pump as well as info about adjusting the linkage rod but I have not found anything specific about testing the operation of the system.

I have loaded the cargo area with 400 lbs of weight to see what the effect would be. The suspension compresses about 2 inches when it is loaded, and I haven't observed any increase in height once the suspension compression occurs. Is there some minimum about the suspension must be compressed before the SLS activates? How quickly does the SLS system repond to an increased load?

I also know that the SLS pump is functioning because if the rod is disconnected to the valve and the lever on the valve is moved up and down the rear height of the vehicle changes and it moves up an down accordingly. I am just trying to test the operation of the SLS with weight in the cargo area to see if it functions properly.

Thanks in advance,

-Steve

I believe the system should respond with 2 inches of compression and bring it back level. At least my 85 does. I find the easiest way to sense the movement is sit in the driver's seat and keep my left foot on the ground. I can sense changes in the system pretty easily that way.

Thanks for the reply. Any other thoughts, descriptions, or ideas on the functionality of the SLS system?

I would have figured 400 lbs and 2" of compression would be enough for the system to respond.

-Steve

You may need to adjust the rod on the lever a bit to get it to respond to 2".

I did some testing on my 1987 300TDT just to see how the SLS responds to a load placed into the vehicle. (Prior to this testing, I also disconnected the SLS valve linkage and moved the valve lever up and down and the rear of the vehicle did move all the way up and then down.)

I "borrowed" ten 50lb sacks of sand from my local Home Depot for this test so I would have a rough idea of how much weight was being placed in the vehicle. I took measurements on the drivers side and passengers side from the ground to the opening of the wheel well. Measurements were taken with the engine off, the engine running and revved to 1500 RPM, after driving around for a couple minutes, and again after the vehicle was stopped, engine off and unloaded.

Here are the test results:



The conclusion I came to is that the SLS only compensated for the ride height by 5 mm. The total suspension compression was 35 mm in my test.

I'm not sure as to how much the SLS should compensate when under load so this may be normal?

The SLS valve can be adjusted to be more sensitive by changing the rod length, but it may also cause the system to wear faster since it may be activated by bumps as well since it is connected to the stabilizer bar in the rear. I am assuming that normally there is "dead zone" in the SLS valve so normal variations in the stabilizer bar position due to bumps, etc. don't cause the system to activate. The system will only activate (pump up the rear shocks) when a heavy load is placed in the rear as far as I can determine.

Any thoughts or ideas on how a normally functioning of the SLS operates would be appreciated.

Thanks in advance,

-Steve

When I've tested mine in the past I open the hatch and sit on the back with my feet on the ground. Then have someone start the car. I will take a second or two but you should feel the rear lifting. You can also measure from the ground to the jack hole plugs in the front and rear. Then load the car and start it and then remeasure the rear and see if it's sitting level with the front.

More SLS fun
 

Gentlemen,

I'm trying to prep a used SLS valve to go on my 87 300TDT and cannot free up the bleeding valve. Does anyone know of any tips on getting the valve to turn?

TIA

Lino

Try some penetration oil. Set the oil sit on it for a while, then tap the bleeder valve with a hammer. Then try cracking it open. I don't know about the 124 SLS but the 123 SLS systems are self-bleeding, so you don't have to do any bleeding.

Right, its self bleeding.

The 124 is self bleeding as well. I agree with Bio, penetrating oil. Put it in a vise and use both hands on the wrench or breaker bar.