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 tried posting this on the diesel discussion forum, but I haven't gotten many responses. The SLS system is common to all W124 wagons ("T sedan"), so I am posting this here for additional visibility.

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? Has anyone observed how the SLS system works on their wagon?

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. The ride quality is normal, and the vehicle does not exhibit the bouncing/harsh ride that occurs when the accumulators fail.

Thanks in advance,

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

When I load the TE cargo area, it takes just a few minutes of driving (ie engine above 2000 rpm) for the rear to adjust upwards. Sitting at idle won't do it.

You can also use the "Search" feature above to find answers to your SLS issue. There are many posts.

Thanks for the reply about the engine rpm. I seem to recall a footnote from the FSM mentioning that the engine RPM must be above 1500 rpm.

I have searched extensively on posts regarding the SLS and there is not much about about the specific functional parameters of the system. There is no info on how to test the functionality of the system or at what point the system actually engages and pumps up. For instance is 0.5" deflection too little? Is 2" not enough? How much deflection is actually required to cause the system to self level? How long does it take?

Most posts are about a harsh ride due to bad accumulators, leaking struts, or a bad tandem pump. The posts usually deal with the replacement of the components, and not so much with the testing/checking/diagnosis of the SLS system functionality. There are also several posts on methods to remove the SLS system as well.

Thanks again for the info.

-Steve

__________________
1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

It is easy to manually test the SLS system. The lever on the control valve is connected via a linkage to the rear anti-sway bar. The bar rotates as the suspension is compressed or released, moving the level and adding or releasing pressure within the SLS system.

To test, disconnect the linkage from the lever on the control valve and move it by hand. The valve is inside of the passenger side rear wheel. A single 10mm nut is all that need be removed. Start the engine and move the lever up - the car should rise. It takes a minute or two to reach maximum height - a good 2 or 3 inches up. Looks very silly. The valve will make a rather unpleasant noise when maximum pressure is reached in the SLS system, though this causes no harm. To lower the car, move the control lever below horizontal, the car will come down. Don't crush yourself!

I had mine setup so the control level was neutral when the car was unloaded. Adding weight immediately added pressure. This seemed to give decent ride, ride height, and handling.

Note that there is a minimum pressure the valve maintains in the system, even if you leave the control lever below horizontal. The SLS normally supplies some of the suppport for the back of the car, the springs do only a part of the work.

It seems fairly common for the control linkage to slip on the rear sway bar, so it may be out of adjustment.

Good luck,

- JimY