self-levelling height adjustment for w123 - PeachParts Mercedes-Benz Forum

#1 01-24-2004, 03:21 PM

How do I adjust rear ride height and what tools are necessary?

While wer're on it, how exactly does the sls work?

You've got the hydraulic fluid operating a level controller attached to the sway bar but then you also have hydraulic shocks...does the hydraulic fluid supply both the level controller and the shocks and to what effect?

Paulwho · #2 01-24-2004, 07:57 PM

shawnster,

This info pertains to the rear hydraulic suspension not the 4 corner hydraulic suspensions (rare).
1) The rear springs support the vehicle when unladen
2) The sls is only utilized when weight is added to the wagon.
3) Raising the rear of the vehicle with the control linkage
will shorten the life of the accumulators.
4) If the rear is low, springs and or bump pads are needed.
5) When the control rod is properly adjusted a pin can be
inserted thru the actuator arm into the control valve.

#3 01-25-2004, 11:12 AM

I had new shock mounts/bushings replaced about a week ago. Mechanic said that he "flushed and refilled" the hydraulic fluid but that I'd have to handle re-adjusting ride height.

It's quite a bit lower than previous to the work.

Is it possible that it requires bleeding air out using the bleed screw?

Would I do the following:
loosen the screws on the turnbuckle on the torsion bar, then
insert a pin or small screwdriver through the lever and into the hole on the side of the controller body, then
tighten the screws on the turnbuckle.

or do I shorten or lengthen the lever?
how do I pop off the lever on either side?

#4 01-25-2004, 11:47 AM

chicken vs. egg routine here:
if i would remove the controller lever and never do another thing with it, the car, while unloaded, should be at "normal" height which is maintained by the shocks and springs.

its NOT that the level controller applies force to the torsion bar to change or maintain ride height.

it IS the additional weight of a load pushing down on the torsion bar which activates the lever controller to pump more fluid into the shocks and therefore adjusts for load.

Am I right? (please tell me I'm right)

Paulwho · #5 01-25-2004, 08:55 PM

shawnster,
Now you understand

cgoodwin · #6 01-26-2004, 12:16 PM

OK, here's the deal. Both very soft and very hard rides can result from failed accumlators, the suspension should be the finest in the world, no holds barred, it should be firm but smoothe, absorb bumps silently and smoothly, keep a level vehicle regardless of weight and you should be able to run over a brick with just one rear wheel, going around a corner and still cut a diamond in the back seat... OK a bit extreme but not far off.

First you need to know how the system works. You have a belt driven hydralic pump, the pressurized fluid passes through a line to the leveling valve. This valve has an actuating lever attached via an adjustable rod to the sway bar. When the rear of the car is depressed, the valve opens and forces fluid through the accumulators and into the "Shocks" which are actually hydralic rams, these raise the car until the lever is again level and valve closes. The accumulators simply absorb the shocks with compressed gas. Now look at each seperate system.

Leveling. Since the "shocks" are simply rams which raise the vehicle, and fluids do not compress this system is very hard without the accumulators. To check the system, shut the vehicle off, measure from the ground to the wheel arch and write it down. Now place weight in the rear, try opening the trunk and having two people sit on the rear. Measure the didtance again, it should be less with the weight. Now with the weight still in place start the engine and run it at about 1500 rpm for a minute or two...The rear should raise to the original level, if it does not, there is a problem - regardless of the accumulators.

Next raise the vehicle and look at the valve, it has a lever with an adjustable rod connected to it, the other end of the rod connects to an arm attached to the sway bar with a clamp (this clamp can slip lowering the vehicle). Disconnect the rod from the lever on the valve and rotate the lever upward to about 45 degrees. Lower the vehicle to the ground and again run the engine at 1500rpm, as soon as you notice the rear begin to rise, shut the engine down (as not to hyper extend the leveling rams) - OK it it went up then the valve, pump and rams all work. If it did not go up then you need to go into the system more carefully - let me know and I can explain, but since this is rarely the issue I will skip ahead.

The rod can be adjusted by turning the center and shortneing or lengthening the rod. Each two turns shorter raises the vehicle about 1" each two turns longer lowers the vehicle about 1". Keep at it until you get it level and there you go.

Shock absorbtion. Since the leveling system is hydralic and fluids do not compress, if you hit a bump, it will feel like the rear is solid. So the fluid runs into a sphere which is devided by a membrane, on the other side of the membrane is gas presurized to about 1700psi, when the vehicle hits a bump the fluid is forced from the ram and down the line into the oil filled side of the accumulator and from there to the valve, which should be shut because the vehicle is level. The only place which can give is the gas filled side of the accumulator, which it does and just as rapidly the gas expands and forced the ram back to its original position - Just like in a gas filled shock absorber. Get it? the "shock" is actually just a ram which raises or lowers the rear end, the accumulator is actually the "shock"!

If you have a very hard rear end when driving, OR if the rear seems to "wollow" or be very soft on the road then most likely you have bad accumulators but don't take my word for it, test them. The simplest way I know is to unscrew the hose going from the accumulator to the "shock" - BE VERY CAREFUL - the fluid is under a lot of pressure and will spray abut a coffee cup of oil everywhere. With the line off slide a small punch into the end of the accumulator, it should go no more than about 1/2 inch in, if it goes 3 to 4 inches in, the diaphram is gone and the accumulator is worthless and must be replaced.

Do not simply gut the hydramatic system and replace it with springs and shocks, you would be replaceing a remarkable system with a very basic one. Once working you can load the car down and have a level ride, you have a system which works better than just about anything on the road and you have no shocks to go bad.

If you need more info let me know and I will help as much as I can. I have a 1989 560 SEL, looks and runs like new with just under 200k...With hydramatic suspension.

Chris

Dee8go · #7 03-23-2009, 08:34 AM

Quote:

Originally Posted by cgoodwin

OK, here's the deal. Both very soft and very hard rides can result from failed accumlators, the suspension should be the finest in the world, no holds barred, it should be firm but smoothe, absorb bumps silently and smoothly, keep a level vehicle regardless of weight and you should be able to run over a brick with just one rear wheel, going around a corner and still cut a diamond in the back seat... OK a bit extreme but not far off.

First you need to know how the system works. You have a belt driven hydralic pump, the pressurized fluid passes through a line to the leveling valve. This valve has an actuating lever attached via an adjustable rod to the sway bar. When the rear of the car is depressed, the valve opens and forces fluid through the accumulators and into the "Shocks" which are actually hydralic rams, these raise the car until the lever is again level and valve closes. The accumulators simply absorb the shocks with compressed gas. Now look at each seperate system.

Leveling. Since the "shocks" are simply rams which raise the vehicle, and fluids do not compress this system is very hard without the accumulators. To check the system, shut the vehicle off, measure from the ground to the wheel arch and write it down. Now place weight in the rear, try opening the trunk and having two people sit on the rear. Measure the didtance again, it should be less with the weight. Now with the weight still in place start the engine and run it at about 1500 rpm for a minute or two...The rear should raise to the original level, if it does not, there is a problem - regardless of the accumulators.

Next raise the vehicle and look at the valve, it has a lever with an adjustable rod connected to it, the other end of the rod connects to an arm attached to the sway bar with a clamp (this clamp can slip lowering the vehicle). Disconnect the rod from the lever on the valve and rotate the lever upward to about 45 degrees. Lower the vehicle to the ground and again run the engine at 1500rpm, as soon as you notice the rear begin to rise, shut the engine down (as not to hyper extend the leveling rams) - OK it it went up then the valve, pump and rams all work. If it did not go up then you need to go into the system more carefully - let me know and I can explain, but since this is rarely the issue I will skip ahead.

The rod can be adjusted by turning the center and shortneing or lengthening the rod. Each two turns shorter raises the vehicle about 1" each two turns longer lowers the vehicle about 1". Keep at it until you get it level and there you go.

Shock absorbtion. Since the leveling system is hydralic and fluids do not compress, if you hit a bump, it will feel like the rear is solid. So the fluid runs into a sphere which is devided by a membrane, on the other side of the membrane is gas presurized to about 1700psi, when the vehicle hits a bump the fluid is forced from the ram and down the line into the oil filled side of the accumulator and from there to the valve, which should be shut because the vehicle is level. The only place which can give is the gas filled side of the accumulator, which it does and just as rapidly the gas expands and forced the ram back to its original position - Just like in a gas filled shock absorber. Get it? the "shock" is actually just a ram which raises or lowers the rear end, the accumulator is actually the "shock"!

If you have a very hard rear end when driving, OR if the rear seems to "wollow" or be very soft on the road then most likely you have bad accumulators but don't take my word for it, test them. The simplest way I know is to unscrew the hose going from the accumulator to the "shock" - BE VERY CAREFUL - the fluid is under a lot of pressure and will spray abut a coffee cup of oil everywhere. With the line off slide a small punch into the end of the accumulator, it should go no more than about 1/2 inch in, if it goes 3 to 4 inches in, the diaphram is gone and the accumulator is worthless and must be replaced.

Do not simply gut the hydramatic system and replace it with springs and shocks, you would be replaceing a remarkable system with a very basic one. Once working you can load the car down and have a level ride, you have a system which works better than just about anything on the road and you have no shocks to go bad.

If you need more info let me know and I will help as much as I can. I have a 1989 560 SEL, looks and runs like new with just under 200k...With hydramatic suspension.

Chris

Great explanation, Chris. thanks. This is just what I needed to know.

sjcruiser · #8 01-26-2004, 04:50 PM

Chris,

What tires' brand & type do you have in the 560SEL ? I have the Conti Contact CH95 on mine and they seem a little harsh.

I resolved the rough thump when traveling down a speed bump with newer rear shock bushings.

Any other things to be considered for the ride quality ? I've only been to a few 560's with worse suspension then mine so don't really know how good is a good suspension supposed to be.

cheers,
Frank.

cgoodwin · #9 01-26-2004, 05:28 PM

What is wrong with your suspension???

What are the symptoms?? Be as specific as possible, ince the system is understood is is fairly easy to repair and no where near as expensive as it was in past years, perhaps I can help.

As for tires.... I have studs on right now and as soon as the weather lets up I will probably track down come 18" Monoblocks and maybe run mich's

I don't really want a Ghetto Sled or a Drag car, just a nice 4 door comfort car with enough power and no one does that like Mercedes. Personally, I think the 560SEL was the last of the great Mercedes (sure to catch flack for saying so), it was designed to set a hallmark for all other manufacturers, the styling is classic and refined, the build quality is second to none, at close to 300hp it has more than enough power for anyone over 25 driving on the street.

Paulwho · #10 01-26-2004, 08:21 PM

Shawnster,
"A rear end which is low in curb weight condition should never be set higher by adjusting the connecting rod of the level controller."
"Therefore, if the vehicle is too low in curb weight condition, corrections on rear springs are required."
Excerpts from 40-310 checking vehicle level on vehicles with rear level control.

plutonian · #11 04-05-2007, 09:55 PM

[quote=Paulwho;553075]Shawnster,
"A rear end which is low in curb weight condition should never be set higher by adjusting the connecting rod of the level controller."
quote]

Hi - I read these and Chris's explanations and caveats - maybe too late - in my neigbourhood (Big Sur - rough mouintainous dirt roads) folks drive mercedes 300TD's like mine (an 82) with the level raised to the max by adjusting the leveling rod, to accomodate 225x70x14 AT tires. I can see you all cringing, but the reason for the practice is the terrain and folks want to drive (bio)diesels without having to haul 3/4 ton trucks around and these old wagons are solid enough for the terrain! I just ordered my tires and realise maybe I should be looking for a different solution to the problem - like if you really want to drive a 300TD on these roads, is there a better way to lift the rear the extra inch for the tires and clearance.

Any thoughts!?
Thanks

I guess

cgoodwin · #12 04-06-2007, 03:02 PM

The weight of the rear of the vehicle should be supported by the springs, if you want the vehicle to sit higher, change the springs or simply replace them, it is likely that your springs are pretty tired after all these years. Springs can also be reworked to mke them longer or shorter although in this age of parts replacers actual craftspeople ar getting harder to find, we do have a 70 year old spring smith in Seattle who does work for me.

dieseldiehard · #13 04-06-2007, 03:22 PM

You can carry quite a load in a TD with a good SLS, but you don't want to park with that load for a long time it places a strain on the valve, etc. I moved about 600 lbs of tile on two occasions using my '79 300TD, the SLS was maxed out to maintain level, and I drove very slowly but it performed admirably

There may also be thicker spring pads for the TD if yours is sagging, why don't you check with Fastlane? these go at the top of the spring where it meets the body cup and allows adjustment of ride height without resorting to new springs.
I tried that but I eventually had to order springs made of thicker wire for my 115 which has an air compressor and the battery moved to the trunk (plus the tools I seem to carry around in it, it was almost dragging the ground!)
For any special springs I suggest Coil Spring Specialties, St. Marys KS check them out! http://www.coilsprings.com/index.html

plutonian · #14 04-24-2007, 01:07 AM

Well those + size tires fit just fine, no need to raise my ride! The Benz has big wheel arches I guess. Thanks for the advise though. I'm sure I'll be back for more.

whutchens · #15 01-27-2004, 09:59 AM

I first want to thank Chris for his great description of how to diagnose and adjust the self levelling system. That's really useful information!

I also want to disagree with him just a little. Replacing the self levelling system is not such a bad move if you can do it. Although the sls is pretty effective when you put a load in the car (I have a wagon), it does not optimize handling the way a good set of springs/shocks/sway bars and bushings can. I have never changed out an MB sls yet but I have done it on my BMW 735il. The results were great on my 735. It handles like a dream.

I was wondering, with all due respect to Chris, has anybody out there changed their rear sls over to standard springs and shocks. In looking at the rear of my 92 300TE, the problem I see is the shock mounts. The mounting brackets are kinda weird looking on the bottom and I don't know if you can find a Bilstein or Koni shock to fit. When my components do wear out I may make a switch. So if anybody has done this, I would really like to hear how you did it.

William H
92 300 TE