Ups & Downs Of Self Leveling Suspension?
 

What is the purpose of the self leveling suspension? What does it really do and why does Mercedes use it in some models but not others?

Besides E class wagons (123, 124, 210, and 211), Mercedes has used it in some versions of the W201, W124, W126, W140, R107, and R129. I get the concept of compensating for a heavy load in a wagon or even a big sedan, but what was the idea of using it in the W201, W124, R107, and R129? Besides compensating for a heavy load, what else does it do? If it has such great benefits in some models, why not use it in all models?

Just curious. Thanks.

Well, it keeps the car level all the time.

The W108/109 chassis had a mechanical system that is usually long gone by now -- and replaced by a simple spring. The W109 had air suspension, too, not steel springs.

The hydraulic rear suspension also rides MUCH nicer than springs and shocks, but is also mor expensive. Usually optional on most models, although not in the US. European taxis almost always have it, keeps the rear from squatting so badly when really loaded up.

The W116/W126 6.9 and other various luxury models had full hydraultic, and many top line sedans have rear SLS (and it's optional on all).

I really like the SLS in the TE, and I think it handles BETTER than the steel spring suspension in the 300D.

Peter

As stated above, basically the SLS helps the rear of the car to be levelled in case is heavily loaded.

But that's really about it. I have owned three T's (one 123 and two 124s) and have driven several sedans of the same line. Almost never in any situation I could tell the difference in ride or handling with and without SLS.

The only time you can feel a difference, is when the SLS system fails and then your rear axle becomes a cement grave and the slighest hole will make it bounce up to the sky. Then, be prepared to mortage your house to pay for repairs. That is about the only difference with this set up and the regular springs.

I admit it, when the Ts were heavily loaded, the ride was smooth and competent. Although, this happened about twice a year. So, were is the advantage???

Thankfully, my S 500 L is Euro spec and does NOT have the SLS.

I think it also helps keep our 190-D 16 valves level when screeming around corners! :D

Thanks. I get that but still feel like I must be missing something. What you all are saying is, for a heavy load, it's nice to have but some sort of engineering overkill? What does this thing really do? There must by more to it. Why would the Cosworth W201 or 500E have it? I really feel like I'm missing something... What about day to day? How fast does it react to changing loads and is it a kind of active suspension? Say I was driving the wagon without a load at 125 mph and was turning, would the SLS compensate in real time according to the load for each side? Is it slower than that? Does it always do both sides equally? On another note, is the real purpose of this thing to sacrifice itself for more expensive rear suspension parts of vehicles that are expected to receive heavy hauling or racing service? Correct me if I’m wrong, but to refresh the system (which will be needed once about every 100,000 miles), is relatively cheap, about $200 for parts (accumulators), $50 for fluid, and a couple of hours of labor. If it prolongs the life of other, expensive rear suspension bits, would it not save cost over time? When I drive the wagon, I feel like SLS has some intangible value that I can’t quite put my finger on. Day to day, what does it really do for me?

The best thing is that you can switch from soft to hard ride...with a push of a button
And you can manualy adjust the suspension hight!
There is no comparison!
Refering to 129

To give you a more serious answer, I'd have to be honest and tell you that I've never really felt the suspension compensate for anything. For that matter, there's a loud banging sound in the left-rear side of the car whenever the suspension comes back out after compressing over a bump. Very loud, irritating, and it hasn't been figured out by my mechanic who happens to specialize in these cars. Go figure.

That may be one reason why so many 16 valve owners replace the rear self-leveling suspension with more conventional ones after they begin to have problems.

"loud banging sound in the left-rear side of the car "

You better think of taking your car to another 'mechanic'
When diaphragm sphere burst loses the nitrogen and there is no 'back up' pressure to support the load on the shock!
There is banging just because there is no pressure...simple as that

1) SLS is used to maintian a level ride irrespective of the load placed in the rear of the car.

2) This was a feature in only a few models because it was considered a "higher end" component, so vehicles like the W140, R129, W124 500E and W201 16v were equipped with it. Additionally, it was added to the T-class because - in theory - these vehicles would be carrying greater loads than the 'regular' sedans.

3) Sport models such as the EvoI and EvoII as well as the R129 had a variation of the SLS which involved hydro-struts at both ends of the car. This resulted in improved dive & squat resistance along with the ability to adjust ride height from the driver's seat. This would be an obvious advantage on the race track and since the EvoI and II were homologation specials, they came equipped with this system.

4) the SLS is not really designed to counteract body roll. the system employs a valve which is connected to the rear swaybar. when the valve opens & closes it allows pressurized hydraulic fluid into/out of the rear struts. the valve is actuated by the rotational displacement of the rear swaybar. That having been said, if there is enough torque applied ot the rear swaybar, it is possible for it to deflect enough to actuate the valve. I have experienced this in the 500Es during hard cornering. you can feel the rear end resist the body roll.

5) The SLS is NOT cheap. Each strut retails for approx $400 CDN. This is why most 16v owners replace the system with conventional shocks & springs when their SLS fails. Another reason many owners replace the system with conventional shoclks is because there is only a certain amount of "drop" that you can achieve by adjusting the SLS in a 2.3-16. remember, these cars had early versions of the SLS. they did not have the full SLS system with ride height control ready for production until around 1988/1989.

6) the loud banging could also be a result of worn rear suspension bushings. The bushings in the 5-link suspension take a LOT of abuse and are subject ot high loads. as the wheel travels vertically, the bushings have to allow it (the wheel) to move in an arc, while at the same time preventing it from mving in an arc. this is why the suspension bushings wear out so frequently. if the bushings are worn, there is nothing holding the mounting bolt to the suspention strut. the bolt is just floating in the eye of the strut with approx 1/2" of play on all sides of it. you may also want to check the swaybar links as well as the struts. noises like a bang or a clunk in the rear suspension have also been traced to worn swaybar link bushings and collapsed bumpstops in the struts.

7) as for why it was not available in all models, i suspect one word would be an adequate explanation: cost. cost to produce, cost to sell (increased retail price), and cost to support the system at the parts desk (greater volume of parts to carry).

Stefano,
Replace the upper shock bushings 2 each side, and you get rid of your problem. Mine did the same thing, replaced the bushings and it`s great now. When the accumulators go bad these get hammered, especialy the lower one. On the top there is a lower and upper bushing replace both.

John

Thanks, John & others.

John: did the loud banging noise on yours occur when the shock was being compressed or extended? In other words, if I go over a speed bump, I hear the noise as the wheel comes back down to meet the pavement as it extends.

The system you are referring to is COMPLETELY DIFFERENT from the SLS fitted to the T series and some sedans as either standard (in some markets for high end models) or as an option (for almost ALL models in most markets).

The SLS just levels the rear axle, period. No buttoms to adjust ride characteristics or anything. No advantages over the regular setup in terms of handling and ride (unless, as said many times before, the car is fully loaded).

It happened everytime I hit a bump. Sounds like the same thing to me

John