W124 200TE - rear Self levelling suspension

[Vectrolosys]

Hello,

Hopefully a quick question.

Very nice as my self levelling suspension is, there will come a time when I need to replace a lot of the pipework and possibly the spheres.

Now, I rarely load the car up and usually only every carry my dog in the back, so the self levelling is rarely getting a workout.

I was under the car today, doing some de-rusting/hammeriting and changing a fuel filter. I noticed that there are some rear springs fitted, plus the struts for the self levellers, in place or where the shock absorbers would normally be.

My question is:-

If you wanted to get rid of the self levelling system on the estates, are there a standard, drop in replacement shock absorber that could be fitted?

Many thanks in advance,

James

 

[Vectrolosys]

Hello,

Having read some other threads on here about this, I think the general concensus is to keep it as it is.

The reason for my initial question was that I noticed the pipework has started to get quite flaky, I've scraped away the worst and hammerited it for now, but, not knowing how thick the pipework is, I have a feeling it's start weeping at some point.

James

 

[Number_Cruncher]

Yes, I've been rustproofing the pipes on the self levelling suspension of our E300D. I shocked myself by looking at the prices MB chrage for replacement pipes.

However, there isn't anything too odd about the pipes or their connectors, and if you did have trouble, I'm sure a hydraulic specialist would be able to make replacements far cheaper than the original reploacements.

There's even a flexible section between the lip of the rear wheel arch and the hydraulic rams, so, it might be possible to replace the whole run with more flexible pipe.

Once you've protected the pipes, the most likely failure will be the accumulator spheres - I'm fairly sure those on mine would benefit from replacement, as I think they are beginning to "bottom out" on larger bumps.

I wouldn't consider replacing the self levelling system - when it's working properly, it's one of the best features of an already good car.

 

[Dieselman]

Just keep applying rustproofing every now and then and the pipes will never need replacing. Spheres make the suspension go bouncy when worn out.

 

[Number_Cruncher]

>>Spheres make the suspension go bouncy when worn out.

Yes, that's one failure mode, where the damping valves in the accumulator fail.

The other main failure mode is simply leakage of the gas through the diaphragm, which eventually escapes via the reservoir. As the gas in the accumulator acts as a spring, the symptom is suspension thumping over bumps.

Effectively, the accumulators provide *all* the damping for the rear suspension, and some extra springing to complement the coil springs - the accumulators can fail so as to provide no springing, or no damping, or neither!

 

[Dieselman]

When the gas is depleted they will go bouncy as the tyres will be acting as springs due to the damping effect being lost.
They only bump if the diaphragm is ruptured.

Trust me, I've worked on a significant number of sphere suspension cars.

 

[Number_Cruncher]

>>I've worked on a significant number of sphere suspension cars.

I don't doubt it, but, I humbly beg to disagree with what you've written.

The system will see no difference between depleted gas and a ruptured diaphragm - both faults will make the accumulator, and hence the suspension "solid".

I watched a W124 estate bouncing along the road the other day, and there's no way that amount of suspension motion (not tyre flex) was happening with a solid hydraulic system. (Although it's entirely possible that some vandal had removed the self levelling system, and replaced it with normal springs and dampers)

The springing effect of the tyres is always present - it can't be switched on or off by suspension failure.

 

[bolide]

There are two failure modes for the rear suspension - high & very bouncy and incredibly hard with no suspension at all

I suspect they're both related to bad spheres - there's not much else to fail - but how the two modes are caused by the same thing failing is something I've never worked out

Nick Froome
www.w124.co.uk

 

[andy_k]

last time I replaced the rear hydraulic pipes on a W124 they were about £12 each. Unlike the above suggestion, they are not just "normal" pipes, they have a spring type insert.

to add to Nick's comment, there is also a third "failure" where the return valve in the self levelling system fails and the car behaves like a Citroen and whenever you park it the reat end drops down on the springs

The spheres are designed to last 200k miles according to MB and the struts about the same.

Replacing either is a messy job but well within the capabilities of the DIY mechanic

Andy

 

[Vectrolosys]

last time I replaced the rear hydraulic pipes on a W124 they were about £12 each. Unlike the above suggestion, they are not just "normal" pipes, they have a spring type insert.

to add to Nick's comment, there is also a third "failure" where the return valve in the self levelling system fails and the car behaves like a Citroen and whenever you park it the reat end drops down on the springs

The spheres are designed to last 200k miles according to MB and the struts about the same.

Replacing either is a messy job but well within the capabilities of the DIY mechanic

Andy

Well, as it won't cost the earth, I'll happily replace them when they fail. Having had a look under there a few times, it doesn't look too horrific, plus the bootfloor comes up to get to the spheres.

I'm currently on 150,000 miles and tend to be averaging 4-5K a year, if that. Looks like it'll be rust that gets them in the end, though the hammerite and waxoyl I'll be applying at somepoint, should put that at bay with luck. It's likely I'll have my dream 300 TE 24 before they need doing anyway .

 

[andy_k]

plus the bootfloor comes up to get to the spheres.

if only it were that easy

yes, you can get to the spheres but you have to unfasten them first (3 x 10mm nuts on captive bolts) and that's where the job tends to get messy

hopefully this will be of some use to you

http://www.mbclub.co.uk/forums/showthread.php?t=3256

Andy

 

[Number_Cruncher]

>>ast time I replaced the rear hydraulic pipes on a W124 they were about £12 each. Unlike the above suggestion, they are not just "normal" pipes, they have a spring type insert.

I was referring to the large diameter pipes between the accumulators and the lip of the inner wing - they're about £70 each, , and are just simple pipes. You're right, for £12, it's not worth fiddling about with the small bore pipes.

I didn't know about the restriction in the small bore pipes, but, it makes sense to want to isolate the fundamentally static part of the system from the rapid pressure rises seen in the circuit between the ram and accumulator.

>>but how the two modes are caused by the same thing failing is something I've never worked out

It's because there is more in a Mercedes accumulator than there is in a Citroen sphere. As well as the diaphragm, and the Nitrogen, there are damping valves in the MB accumulators. With failed damping valves, you get a bouncy suspension, and with no gas, you get a rock hard suspension.

I think the big thing most people get wrong on these systems is that the devices behind the wheel that look like dampers *aren't* dampers at all, they're just a hydraulic ram - all the damping is done by the restriction of the damper valves in the accumulators.

Another way of phrasing it is to say that the accumulators are the rear dampers, and the supplementary springs, all in one unit.

Yes, there are other failure modes of the entire system, like the leaking back from the control valve, there's also pump failure.