Self Leveling cd 220, w202

[Ody]

My cd220 estate (2000 year) began to drip hydraulic fluid from around the passenger side hydraulic sphere return pipe. The connection to the sphere had been so corroded that the 11 mm hexagon had lost its flats. So I cut the return pipe, and removed the sphere. There was no resistance to a blunt object going into the sphere, so the diaphragm was gone. I ordered two new spheres and a new return pipe from the passenger side sphere to the centre T piece. Mercedes said this was part number A2023200872. It came from Germany and is about 1/3 the length of the piece I cut out. Mercedes say it is the right part. My first thought was they had supplied the drivers side, but it is too short for that also.

Looking around various sites on the net I have found others supplied with the wrong pipes for self leveling systems on other classes of Mercedes with some saying they have been given brake pipes without the restrictor inside the pipe.

Further research suggests the self Leveling system runs at about 195 bar which is below the operating pressure of copper-zinc alloy pipes (Kunifer).

My thoughts are that I am going to struggle with Mercedes and that my best way forward is to replace all the 3/16 pipes in the self Leveling system with Kunifer, adding a wire restrictor to both of the return pipes going to the centre T.

Does anyone have other suggestions?

Regards,

 

[hotrodder]

Kunifer/cunifer etc is a copper-nickel alloy, specifically C70600 (aka cw352H, CuNi10Fe1Mn) for the flavour typically used for brake lines. Copper-zinc = brasses [/pedantic]
Seamless C70600 is on a par with brazed steel brake pipes with regards to burst pressure and UTS, has waaaaay better corrosion resistance and ideal for things like brake & SLS pipework

I replaced all the hardlines for brakes, fuel & SLS on my s124 with cunifer several years ago. Didn't bother with the restrictor in return lines personally although others have stuffed bits of coathanger down the tubes etc for example (probably already seen this thread?) http://www.mbclub.co.uk/forums/wheels-tyres-brakes-suspension/136048-w124-suspension-pipe.html

 

[Ody]

Thanks for the comforting reply.

The more I think about replacing all the 3/16 inch steel pipes with "brass", the more it appeals as having seen how rusted the pipes are I would be un easy as to them failing inconveniently or breaking when I tried to replace bits. I have had to use a propane torch to undo the drivers side couplings. Putting new sphere back to bad pipes feels shabby. Much more work but...

I was kinda shocked at the state having previously had Volvos with "brass" that didn't corrode like this and am only slowly getting over the feeling of being had. I wouldn't have liked to have paid full price and seen it decline like this. Still I like the car and how it drives. I have been disappointed with the corrosion compared to my experience on 200 and 700 series Volvo. Even well away from the wheel arch around the centre of the underside there are places were corrosion has appeared in what are now about 10p sized mounds that I am having to scrape, rust covert with Fe 123 and then paint. The near side cill was also sadly corroded requiring Mig. After priming and painting I have liberally sprayed everything with Dinitrol hoping this will slow any subsequent corrosion and hope to repeat yearly. Best to remember the struggles so I don't put off the renewal of anti corrosion treatment.

Regards,

 

[Ody]

Whoops, sorry missed that I had got it wrong with copper zinc.

Yes should have been copper nickel or even copper stainless as Ni, Fe & Mn are components of stainless steel

I.e. Not brass,

Suddenly realised as I was walking the dogs looking at the constellations that I had got it wrong. Apologies.

 

[Ody]

I have now replaced both accumulation spheres and all the pipe work back to the engine bay, but not the last few feet as both seemed good.

I have cured all the leaks and the car rides as I expect, but there is a difference between the height of the rear wheel arch between driver and passenger side.

On the passenger side the measurement is 610 mm, on the drivers side 578 mm, giving a difference of 32 mm which seems a lot to me, but I am not sure what to expect.

To try and correct what I think is an issue, I have opened the bleed valve on the top of the sls valve and got good flow of clean fluid. Previously I have refilled with zhm as specified on the reservoir. The car has been driven about 2 miles since the repair and otherwise seems okay, but I do wonder if both measured heights are too low as the car seems a little low at the rear.

I wonder if there could still be air in the system as the hydraulic Rams are fed at the top and it seems unlikely that any air that was there would be able to escape, my only potential remedy being to slightly crack the banjo connections to vent any air.

Failing that the next thing that bothers me is whether one or both of the hydraulic Rams is faulty and/or the sls valve.

Can anyone help please?

Regards,

 

[Ody]

Realised my problem is likely not the self Leveling system, but instead the rear springs.

I had misunderstood and thought the sls was a suspension system, but I now believe it isn't and will only operate under very heavy load when the load is enough to push the back down. Under most circumstances the sls won't operate and the rear will be carried on the rear cool springs. The difference in height and that the rear looks a bit lower is probably because the springs need replacing.

I can check to see if the sls is working by disconnecting the arm and by moving it up I should see the rear get lifted by the additional effect of the hydraulic fluid and lowered by moving it down.

Regards,

 

[hotrodder]

It is a suspension system, a self levelling one hence Self Levelling Suspension. It's not that different in principle to Citroens hydropneumatic arrangement, the most obvious difference being that it also relies on coil springs to support the basic unladen weight of the car and set a basic ride height. The spheres do virtually all the springing and (along with the pressurised oil) damping and the struts are basically just hydraulic rams used to maintain that ride height regardless of load.

The SLS system is pretty much self bleeding but can take a while if left to sort itself out with little to no extra load i.e. something heavy in the boot and run the engine/go for a drive or (as you plan to test) disconnect the linkage that drives the SLS valve, manually move it to activate the levelling and it should sort itself out if the uneven ride height is something new since changing pipework and the spheres

 

[Ody]

Ah, thank you, Self Leveling Suspension makes much more sense.

I will get under and see if I can raise the car using the lever on the valve.

The other nightmare that came last night was that I had got the flow and return swapped, so if no response to the lever will swap at the front as don't want to deal with the valve connections again unless absolutely necessary. There is some lettering P & T if I remember correctly, but I don't know which should be the feed. I believe I copied the original layout, but got to fretting last night that I had this wrong. Does anyone know whether P is feed or return?

I don't recall the height imbalance before but I stupidly didn't measure it so can't be sure.

Thank you for your help,

 

[hotrodder]

Cheers. P should be pressure feed to the SLS valve, T return to resevoir. Mercedes-benz | iAUTO.lt has an exploded drawing of the hydraulic lines and general component layout. It shows the pressure feed as being the lower union on the SLS valve which matches the markings on this pic of the valve (2023200058)

32 Suspension while that link's specific to the 124 and some 201 models the principle and many of the SLS parts are identical on other models of MB so may be useful

 

[Ody]

Thank you!

I have been under and moving the lever had no effect and I have the pump feed going into T! Stupid mistake.

I will swap the pipes near the front wheel, this and all the undoing of what I thought was finished being a suitable punishment for making such a mistake. Hoping the punishment doesn't include a new valve because my wrong connection damaged this one.

Regards,

 

[Ody]

Disappointingly having got the pipes correct, there was no response to the lever on the self levelling valve and the left right asymmetry remains.

I believe there are four potential causes:

1) Air lock

2) Failed valve

3) Leak

4) Kinked pipe

There was a small drip on the valve and tee piece, but the level seems stable, so if there is a leak it is a small one.

Ever since I have had this car I have found it rather uncomfortable on long journeys of over about 100 miles. Perhaps this is been caused by a failed valve, but other people writing on the net have noted that C class of the 2000 model year were not particularly comfortable so this may be a red herring.

I noticed I kinked one of the pipes but don't think it is blocked as the system seems to be cycling fluid. I did not use a wire insert which might have helped to prevent a kink but I think it is okay although I cannot be absolutely certain.

I wonder if people who have more experience of working on Mercedes could hazard a guess as to the most likely cause of the problem. The vehicle was made in 2000 and it has covered about 168,000 miles.

I plan to run the car for a few weeks while monitoring the hydraulic level to see if it is falling and/or if the left right to assymetry vanishes.

I need a rest from work in the slutch, cold and rain underneath the car to recover my enthusiasm for this task. Unfortunately I have also discovered that there is a hole in the offside rear sill which I will need to weld up and also that an aluminium AC pipe has cracked so I will need to repair that as well and see if the system can be refilled. Sometimes I have regretted buying this car!

Regards,

 

[Ody]

The mystery deepens.

I have been driving the car locally, no problems other than a very small drop in the fluid level, mm per few weeks.

Then today find most of hydraulic fluid gone.

Vexed, but realise this must be a big leak so easy to find. But could not find any leak except for a tiny bit on the sls valve.

Top up. Drive car about 2 miles, fluid down about 1/2 inch. Look for leak, nothing. Friend jumps up and down on tow bar with engine running while I look for leak, but nothing visible.

Drive home and the level hasn't changed.

The previously mentioned drivers side rear lower by about 30 mm relative to the passenger side remains through out all of this.

There seem to be a few possibilities:

A leak that opens and self seals by some strange mechanism.

Air some how finding its way out

Internal leak in the hydraulic strut

But no clarity as to how I might figure out which or another that I haven't thought about.

I have left news papers under most of the joints and will see if there is any fluid on them tomorrow.

Anyone have an idea what is causing this behaviour?

Regards,

 

[Ody]

Mystery solved.

Overnight there was no leakage measured on papers beneath the car.

So took it to a garage with a four post lift.

Engine running, no signs of leak save little drip on bottom of valve.

So disconnect the valve lever and move to simulate load.

Car slowly lifts up as expected and all is well, till hydraulic fluid leaks from the valve, the tee piece & one of the accumulator spheres joints.

Conclusion: My joints could take normal pressure but at higher load they mostly failed.

This fits with my observation of steady hydraulic fluid level, very tiny leak but then a big leak likely caused by load and/or uneven road and the self levelling suspension reacting & increasing the pressure at which point my flange joints failed.

I did the joints with a low cost tool off eBay which is either not up to it or more likely operator error.

So I either get the chance to get it right a second time with a better flange tool, or I take to an hydraulic specialist.

Regards,