W123 self levelling noise

[stuarth]

I have a 240td 20 years old. I have a noise from the back at one side - a cloink when it goes over some bumps but not all bumps and not at high speed. Nothing seems to be loose. How should I check the shockers or bleed them or check the spheres. The Haynes manual is a bit vague on this. Any advice please? In the limit, can I replace the system with ordinary shockers?
thanks

 

[TimN]

If the rear of the car still rises when loaded then there is probably nothing wrong with the system. Damaged spheres would lead to a stiff ride quality. I would look at the condition of the springs. The ends, which are deep within the wells of the trailing arms, have a tendancy to snap off. In fact sometimes there can be multiple fractures of the ends of the springs. It tends to be pretty mucky in the wells which incourages the corrosion but try to take a look and I can almost guarentee that there will be either one or two broken springs.

 

[stuarth]

it doesn't!

The springs seem OK. The back does not rise noticeably. What is the right sequence to check all this? Should I bleed the system and if so, how?
thanks
stuart

 

[TimN]

The system is self bleeding. If the oil in the reservoir is particularly black then suck it out and replace with fresh. You can remove old oil from the rear struts via a bleed nipple on the self levelling valve but make sure that the car is sufficiently high enough as it will come down a long way.

I not sure whether you tested the self levelling right. Open the tailgate and get a few hefty mates to sit on the threshold forcing the back of the car down. Turn on the engine and wait for a few minutes. Give it a bit of a reev if it is struggling. Hopefully the car will relevel in a short time.

With regards to the bags I wouldn't disregard the springs totally as being the cause. After market springs are particularly thin, have more rotations and are generally naff. It causes a sort of boing noise whilst going around roundabouts. Other possibilities are exhaust not hung correctly or perhaps wear in the wish bone bushes.

Best of luck

 

[stuarth]

Can I undo the bleed valve on the self levelling unit, then run the engine, to see if oil comes out? Or alternatively, on the leveling units themselves (from inside the car) to see if oil comes out? What I am trying to acheive is to see if the pump is actually pumping oil into the units or not. Is there a better way perhaps. I sat with two people in the boot but saw no perceptible rise and the level in the oil reservoir does not seem to drop much, if at all - this could be because there is not enough weight though.
Last question - has anybody managed to get the springs our without using the special mercedes spring compressor (just using the type that attachs on the outside like claws)?

thanks
stuart

 

[TimN]

The springs come out simply enough. I did it by unbolting one side of the sub-frame doing that spring and then repeating the same operation for the other side. I did read somewhere that if the dif mounting bolts are released and the diff lowered then you can do both. You won't need spring compressors but you will need a nail bar to lever them out.

In proparation for the job I recommend that you test the unions joining the hose to the top of the suspension strut. They often sieze and twist eventually snapping. If the bolt crack off nicely then you wont have to replace the hose. Don't undo it till you're ready. Just give it an eighth of a turn or what ever the windo will allow as it is holding alot of pressure.

I thought there was nothing wrong with your springs?????

The bleed nipple on the self levelling valve releases the pressure in the spheres and struts. It will only permit fluid from the pump to pass if the valve is open. To do this you need to simulate heavy loading.

If you are getting fluid pumped around and being discharged back into the reservoir I would do the following test with the vehicle up on ramps. Disconnect the adjustment screw on the linkage to the torsion bar (If it doesn't snap). Start the engine and then get back under. Grap the lever on the levelling valve and pull it towards you. If I've got this right and it's 50% the car will think that it is too high and will attempt to level thus dropping. Push it away and vice versa. If nothing happens then either the pump is knackered, the wrong fluid has been used or someone has already tampered with the internal working of the valve or possibly the system has been disconnected and sealed somehow.

 

[stuarth]

Thanks for your advice. I tested the return fluid and undid the control bar and the suspension rises and falls as expected. I also had an MOT test of the 'shockers' a few months ago and it passed perfectly which implies that the spheres and pressure must be OK (correct conclusion?)
I have not removed the springs but they are original and looking into the well using a mirror shows now signs of breaks - I agree this is a bit of a dubious test.
With the seats down, I rode in the back above the axle and the clunk comes from the centre but a bit to one side and is a quite a heavy hit but not on every bump.
Where do I look now? I see and feel nothing loose. Could this be some mountings and if so, which are the most likely culprits?
A mystery but I was pleased to note that after 20 years the bolts come out nicely whereas my Landrover after 5 years was rusted to death and most things sheared...

 

[TimN]

I would start by looking at the multitude of pipes that do into the self levelling valve and making sure that they are either clear of the body of the car or securely fixed. If someone has replaced these in the past they can be a bugger to get correctly routed.

Next check that the rear torsion bar is securely fixed and that the mounts at either side are in good order. Also check to see that the suspension stop rubbers have not fallen off.

If the vehicle is riding low, adjust the height so that front and rear bumpers are the same height from the ground.

Check the mounts on the rear diff for condition.

If none of the above work then it must be something to do with the running gear.

 

[stuarth]

There seem to be two sets of suspension stops. One is near the front of the wishbone (and in my case, they have both come off) and the other in the middel of the wishbone (and in may case, no evidence there has ever been one there). Are these the ones you are talking about?
thanks
stuart

 

[andy_k]

I'd stop looking at the self levelling system and removing the entire rear suspension.

Take a look at the upper links of the suspension my bet is that one of these has worn. They are a known weak link on estate cars (all that extra weight at the back) and (on the W124s at least) been replaced by an updated part from Mercedes - cost about £20 the pair so not expensive and take a few minutes to fit

How to test - have alook at your rear suspension and attach a mole wrench or similar to the upper arms then see if the wrench cn be twisted or moved from side to side - any movement at all and the arms are shot.

See if that makes any difference.

Andy