Australian 6.9 low in rear but OK in front; also goes to High position at front

[6.9forever]

Hi All -

I've been away for 3 weeks and came back to a very low rear end on the 6.9 (left and right).

When idling, it maintains normal height in the front (even left and right) and also responds to the raised H position at the front only.

There's no leak from back struts so I wonder if the back valve has stopped working while unused for that 3 week period? Or is it another easy fix?

Any help on the initial approach to the problem would be appreciated before I insert blocks and tow to workshop.

Thanks and regards.

 

[Helmet]

Hi David, first thing to check is that the link is attached to the rear level valve . May have broken the plastic ball joint

 

[Oversize]

If the fluid's dirty or has't been changed in years it could be a blockage. If not it'll probably be leak-back through the rear valve since the problem is common to both struts. Carefully try bleeding the system at the rear valve and see what you get.

 

[6.9forever]

Thank you both.
Peter: I've checked link - it's intact.
Mark: I suspect dirty fluid. I will probably start with a drain/flush/refill, before tackling any hardware.
Cheers.

 

[Styria]

Hi David, sorry to be a little slow in responding. Short of checking the system with pressure gauges, one can start checking some functions by undoing various plugs and/or piping to determine if there is pressure, or if there is an air lock.

Am I right in assuming that the aircells have recently been renewed ? If so, the system has probably been disturbed to some degree. First of all, disconnect the wire cable from the disc sitting atop the distribution valve. Ensure that there is resistance when you move the disk from normal to static position, and then to the high position and back again. There must be resistance.

Next step is to undo the 12mm plug that's attached to the control valve on top of the reservoir. Initially, with engine turned off, remove that closing plug, withdraw the very small gauze filter that's behind the plug and check the interference fit of the rubber 'O' ring that is attached to the plug. Once you have cleaned the filter, replace refit plug and tighten firmly. Start engine, observe operation of disc (there should be resistance when turning), and slightly undo that closing plug - not by much, observe if pressurized hydraulic oil will want to spurt out, and if it is, retighten that closing plug whilst engine is still running. Try and take the car for a drive in the hope that suspension movement will " wake up" the system and rtaise the rear level back to its normal height. Of course, please feel free to phone me. Best of luck, Styria.

 

[6.9forever]

Thank you, Michael.

I'm packing to travel again in the morning but will be able to lift the bonnet/hood again on Friday and try this out. There used to be good resistance when turning the disk atop the reservoir. Now there isn't. I had noticed this only recently and wondered aloud if this suggested a fluid problem. No, I haven't replaced the cells yet, although they must be done. Firstly I have to get the old girl up off my garage floor; my younger neighbour thinks it looks "wicked" in its current stance! (there is currently 3/4" clearance under the intermediate silencer!).

She turns 40 in August and I am planning a party with lots of presents (accumulator cells, new tyres, air-cond regas etc.!).

Your sage words are, as always, much appreciated.

I'll keep you posted.

Cheers.

 

[Michel]

I had the same problem with the Red Terror.
Parked untouched for a few weeks and the back is down.
Check the disk and it turns with no clicks and no reaction.
I drive it around the block and left it idle for 20min after and nothing changed.
So I parked Friday week and left it it hoping Styria would come the next week and have a look.
Monday morning I come to work and the back is up in it’s normal position!

 

[Styria]

The vagaries of the 6.9 hydraulic suspension system can be numerous and, more often than not, frustrating. I have always maintained that a 6.9 ought to be used from time to time just to keep "things on the boil", but even then one can be left frustrated in working out the system. 6.9s are now, and have been for quite a while, in the situation that anyone component singularly or perhaps in tandem with other components of the system, can leave you stranded, scratching your head, and causing frustration.

For a long time now I have been rebuilding some of the hydraulic components, with a better than reasonable success ratio. I have done this on a hobby type basis, and a number of my endeavours have been dictated by the need to keep my own "Gleaming Beauty" mobile for the last twenty two years - may even be 23. There are other rebuilders in Sydney, but one 6.9 (David Rollason's) has found its way to a very well known repair business with a wealth of experience going back thirty five years - and I am not talking about our Helmet (Peter). They have been confronted with purportedly slightly weeping front and rear valves, and that repair shop recommended replacement of those valves. Now, I repeat this repair shop bristles with Mercedes experience and suggested to the owner that the valves be sent to Melbourne for rebuilding.

The fact now is that the valves have been returned by their Victorian source advising them that they are unable to carry out the work. They simply don't know how to. So, the suggestion was forwarded that they now be sent to the States, and that's where the owner decided to contact me. As far as I am concerned, that repair shop should not have removed those valves and now rendering the car to attain the status of "VOR", especially as they had no idea of how to deal with the problem. From a personal point of view, I am reluctant to attend to this work as it still involves the repair shop to effect fitting of the valves and getting the car going. My preference is for me to do everything, for the simple reason that even if perfectly operational valves are fitted, the system can still be troublesome. Once you disturb the system, anything is likely to malfunction simply because many components are quite old and inclined to interfere with the proper operation of the hydraulics. All this is a bit long winded, but I can assure you that at one stage it took two of us two days to get the system to raise a car to its recommended height. Regards Styria

 

[6.9forever]

Today was a day of discovery.
My 6.9 has sat on the floor for a while now in a very confined space while I was so caught up (and still am) in work-related pressures that are unrelenting, with business travel and a legal case thrown in as well.
I carved out time on this Sunday to clear all the stuff around the car and jack up the rear.
Sure enough, (and contrary to what I previous thought), Helmet was correct back in February.
The rear levelling valve connecting rod has disconnected due to crumbled plastic ball joints at each end. No wonder the rear wouldn't come up, although after sustained effort, the front has. So relieved.
Now to fit the new spheres that I have promised to purchase as well.

 

[Oversize]

Great news!

 

[6.9forever]

New rear connecting rod fitted to levelling valve block and torsion bar. Car rose up! Now to purchase promised spheres.

 

[6.9forever]

Here 'tis. And the post-fit reward!

 

[Oversize]

Brilliant!! FYI there might be another cell supplier in Sydney, but I’ve yet to give them a call to check prices or availability...