W116 6.9 Suspension Lines

[CJBenz]

Hi all, I have a 1979 6.9, the hardline that runs from the engine to the rear accumulator is damaged and leaking, can these be purchased or can you replace with steel brake line?

 

[Oversize]

Hi & welcome! You’d have to try to identify the part number & start searching. One from a wreck might also be an option unless accessibility is difficult.

I’d like to know what coating was applied to these. I thought anodising was only for alloy? It doesn’t look like zinc & peels off fairly easily. Could it just be green coloured paint or powder coat??

 

[Styria]

Having been absent from TK for considerable time due to significant private commitments, I felt that now I should put pen to paper, or fingers to keyboard if you like, to feature some very important procedures in testing the Hydraulic System on our 6.9s, and the idiosyncracies that one may experience when the suspension is not doing what it should. Firstly, I'll reply to CJ in Sydney. Don't know who he is (hope is name is not JOE), but I am trying to get around in identifying his problem in spite of the picture on hand. Tricky situation, although somewhat not unusual. I haven't done it, but it would be quite easy to cross thread the nipple fitting if one is hamfisted. The problem usually rests with the Operator. An alternative fitting would definitely be available from a Brake outlet, but you will need to take the nipple and obtain likewise. I haven't been under my car for a long time, but hopefully the damaged pipe may run to a junction that would feature other lines as well. I f there is, your job should be fairly easy.

To answer our friend and esteemed contributor Oversize, the steel lines would have to be powdercoated in that nice green colour. Freshly painted, they look impressive and very professional ! Regards Styria

 

[Styria]

Having gotten that out of my system, I should talk about the many facets to the Hydraulic Suspension system and features related thereto. It is not really surprising that very few Mechanics would not be able to service the system, but also know how it works , and the way a number of components work with each other, and obviously require a certain amount dependancy. If, for instance, one thing is faulty, other components are likely to be affected. The Workshop Manual, as issued by Daimler in days gone by, is quite instructive, but you would have to be pretty well "switched on" to make head over tails out of it. To be brutally honest, many times have I scratched my head in order to follow the instructions and explanations, such as they are.

I have owned my Gleaming Beauty since about 1994 (yes, thirty years !), so it did not take long to realize that I needed to be able to diagnose which item would be at fault if, for instance, the car goes down in the front or back, if the ride was uncomfortable and bouncy, and no amount of revving would raise the car or , worse still, the suspension would collapse or not hold after the car has been jacked up for maintenance and repair purposes. I have banded together with a very good friend of mine, He has been a 6.9 owner for probably even longer, and between ourselves we realized that we just had to get to know the ins and outs of the whole system. This was probably about ten years ago when we got our heads together, after having taken a full day and a half of working and experimenting before, all of a sudden, the car would raise without warning but to make matters worse, we had no idea how we achieved it. However, success had never felt that good. Presently I am at work, and I may continue a little later when time is more convenient. Regards Styria

 

[Styria]

To continue on. Gradually over a period of time, Chris (fellow 6.9 owner) and I realized that a concerted effort was needed if we were to deal with the system's foibles and idiosyncrasies. Initially, the idea was to copy the equipment and gauges as illustrated in the Mercedes Workshop Manual and I approached a specialized Hydraulic Shop to implement and loosely copy the system as used by Mercedes themselves. So we set to work on my 6.9 (Gleaming Beauty) and it became a task of patience and considerable study to ascertain how the system actually works not only in real life, but also in theory. As we learned and became more familiar with the various components, further testing equipment was devised, and this is kept in a special container that Bryce was kind enough to photograph during a recent visit to my premises, and he was kind enough to offer inserting the photo in one of my posts. It would probably be appropriate that we chose this particular post for the time being.

Right at this time, we use Gleaming Beauty as a testing mule for the various tasks that we are able to undertake in testing the various components that make up the system. They are as follows:

Oil Pressure Pump - it is the heart of the system. Sometimes when there is no pressure in the system as indicated by the movement of the disc on the distribution valve (attached to side of Pressure Regulator), it pays to disconnect the flexible Oil Hose that delivers oil to the Regulator to ensure that there is no air in the system by running the engine and pumping oil directly into the Oil Tank. However, this simple procedure is not an accurate guide as to the capacity or efficiency of the pump. This can only be measured by running the pump under PRESSURE condition and our equipment enables us to determine the strength and efficiency of the Oil Pressure Pump. Under certain circumstances we can service the pump in order to build up the required pressure.

Pressure Regulator - generally, it is a fairly trouble free, but in the event of total or partial failure this will obviously affect the complete operating efficiency of the hydraulic system. Again, we have the means of testing the unit, and also renew various components in an effort to rebuild the unit.

Distribution Valve - I regard it as the nerve unit in the system. It lets you choose normal and high setting, but it also incorporates a "NIL" pressure feature that enables you open up any of the connecting piping that connect to the front and rear suspension valves, as well as all the five Pressure Cells, four of which perform the function of Shock Absorbers and control the quality of the ride both front and back. In addition, it also controls the fifth Pressure Cell that replenishes additional oil to all other components if there is loss of pressure in the system. The distribution valve also controls the function of locking the system and preventing the suspension from collapsing after the car has been jacked up. That feature is built into and part of the front and rear suspension valves. Very few people will understand how this part of the operation works.

Pressure Cells - they are the units that provide you with the required comfort that should be part of the system and the quality of ride that an owner should expect from a suspension system in good condition. As most pundits/owners etc. are aware, nitrogen gas and oil are contained in the Pressure Cells but, over a period of time, increasing quantities of oil will permeate the pressure cells, and it is a simple phenomenon that they become rock hard and unserviceable. Some personnel consider the use of the "screwdriver test" as a guide to test the quality or effectiveness of a Pressure Cell's condition - that's totally wrong and really tells you absolutely "ZOT". We can accurately gauge test Pressure Cells with our system and are able to determine as to how close they are to satisfactory operating conditions without removing them from the car. It is our estimate that about 25 atms is just about acceptable before they require replacement. Fronts are 75atms and rears 60 atms. That's about what one should be comparing with when assessing quality of the Cells. BTW, that also applies to the fifth cell that's located under the left front guard. More to come. Regards Styria

N.B. Particularly relating to the front and rear levelling valves.