Next Project on the 959: Fixing the suspension bounce...

[Wayne 962]

Okay, with the idle problem solved, I have the following major projects / items to fix on the 959:

- A/C / Heating control
- Oil pressure sender is intermittant
- 4WD system still giving sporadic errors and beeping
- Bouncy suspension ride

This week, I think I'll try to tackle the bouncy suspension problem. Now, the 959 has two shocks on each corner (eight per car). Four of the shocks are hydraulic-style shocks that integrate with the ride height raising / lowering system. The other two are normal shocks like the adjustable valved PSS9 kits from Bilstein. The hydraulic system has what is called a pressure accumulator on it. This device is a round cylinder, about the size of a grapefruit. There is a rubber diaphragm that is located inside the unit. On the bottom is a chamber filled with Nitrogen. This is what I have been told - not 100% sure if it's true.

So, the problem is that the rubber degrades over the years, and the accumulator breaks and releases the Nitrogen. This device then fills up with hydraulic fluid, and the springy action of the accumulator is defeated. The folks at Orange County Lambo said that they recently replaced all four accumulators on a 959 they still service down there, and it fixed the bouncing problem. I have heard (can't remember where) also that this is a common failure for these cars.

Now, this system is not unique to these cars - Mercedes used something like this on the older cars - a self-adjusting pneumatic system. Not quite a 959, but the principles are the same. Likewise, the pressure accumulators are very similar to. So, I have researched this and found a Mercedes replacement part that looks very similar to the 959 units. The 959 units are supposedly about $2200 each (for a total of $9000). The Mercedes ones are $100 each and look almost identical to the 959 units. So, I ordered some of the Mercedes units, and they should be here on Monday or Tuesday. I will take them and carefully compare them to the 959 units to see if they are similar.

References, here is a link to the pages where the pressure accumulators are located. Front and rear are the same unit, despite looking different on the diagrams:

Item 1:
http://www.pelicanparts.com/PartsLookup/HTML/E_959_KATALOG/404-00-Frame4.htm

Item1:
http://www.pelicanparts.com/PartsLookup/HTML/E_959_KATALOG/503-00-Frame4.htm

Here are some photos of the accumlators on my car (photos taken during the pre-purchase inspection):





I don't have any photos of the rear units.

Here is a photo of the Mercedes accumulator:





My thoughts are that I will put the car up on the lift this week, remove the wheels and inner fender liners, and then remove the accumulators from the car and take a closer look at them. I think that if I take the unit, and seal it and put it in some water, that will tell me the total capacity of the bowl. Then I take the unit and fill it with fluid and see if it fills to capacity (which it shouldn't). If it does, it means the rubber diaphragm is broken and fluid is entering the area that should be nitrogen. If the Mercedes units look similar to these 959 units, then I will probably install them and see how they perform. If they perform well, then I will probably leave them in place, and maybe buy the original 959 units as spares. $9,000 is a lot of money to spend on units that I'm not 100% sure will fix the problem.

Thoughts?

-Wayne

[ischmitz]

I like your approach - way to go. I think it is unlikely that the 959 uses units that are radically different. Let us know what you find....

[Wayne 962]

Thanks for the vote of confidence!

-Wayne

[Jared at Pelican Parts]

Read up on Citroens.

[70SWT]

Been wondering throughout all these posts: with all the additional gear and technology onboard, how much does your 959 weigh, real world?

[richde]

So it's a shock reservoir? It has to be rebuildable, somehow....

Find out the specs and temp, or even permanently replace it with a more modern equivalent while you try and source a new diaphragm? Ohlins, Fox, Penske? Course that would be time consuming and expensive, but it's a 959, right?

[spuggy]

Originally Posted by Jared Fenton

Read up on Citroens.

+1. The one on my BX19 that started spewing hydraulic fluid everywhere looked almost exactly like that. And a quick Google says they're filled with nitrogen as well:

http://www.actwin.com/toaph/citroen/work/sphere.html
http://www.citroencarclub.org.uk/PostNuke/index.php?module=ContentExpress&file=index&func=display&ceid=41&meid=141

They're supposed to be wear items - of course, it cost about $80 for a Citroen one when I last replaced one - but I'd bet lunch the 959 item is produced by the same company - just a question of whether it's a common spec or not...

[RussR]

i've done the same job on a 450SEL. it's the same principle on a mercedes and they fail in the same way (fluid in the sphere where the nitrogen is meant to be) the spheres/accumulators aren't rebuildable but the dampers/shock absorbers are - the pressure they hold is a bit dangerous however! (the pressure was enough that fluid shot out during disassembly that went clean through a rag we were using to protect our hands)

i think febi or beru make the accumulators for mercedes-benz. we paid about $220 a unit in AUD. (they were OEM parts, not official mercedes however)

does the 959 have a damper/shock absorber with fluid in it, or is it like a ring on top?

PS. Wayne - Hello from Australia, just finished reading 101 projects and how to rebuild and modify and i must say they're awesome! nice 959 too.

[VFR750]

You might want to approach the removal of the accumulators with a bit of caution. The system still might be pressurized even though the diaphragm has ruptured.

Or, if one of them is not ruptured, it may when you relieve the system pressure and the nitrogen starts to expand and strains the diaphragm in the opposite direction.

Just be careful.

[JasonF]

Originally Posted by RSflared72E

Been wondering throughout all these posts: with all the additional gear and technology onboard, how much does your 959 weigh, real world?

I was thinking the same thing. Per Wikipedia, curb weight is 3,190 pounds.

[chrisp]

Wayne,

are those blue aluminum oil line fittings stock?

[MarKoBrow]

Wayne, what was wrong and how did you fix the Idle problem??

[Daveinclarkston]

Hi Wayne,

The new Meritor WABCO hyd commercial brake system we released a few years ago includes two accumulators and during the development proceess I recieved a little bit of education from the engineers. The accumulators we use are a mixed gas (Nitrogen is the main gas and I can't remember the second off the top of my head) which slows the migration of nitrogen through the membrane. With the mixed gas the life of the accumulator has a normal life of 12 years and was only about 4 years with just nitrogen. The problem was not with failure of the membrane but the loss of pressure due to the gas migrating through the membrane, which is a normal process.

One thing we did review during the devleopment process was should we make the accumulators serviceable. We elected not to do so due to additional up front costs and additional lenght of the accumulator. Yours look sealed but you may want to check to see if they can be refilled. The other thing that leads to a more rapid loss of nitrogen is high heat useage. We estimated that vehicles opperated in Arizona would see shorter accumulator life than those in Alaska for example.

Also, in an attempt to find the most cost effective accumulator I did find that there are only two manufactures of nitrogen accumulators in the world and both are based in Germany. Ours are from Freudenberg. I sent you a pm with the maufacturing process of an accumulator. Ours have a 75 bar pre charge when new. Not sure about the Benz have vs the Porsche but this may limit what you can do or limit the usage as the gas is lost over time.

9K is a big hit! Sorry to tell you that I think we were paying somewhere in the $30 range each if my memory is correct. I have also sent you another PM with information on storing accumulators. Per the information I sent our manufacture states that while no loss of gas is expected when empty they do not reccomend storing accumulators for more than five years.

By the way did Dirk send you the pacakge with the test pin out box? If not I'll send him a note as I know he gets busy.

[Wickd89]

Wayne,
Just to make sure, have you checked the Audi Allroad version? Since it is VW/AUDi/Porsche it might match up better.

I almost bought one of these (but ended up with a 2.7T A6). This model woul be more current and might have been based on your cars design.

They have a pnuematic ride height system and it kind of looks like yours (i think)..

Check out the first diagram from this link:
http://www.sjmautotechnik.com/trouble_shooting/susp.html

Best of luck.......

[Porsche-O-Phile]

Don't Rolls-Royces use a similar system?

[Wayne 962]

Originally Posted by Jared Fenton

Read up on Citroens.

Hi Jared, good to see you around! Do you have any specific links to the systems on these cars? I couldn't find too much on the web, except that everyone seems to refer to them as the car that goes up and down!

-Wayne

[Wayne 962]

Originally Posted by RSflared72E

Been wondering throughout all these posts: with all the additional gear and technology onboard, how much does your 959 weigh, real world?

I think it's a bit over 3000 lbs. I have the exact spec somewhere, but it's near that number. Not light with all of this stuff on board...

-Wayne

[Wayne 962]

Originally Posted by RussR

does the 959 have a damper/shock absorber with fluid in it, or is it like a ring on top?

PS. Wayne - Hello from Australia, just finished reading 101 projects and how to rebuild and modify and i must say they're awesome! nice 959 too.

Yes, it has one fluid-filled shock and one air-filled shock on each corner.

Thanks for the kudos!

-Wayne

[Wayne 962]

Originally Posted by VFR750

You might want to approach the removal of the accumulators with a bit of caution. The system still might be pressurized even though the diaphragm has ruptured.

Or, if one of them is not ruptured, it may when you relieve the system pressure and the nitrogen starts to expand and strains the diaphragm in the opposite direction.

Just be careful.

Right, there is a procedure in the factory manual for removing these. I plan to follow it and wear safety glasses (as always).

-Wayne

[Wayne 962]

Originally Posted by chrisp

Wayne,

are those blue aluminum oil line fittings stock?

Someone else thought that they might not be, but the guys at Callas didn't say anything about them being non-stock, and the 962 engines at Rennsport (the 959 has the same / similar engine as the 962) have them all over the place. Pretty sure they are stock, but I haven't seen another 959 opened up like that...

-Wayne