959 Accumulator Replacement Part 2...

[Wayne 962]

Day two of working on the replacement of the pressure accumulators on the 959.

Original threads:
New 959 Project - Replacing the Suspension Accumulators...
Next Project on the 959: Fixing the suspension bounce...

Here's the accumulator right here (softball shaped canister).


This is the elevation sensor that senses where the car is when it's been lifted up by the hydraulic system. In order to depressurize the system, you disconnect the sensor, set it to "high", and then tell the car to lower itself. It will try to lower itself by sucking all of the fluid out of the system and back into the tank. At that moment, the system should be depressurized and ready to be worked on.


Here's the elevation sensor taped in place.


Now, start the car and lower it. I'm working in the garage, so some flexible dryer hoses are needed so I don't poison the sleeping kids upstairs.


Here's the wheel in the "UP" position. Since the scissors lift is too tall for the car to get under when the car is at the normal position, I needed to put some wooden blocks under it. Otherwise, the car would lower itself onto the lift.


This unique door hides the filler for the hydraulic fluid for the system. Use a hex tool to remove the cap.


Here's another shot of the door.


With the system depressurized, it's time to remove the accumulator. You must use a flare-nut wrench on these types of lines, otherwise you will round them out. That would be bad on this car, as the line disappears deep into the chassis.


You want to keep the hydraulic system clean, so cap all connections. I didn't have any caps handy that fit well, so I grabbed a pen cap and screwed it on.


When I tried to unto the top bolt to the accumulator, the whole thing started to twist. I didn't want to put any force on the brackets that attach it to the chassis, so I removed it first, and then let it hang down.

[Wayne 962]

Here's the accumulator hanging down. I used an impact wrench at this point to remove the top bolt - took less than a tenth of a second to safely loosen.


Here's the unit after I spent a bunch of time cleaning all of the Cosmoline off of it.


Here are the part numbers on the accumulator. The logo on the left is the official Porsche OEM logo. The bottom says LAG. I'm not sure what this means - if anyone knows, then please let me know. The full text is:

959.358.043.00
075-4315-014-617/18
LAG 396

I'm sure these were made for Porsche by another company, or even taken and borrowed off another car or truck that uses them. Anyone have a clue?

[layzee]

Did a bit of digging Wayne, I think LAG is Landesarbeitsgericht Stuttgart (LAG) i.e. a Porsche workers union?

[sc_rufctr]

As always a great write up... Thanks Wayne.

You've probably seen this but here's some specific information on accumulators on a S600 Mercedes.

V12 Uber Alles, Replacing Accumulators (aka Spring Actuators, Nitrogen Spheres) in a W140 Mercedes Benz

[Wayne 962]

Originally Posted by layzee

Did a bit of digging Wayne, I think LAG is Landesarbeitsgericht Stuttgart (LAG) i.e. a Porsche workers union?

Hmm, interesting. Never seen that before.

-Wayne

[Wayne 962]

Originally Posted by sc_rufctr

As always a great write up... Thanks Wayne.

You've probably seen this but here's some specific information on accumulators on a S600 Mercedes.

V12 Uber Alles, Replacing Accumulators (aka Spring Actuators, Nitrogen Spheres) in a W140 Mercedes Benz

Thx, that's a neat write-up. I have a pile of those accumulators sitting in my office at work!

-Wayne

[Wayne 962]

LAG may be Lemforder AG...

-Wayne

[Wayne 962]

For those of you interested in this stuff, I have uploaded the section of the 959 Workshop manual that details the repair and testing of the hydraulic lift system:

http://www.959registry.org/Workshop_Manual/Level_System.pdf

-Wayne

[RWebb]

how does the elevation sensor work?

is it a variable resistance wiper deal?


also, maybe this is a good time to "hotrod" "that old car" by putting a Cayenne adjustable suspension on it...

[spuggy]

Originally Posted by Wayne at Pelican Parts

I'm sure these were made for Porsche by another company, or even taken and borrowed off another car or truck that uses them. Anyone have a clue?

Citroen invented IIRC, and were very fond of, hydropneumatic suspension systems.

My BX19 had multiple accumulators that looked very similar to yours - as I discovered one day when I abruptly lost the power steering and noticed the interior of the engine bay to be awash with hydraulic fluid...


Wikipedia says (some of this may be Citroen-specific):

At the heart of the system, acting as pressure sink as well as suspension elements, are the so called 'spheres', five or six in all; one per wheel and one main accumulator as well as a dedicated brake accumulator on some models. On later cars fitted with antisink or Activa suspension, there may be as many as nine spheres. They consist of a hollow metal ball, open to the bottom, with a flexible desmopan rubber membrane, fixed at the 'equator' inside, separating top and bottom. The top is filled with nitrogen at high pressure, up to 75 bar, the bottom connects to the car's hydraulic fluid circuit. The high pressure pump powered by the engine pressurizes the circuit and an accumulator sphere. This part of the circuit is at between 150 and 180 bars. It powers the front brakes first, prioritised via a security valve, and depending on type of vehicle, can power the steering, clutch, gearchange, etc.

and

Spheres are not subject to mechanical wear, but suffer pressure loss, mostly from nitrogen diffusing through the membrane. They typically last between 60,000 and 100,000 km. Spheres once had a threaded plug on top for recharging. Newer spheres do not have this plug, but can be retrofitted. The membrane has an indefinite life unless run at low pressure, which leads to rupture. Timely recharging is thus vital. A ruptured membrane means suspension loss at the attached wheel; however, ride height is unaffected.

Hydropneumatic suspension - Wikipedia, the free encyclopedia

[Wayne 962]

Originally Posted by RWebb

how does the elevation sensor work?

is it a variable resistance wiper deal?


also, maybe this is a good time to "hotrod" "that old car" by putting a Cayenne adjustable suspension on it...

According to the factory manual, it appears to be a potentiometer of some type. To test the unit you check the resistance coming out of it. So, I assume it's a POT.

-Wayne

[Wayne 962]

I'm sending the unit out to a guy in Texas who repairs and refills these. He's going to check it out with his borescope and determine if we can refill them and be on our way, or if we have to look to another alternative. I think that the Mercedes units will work well, as they are similar in size, but they are slightly smaller. So, if they are smaller, then the control pressure in the bottom of the unit needs to be adjusted in order to compensate.

We'll see...

-Wayne

[m110]

Great write up. Are both dampers hydro-pneumatic, or is it used to augment a high pressure unit?
That whole car reminds me of a Simpsons episode where Homer is trying to repair something at home to save a few bucks by following a video. The Phil Hartman voice says something like: "...now recover the fan with carbon fiber. If you can't find carbon fiber use Kevlar."

[Wayne 962]

I'm not super familiar with these systems just yet, but it is my understanding that the accumulators act as springs, but have no dampening in the system. So, the system is coupled with the standard shock dampener (which I will also be replacing with a new unit from Bilstein). Those shocks are adjustable too - they have a valve that is controlled by a motor that is controlled by a dial in the car (very cool - more on that to come). It's pretty complicated in a money-is-object-we-would-never-build-something-like-this-for-a-production-car kind of way.

-Wayne

[pszemia]

Wayne, as far as i can read, the system is equal to Citroen Hydractive suspension. My dad's Citroen C5, haves a system like this. It works leveling the car in every situation, and also i can select 3 different heights for more or less clearance. Also have a system that makes the car more stable on high speed turns.

here is a pic i found of an earlier hydractive system:

[Wayne 962]

The 959 system is similar, but it doesn't have a return line. I wonder how the system is bled? The manual says to cycle through a few times and it will bleed itself. Maybe there is a return line that I'm not seeing on the car, I will have to look deeper.

-Wayne

[pszemia]

It's strange, there is not return line.

Check this page schemamec, which have the hydractive from late 80's


edit: second thought, thinking in my dad's car hidroactive, i think it works with "doors" and actual pressure to move the car up and down. It uses the same line, and send more or less LHM (citroen specific liquid) to the spheres to move the car up or down. And because those spheres are full of nitrogen (i think it was that gas), when the liquid goes out, the nitrogen fill that empty spaces, making the car go up and other way, go down.

And also, that nitrogen makes the LHM (now LDS fluid), go out.

mmm.. i think i discover how it works.. hahaha

[Wayne 962]

Yes, but how do you bleed the air out of the system when you refill it up? It's a hydraulic system, when you add new accumulators, there must be air pockets trapped in there.

???

-Wayne

[pszemia]

as far as i found, the new accumulators, must be mounted on the lowest position possible, so there is less risk of air. In old citroens, it used to have a little screw to let the air go out.

check this system on citroen Changing the Xantia spheres. ..

[GeorgeK]

The setup looks very much like the BMW self leveling system,for instance in the E34 5 series tourings and M5s. It is indeed self bleeding. You put themon in the lowest position then go for a drive trying to extend and compress sthe suspension fully by driving slowly over uneven ground. Cycling the suspension with the floor jack also helps a lot. provided you get good compression.
Just did that this week on my M5, transfomed the car. These things make the car unbearably harsh when worn.