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Wayne 962 Wayne 962 is offline
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Next Project on the 959: Fixing the suspension bounce...

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:


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.


Wayne R. Dempsey, Founder, Pelican Parts Inc., and Author of:
101 Projects for Your BMW 3-Series 101 Projects for Your Porsche 911 How to Rebuild & Modify Porsche 911 Engines 101 Projects for Your Porsche Boxster & Cayman 101 Projects for Your Porsche 996 / 997
Coming Soon:
SPEED READ: Porsche 911 (October 2018)
Old 12-01-2007, 10:55 PM
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