Janurary 2002

Bilstein

PSS-9 Suspension Installation

(993)

By Steve Grosekemper

Recently I had the opportunity to install Bilstein's newest suspension system, the PSS-9 system on a 1996 993 C4S. The PSS-9 system (Professional Suspension System) is a fully adjustable monotube gas shock absorber that provides 9 separate compression and rebound settings. Each shock has two separate coil springs of varying spring rates to provide a truly progressive rate, see figure 1.

Figure 1

Assembled Rear Shock Ready For Installation.
This new systems main goal is to maintain ultimate control between the wheels and the road, something previously only available with full custom race setups. I knew that this system was going to be a great improvement to an already excellent car, but I couldn't wait to get it installed and "test drive" the car.

I started with the front suspension, as it seemed to be a no brainer. I was right; the front suspension was very straightforward. The installation was so uneventful I am not even going to get into any detail. Read the instructions and put it in. That is all there is to it.

The rear suspension however was a completely different story. In the directions supplied by Bilstein they indicate that the top of the rear shocks be mounted to the stock rubber shock absorber mount. The first problem with this is that the mount is designed to support the force of an isolating shock absorber only, not the entire weight of the car. The second problem is that the top spring perch is flat and the bottom of the O.E. shock mount is not, (it is concave). The third and final problem is that a main wiring harness runs directly above the right shock shaft and failure or distortion of this rubber bushing could put the shaft of the shock right through the wiring harness resulting in an instantaneous electrical meltdown.

After I discovered these problems I started making some phone calls to people who have already installed this system. Most people were just machining the bottom of the O.E. mount flat or installing a spacer. While this method would work, I was still not comfortable with the support capabilities of the rubber mount as well as the clearance issues to the wiring harness. Then it finally dawned on me, I'll just call the Bilstein Tech department. They had always been very supportive in the past and I was curious if they were aware of this situation and considered it a problem.

The call was made and I was told that the PSS-9 system is a motorsports kit and may need a little modification for exact fitment. He was right; it was definitely going to need some modifications to work. Lou from tech support agreed to come down the next morning to see what the issues were.

My solution was to simply install a solid monoball upper shock mount similar to the setup that a 993 RS uses, Lou agreed. After several different fitments the best part for this application seemed to be the E.R.P. monoball plates with 10mm x 35mm aluminum spacers installed between the monoball and spring perch, see figure 2.

Figure 2
Spacer Installation

These units can be ordered through Performance Products. They seemed to work the best due to their low profile, giving sufficient clearance to the wiring harness, see figure 3.

Figure 3
Wire Harness Clearance to Shock

With the top mounting issues taken care of, the installation was running smoothly again.The settings for spring perch height needed to be changed slightly from Bilstein's suggestions. The front height needed to be lowered about 20mm and the rear about 15mm from the suggested spring perch height to get the look I was after. The final height I set the car to was stock Euro 993 RS height plus 10mm in the rear. 993 RS's are roughly 50mm lower than stock USA version 993's. After a corner balance and competition alignment the car was ready for its first test drive. The car handled just wonderfully. While the car is quite low it does not bottom out or feel excessively harsh on rough roads.

Whenever you upgrade a suspension system there is always a "give and take". You get better handling at the cost of ride quality. I can truly say that this system gives the greatest improvement in suspension control with the smallest compromise in ride quality that I have ever seen…Time for another test drive!

Good Luck!

 

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