RS Suspension Upgrade

Installation of the Carrera RS suspension in a 1990 and 1993
C2
By Bill Gregory and Tom Masino

We both installed the Carrera RS suspensions in our C2’s this winter, and
faced different challenges based on the installation. In Tom’s case, the
installation of a 1992 Carrera RS suspension into the rear of his 1990 C2
presented certain challenges. In Bill’s case, he used the rear stock rubber
mounts with spacers in lieu of the RS monoballs. On the front, while the plan
was to use the rubber mounts, Bill ended up using the Carrera RS monoballs. In
the front we both used the Porsche 24mm adjustable sway bar. In the rear, Tom
stayed with the 21mm non adjustable stock bar for now, and Bill went with a
non-Porsche adjustable 21mm sway bar.

In upgrading a C2’s suspension, there are many choices available. H&R, Eibach,
RUF, FVD, Bilstein, and many others, offer springs, shocks, struts, and sway
bars in various individual and kit configurations. The difficulty in doing it
piece meal is getting things well matched, although there are packages available
from a variety of vendors. However, another option is to use the suspension
parts that appeared on the 1992 Porsche 964 Carrera RS, which, as a non-US
model, appeared in 3 configurations: basic, touring, and racing. All of the
basic, and maybe touring parts are still available through Porsche (although one
part is “not for sale in the US” and must be obtained through a non-Porsche
channel), and represent a balanced suspension approach, i.e.. shocks and springs
are matched. In this article we’ll show you pictures of stock components and the
equivalent RS pieces, as well as some of the special adaptations we each made.
While the 964 factory manual leaves much to be desired, it is helpful in working
on your suspension. The volume you’re interested in is the “Chassis” section.
From a cost standpoint, the Porsche parts are competitively priced with other
vendors suspension solutions.

An important consideration in making the update described below is to ensure
whoever makes the updates is qualified and competent to safely complete it.
Obviously, since we’re not doing the work, we can’t guarantee or take
responsibility for the fitness or success of the installation.

While the parts can be installed in various orders, easiest is to swap out the
front sway bar. This is fully described here on
this site.

The front suspension was the same for both of our C2’s. We used the Porsche
monoball strut tops, the RS springs, and front struts and the “not available for
sale in the US” strut bumper.

 

You can see the entire assembled struts in picture below.


 

Interestingly, Bill received one Porsche-numbered Bilstein strut and one
Bilstein-labeled strut in the Porsche boxes.

Installation is fairly straight forward.

Observations on the Front Install

bullet You’ll need to disconnect the brake line at one point. If you’re going to
dump your old struts, you can just cut out the side of the metal holding the
brake line in place on the strut with a Dremel tool, so you only have to crack
the brake line once on reinstallation.
 
bullet There are various plastic pieces holding brake pad warning sensor lines
and ABS lines that you may be able to reuse. If you have to replace them, they
are not expensive.
 
bullet You will have to realign your suspension after installing this upgrade.
Corner balancing would also be a good idea.
 
bullet Porsche recommends installing new bolts for the strut to wheel carrier
mount – use anti- seize on the first 10mm of the bolt, and on the face of the
bolt head facing the washer, but not on either the washer or nut face against
the strut itself.
 
bullet The top nut that encloses the top of the monoball takes a 1 5/8″ socket.
It has to be tightened to 133 ft. lbs. Porsche warns not to loosen it while
your 964 is on the ground.
 
bullet When tightening the front strut components (as well as any other parts),
torque the parts in increments. Don’t tighten parts to specified torque in one
step.
 
bullet You may or may not need a special Hazet-style tool to torque the top nut
on the strut spindle in the monoball. A crowfoot adaptor worked for Bill,
while Tom took a 22mm deep socket and cut the side open to get the allen key
in. This opening allows the allen hex wrench to hold the center spindle while
torquing the nut to 59 ft lbs.
 
bullet If needed, this is a good time to replace your front rotors, and check the
condition of your brake pads.
 
bullet Porsche directions say to replace the top monoball nut each time it’s
loosened, due to it’s microthread coating. Tom decided that Loctite blue,
coupled with a paint mark on the fitting (to check for movement) would be a
satisfactory substitute, as the top nut lists for $40 each.
 
bullet Also replace the compressible gasket at the top of the monoball between
the monoball and the body, they list for less than $5 each. Your original
gasket is compressed paper thin, and won’t be reusible. The gasket helps to
keep crud out of the trunk.
 
bullet Use anti-seize on the top of the strut rod.
 
bullet You don’t need to disconnect your tie rods or remove the brake caliper
from the rotor. Support the a-arm after removal of the strut.
 
bullet Check your air guides for cracks around the two bolts holding it on. Bill
had one that was cracked almost all the way through.
 
bullet On Tom’s 90 C2, an alignment hole was missing next to the strut opening in
the trunk, so he had to cut off the monoball tab that would have gone in the
hole. The hole was on Bill’s 93 C2.
 
bullet We both have found the front springs can move around the strut, and with
the monoballs, you hear it every now and then. We think this may be more
pronounced while the monoball breaks in. It may be possible to install a
stainless steel hose clamp below the adjusting nut to prevent turning, which
Tom is looking into.
 

Here is the installed strut

The rear shocks, springs, and bumpers (these are available for sale in the US)
can be seen below:

 

 

The
rear suspension upgrade was a particular challenge for Tom and Bill. In Tom’s
case, he found that the 1992 RS components didn’t fit into the pre-1991 rear
suspension. In MY1991, Porsche modified the upper mount by 22mm, changed the
outer tube length of the shock, the rear spring, the protective gator and bump
stop, and the strut mount bolt pattern. To work around this, Tom had a 1.75 inch
spacer made up, whose parts can be seen on the left and installed on the strut
on the right. This adaptor lowered the upper monoball, so everything would work.
In addition, since the rear bolt hole pattern in the pre-1991 models is
different than 1991 and later models, Tom had to transfer the bolt pattern from
the stock mount to the RS mount. Three new holes had to be drilled in the RS
mount and the pressed in studs relocated.



Bill installed the rears first, and wanted to retain the stock rear rubber
mounts as a compromise to soften the impact of the fairly stiff rear springs. To
make this work, the stock rubber mounting had to be cut down so the concave
washer would fit. You can see the concave washer and the stock rubber fitting
below and how the concave washer fits in the rubber mounting after trimming.
When all was put together, Bill found that even with everything adjusted for as
high a body height as possible, that he wanted another 1/2″, so he used a 4″ x
1/2″ aluminum spacer on each side at the top of the mount between the concave
washer and the rubber mount in the bottom picture. This would allow for some
flexibility when corner balancing.

Observations on the rear install
 

bullet

The lower bolt holding the rear shock was torqued 10+ years
ago to 139 ft lbs and is a steel bolt in an aluminum arm. It can take
perseverance to loosen each one.
 

bullet

Use a spring compressor, and observe safety precautions.
 

bullet

You’ll need to remove the air filter to get access to the
right rear fitting. While you don’t need to remove the entire black plastic
airbox, it would gain you easier access to the three upper shock mount bolts.

 

bullet

On the left, you need to remove the engine-mounted air blower.
After that, you’ll need to work over some other fittings.
 

bullet

Push the shock rod into the body of the shock a once or twice
before assembling everything.
 

bullet

This is a good opportunity to replace your rear rotors, and
check your brake pads.
 

Ride: Tom’s 1990 with monoballs on all corners

Handling on the highway was tight and very precise. Although I
have not run the car on the track, I’m sure that the handling will be greatly
improved. The ride, however, is not as stiff as I anticipated. Let’s face it,
even a stock suspension cannot be considered smooth. There’s really no
noticeable difference in ride from the front. Naturally the front is lower and
you have to be careful while pulling in and out of driveways. The rears however
are definitely much stiffer. Bill’s version maybe a little softer with the
modified rubber stock mounts. The rear progressive rate springs are much stiffer
than the stock. Expansion joints are more amplified than before. Small bumps
that were absorbed before are now felt in the seat of you pants. But, put the
car on a smooth stretch on highway, throw in a couple of turns and what can I
say…it is all worth it.

Ride: Bill’s 1993 with front monoballs and rear (modified)
stock mount

Ride on the street is definitely more controlled than the stock
suspension, but is not harsh. I think the modified rear stock mount takes a bit
of what otherwise would be a sharper jolts and makes them more bearable. As Tom
mentioned, you do notice expansion joints more than the stock suspension,
however it’s not bothersome. The Carrera RS suspension is a fine improvement on
the street – it’s too bad that Porsche didn’t offer this as a sports option in
the US. On the track it is a competent dual purpose suspension. One observation:
in high load turns, the rear suspension has to move through the progressive
portion of the spring for the suspension to take it’s set. With front and
[larger] rear adjustable sway bars, it’s fairly easy to dial in a pretty neutral
attitude.
 

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