Originally……….I was going for a standard strut, spring and top mount
which I had prepared and (Powdercoated)
Then as the car got lighter and lighter….and my appetite got even more obsessed
with saving more and more weight, the car’s standard ride height just grew and
grew upwards… and so it became clear that an adjustable ride height for the front
and rear was required.
As this is a Road car, Fast Road car (hopefully), possibly an odd sprint / hillclimb
and I may consider doing a trackday then I wanted the suspension to have as much
movement and compliance, whilst having good control and Not rock hard and too low
that most of the movement was lost, which is needed on UK roads as they are not
Billiard smooth are they! So Simple Spax Adjustable (Damping) shock absorbers are
being used and Not anything that’s available that could be too stiff.
The front uses inserts which fit inside the original front McPherson Strut tubes.
To adjust the damping, On the front these have a knob which fits on the top of the
shock absorber inside the engine bay and turns a rod clockwise or anti to stiffen and
soften the bump and ride damping.
The rears have an adjustable fixed knob on the bottom of the leg which also turns
for 14 settings.
I decided to use these steel collars which are welded to the struts, then using a
2.25″ ID Common Racing Coil Spring the lower platform is then adjustable up and
down to set the desired ride height.
Standard 924S / Early 944 strut body with welded threaded collars
Long springs for lots of compliance and a reasonable spring rate at 190Lbs per inch
which compare to 140lbs standard, but this is with a car 250kg heavier
The original 924’s used Steel, and the 944’s aluminium versions which are lighter and stronger
A Porsche design and not the original VW items which were sourced from the VW Golf Mk1 at the time
Porsche designed the 924 for VW in the 1970’s. (Project EA425)
These are the “shorter” (Early 944) fully refurbished & Painted arms sourced from 9Apart with
New bushes and balljoints……
First Roadtest (August 5th 2016)
Yes, ……the car is too stiff for Road use so I need to soften the spring rates and also
consider a better suspension system which has features to assist the ride comfort
I need to do some research and see what’s available or can be made.
I fitted Bilstein B6 Inserts as i thought they might be a little more forgiving than the Spax,
but they are even more harsh!
The top Screwable cap also rust very quickly after 3 months!
Bilstein (Bottom) are Upside down Mono Tube design
The car also had a lot of Bump Steer which needing sorting out, this is where the low ride
height alters the angle of the Steering track rod, as also is the lower wishbone angle not as originally designed which should be parallel to the road .
The plan is to modify a pair of Aluminium wishbones with a Male Rod end like these from a successful Racing 944
The later 944 Wishbones are longer and thicker than the earlier types (924s / 944)..
The longer Wishbone on the bottom has had the original balljoint & Housing cut off
in preparation for the male rod end
Here’s the solution I’ve chosen from the Racecar, which has an M20 Rod end and
extensions including the steering track rod and boxed in welded supports
Here’s some Extensions I’ve had specially made for the wishbone & track rods
Mocked up ready to be welded in, and also have a link bar added between them for
Wishbones done Sept 2017
Stub axles Welded up, painted and a trial fit to a Intrax Front Strut
2nd Hand Aluminium Hubs, stripped painted and ready for NEw bearings
The Extensions both had to be cut a little shorter to make sure they clear the bottom
of a 16″wheel, they will change the 2 pick up points for the Wishbone and steering Tie Rod
by approx 35-40mm
I’ve ordered a full custom set of INTRAX (Holland) suspension
Intrax is a Dutch manufacturer of high-end suspension technology with over 35 years experience
at the highest levels in racing.
Intrax designs and produces shock absorbers, springs and suspension packages for Formula 1 cars,
road cars and everything in between.
In addition to an elaborate street- and competition program, Intrax also delivers “custom-made solutions”.
The custom set being made for the Porsche are :
1K2 shock absorber
A “high-end” shock absorber for demanding street- and competition build using
the finest materials., the housing is made from 7075 aluminium this guarantees low weight,
maximum strength and optimum cooling.
– 46mm body with a 40mm piston and a 16mm piston rod.
– upside-down system with a 40 or 45mm guidance tube for maximum stiffness and wheel guidance.
This is especially important when the G-forces are higher than obtainable with the standard vehicle.
– “Black Titan” coating on the guidance- and piston rod.
( This is a coating that cannot rust and is extreme hard and smooth.)
The friction is lowered with these piston rods, improving comfort, reducing oil temperatures, improving
traction and extending life time under the severest conditions
– ARC (Anti Roll Control)®
After years of development Intrax developed a unique way to drastically reduce unwanted roll
(lateral and longitudinal).
The car can have the comfort and all the other benefits of driving with “soft” springs like extra grip and traction,
until you take a corner or need to brake then ARC® will control ride height with the feel of a sport/race/rally setup.
While driving over a curb, through a pot hole or over a jump the suspension will absorb them like driving with soft springs.
Below is the front & Rear Spax shock absorbers the Intrax set will replace
I fitted the Rear Shocks (only) first before the front wishbones and stub axles are
ready then the front Struts will be fitted too.
Phase 2 included changing the rear springs to softer from 25Nm to 20Nm and also
changing the lower spring pan to a more shallow design, this allows the Helper spring to
still be “open” when the car is at rest which means only the Torsion bar (springs) will
be the only sprung resistance until further suspension is made (Cornering , accelerating, braking)
Then the helper spring will fully quash flat and the main Spring will add it’s rate to the T Bars.
Mock up of the revised and new front strut / Brake / Stub & Hub Assembly
Rubber top mounts
The originals are quite expensive, and the VW jetta component is sinilar but not 100%
as the rubber donut has a tapered shape and the original sits in a Radius.
They are also 10mm taller and will change the ride height accordingly.
(Original of the right) Jetta on the left
Jetta Rubber Mount fits inside, but does not touch the top of the metal but the sides
where the taper meets the metal radius and hence is 5mm from the top bush.
The original needs force to push in and then it doesn’t move.
The Solution was to design and have made some Bespoke Top Mounts that retain a Rubber mount
so these VW Audi Mounts part Number ZBA 412 353 madeby Vibrasil were measured and the new
design consists of a Top plate like the original but with the correct taper shape, but also with a lower
bottom plate which houses and holds in the bush.
The original design has nothing holding the rubber donut from moving out the housing! In reality
the car’s weight is keeping it there, but as I was going to the lengths to have a top plate made to
suit a Rubber Bush, (and not a solid harsh spherical bearing type) I decided to fully enclose the
rubber mount by bolting a lower plate to the top plate which has M8 threaded holes.
4 Stainless Bolts with spring washers clamp the 2 plates together and then protrude
up enough to fit through the chassis like the original design.
CNC machined from Billet Aluminium
Front Aluminium Strut tower Brace, stripped and painted in body colour (Alpine White)
Rear Suspension / Axle / Trailing arms
I initially used Spax dampers, which are normally Yellow in Colour but this would of
clashed with my paintwork on the back axle & trailing arms !!…..
so I choose to paint them Red instead !
Then I tried Bilsteins, they INTRAX
Porsche sourced and designed the rear suspension based on the VW Super Beetle
which uses independent trailing arms, Torsion bar springs, and telescopic shock absorbers
This is the whole rear axle assembly removed from the car……….
The precedent with this car is to replace as many parts with new if 90% necessary or
to repair and refurbish as many as possible Stripping anything down takes little time,
compared to re-assembly and once you start there’s no going back Many items are in a
worst state as you get to them with often bolts shearing off, and rust getting into places
previously unseen. Bushes are worn and paintwork faded etc…..
Having a Paint stripping and powdercoating business is on the plus side very handy,
the only snag is once an amazing standard of finish is achieved (Which is all I do!)
on one item almost Everything else has to follow suit, otherwise it’s pointless
and will not only look inferior but niggle me when the car is done, …………..
Because I’ve very unlikely to take it apart again!
Below is the Lateral Torsion bar tube and trailing arm carrier………having been
stripped in acid and for some daft reason I decided to drill it with 90 holes ………
all for half a Kg saving!
Still……l to be fair coupled with stiffer 27mm thick Hollow Torsion bars from
Elephant Racing (USA) which are 750grams lighter each, the total tube and bars
will 2kg lighter than standard and stiffer….that’s a worthy mod and saving.
Spring plates stripped and coated…..I was thinking of going for new ones but changed
my mind when I found out they were about £240 a pair!!!!
Pretty Aluminium arms in a Graphite Metallic Grey with a clear Gloss Lacquer
and Logo detail…
Originally the spring plates have a Rubber bushing which fits inside the tube,
but these Poly Bronze bearings from Elephant Racing are the ultimate in compliance and
accuracy, they are much better than a hard solid bush which would be too stiff and wear
in time, as they still offer some vibration absorption from the softer Red Poly and a tight
fit from the bronze / steel race design.
They also feature 2 major details, where the ride height can be adjusted very easy
compared to the original design, each Torsion bar can be inserted in situ to achieve a
close spline location / height. Then fine adjustment to the cars geometry can be done
with the adjustable bolt in the centre…….
The Axle Powder coated in a super tough Satin Black
Then 90 Vinyl Stickers were applied to each hole to keep out the moisture etc..
Chassis / Torsion arms arms powdercoated………..
The New Rubber Bushes wouldn’t fit inside the torque tube arms, So I fitted Poly !
This is the Elephant Racing Bronze bush inserted and bonded in the Torsion tube,
there’s a groove running inside and a Grease nipple tapped in the tube allows regular
lubrication / maintenance
One side of the assembly bolted together………
New Wheel Bearings ,& New OE Rubber Bushes need pressing in the hubs arms then
it’s ready to go back on the car ……..
Manual Racks were the standard spec on 924’s and early 944’s …Power Steering was
an option ………But any Power assisted steering does not feel as good as a Manual rack
and this is no exception…..Tie rod arms stripped…………….and the rack sent off to a
specialist to check and refurbish……
The Engineers report was that the rack was in very good condition and only needed
tightening to spec and re-greasing
New tie rods and ball joints fitted with new Rack Rubbber mounts to the Engine X member
Chassis / Suspension Preparation (August 2015)
J&L AutoTechniks (Tattenhall – UK) installed the front and rear suspension :
New: shock absorbers (Spax) , Brake discs, pads, hardline (Copper & Nickel)
Wheel bearings, fresh ate blue fluid, and painted trailing arms with new bushes
18mm Anti rollbar, 27mm Hollow torsion bars inside the tube laterally
Geometry Set up – Computer Race pads & Special hub plates