Suspension

Front Suspension

Originally……….I was going for a standard strut, spring and top mount

which I had prepared and (Powdercoated)

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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.

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Standard 924S / Early 944 strut body with welded threaded collars

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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

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Wishbones

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……

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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.

Update:

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!

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Bilstein (Bottom) are Upside down Mono Tube design

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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

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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

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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

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Here’s some Extensions I’ve had specially made (Westminster Engineering Wrexham)

for the wishbone & track rods

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Mocked up ready to be welded in, and also have a link bar added between them for

extra strength

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Wishbones done Sept 2017 by JEMX Remedies Cefn Mawr

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Stub axles Welded up, painted and a trial fit to a Intrax Front Strut

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2nd Hand Aluminium Hubs, stripped painted and ready for NEw bearings

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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

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June 2017

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.

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Below is the front & Rear Spax shock absorbers the Intrax set will replace

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I fitted the Rear Shocks (only) first before the front wishbones and stub axles are

ready then the front Struts will be fitted too.

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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.

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Mock up of the revised and new front strut / Brake / Stub & Hub Assembly

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Rubber top mounts

The originals are quite expensive, and the VW jetta component is similar 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.

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(Original of the right) Jetta on the left

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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.

 

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The original needs force to push in and then it doesn’t move.

 

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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

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These were designed / drawn and made by Dave @ FP Engineering Wales 

Powdercoated  and fitted inside a piece of chassis / turret

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However when fitted on the struts there was some play in the bearing which may be

normal and acceptable on a production VW Jetta, but it was not good enough for my

standards and the application.

So after much thought I found the orginal top cap fits nicely underneath the Rubber

bearing, and then with (2) 14mm ID thin thrust bearings fitted between the top of

the Spring pan and the OE Cap when tightened the play was taken out and the whole

top mount assembly was not only very sturdy without the previous wobble but also

it rotated on the thrust bearings nicely so that the entire Shock / piston and spring

assembly will rotate all together when the car and strut turns on steering lock.

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First Trial Fitting Oct 2017

The bottom of the wishbones had to be trimmed to have clearance from touching the

lower wheel rim on lock, the rod end extension was cut shorter and misalignment spacers

fitted to eradicate the rod end fouling when on full droop

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But the strut still needed to be raised also to make sure the wishbone angle when the car

was on the ground at rest would be parallel, so the bespoke Top Mounts rather than

fit them up inside the chassis as intended they were fitted above the turret and with some mock up

spacers obtained a good position to give the best static positions for the tie rod and

wishbone………

 

2 piece Top Mount (Rubber bearing) mounted on the Top

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Here’s what the Original modified car with the Wishbone and tie rod angles too steep

looked like which produced bump steer and incorrect Roll centre geometry

and (adverse handling characteristics)

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The New set up, totally flat……….

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Steering tie Rods

The New Stub axles extensions are using M14 Rod ends and bolts as opposed to the

original tie rod end which has a much longer make thread, which the rod ends are not

long enough, so a solution was designed and made to have some extensions and to

reduce the tie rod length so that this new assembly could resemble the same length as

the originals and be adjusted for toe settings.

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Painted up and ready to fit

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Front Aluminium Strut tower Brace, stripped and painted in body colour (Alpine White)

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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

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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……….

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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.

 

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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!!!!

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Pretty Aluminium arms in a Graphite Metallic Grey with a clear Gloss Lacquer

and Logo detail…

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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.

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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

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Then 90 Vinyl Stickers were applied to each hole to keep out the moisture etc..

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Chassis / Torsion arms arms powdercoated………..

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The New Rubber Bushes wouldn’t fit inside the torque tube arms, So I fitted Poly !

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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

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One side of the assembly bolted together………

924S rear axle trailing arms shock absorber

 

New Wheel Bearings ,& New OE Rubber Bushes need pressing in the hubs arms then

it’s ready to go back on the car ……..

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Steering rack

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……

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The Engineers report was that the rack was in very good condition and only needed

tightening to spec and re-greasing

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New tie rods and ball joints fitted with new Rack Rubbber mounts to the Engine X member

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Chassis / Suspension Preparation (August 2015)

J&L AutoTechniks (Tattenhall – UK) installed the front and rear suspension :

 

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New: shock absorbers (Spax) , Brake discs, pads, hardline (Copper & Nickel)

Wheel bearings, fresh ate blue fluid, and painted trailing arms with new bushes

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18mm Anti rollbar, 27mm Hollow torsion bars inside the tube laterally

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Geometry Set up – Computer Race pads & Special hub plates

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