Michael Gibney

Rear suspension question

Have done a search and have some answers but am still not clear on the change of shocks 90 to 91.

The info I have gatherd is:

1. 90 rear shocks are 1.5 inches shorter than 91 on rear shocks.

2. H&R printed catalogue (2004) page 78 shows a picture of the two different scockes, clearly shows that the shocks and the working part of the shock is the same length for each year and that it is the upper section only where the rubbers mount that has the extra length, 1990 is 105 mm and 1991 is 68 mm. This would explain the H&R catalogue showing one spring set number "29813" for 89 to 93 models.

3. As far as I can see the spacing of the 3 holes in the top of the rear spring is the same for all years - is this correct?

4. Adrian's book at page 523 says "they can be installed using non-approved modifications..........."

So, my question.... what are the modifications that Adrian hints at?

The reason I ask is that Koni have good prices and adjustable shock sets for 91 (all 4 front and rear) but cannot supply for 90.

As usual I await the kind advice of those who have "been there and done that".

Regards,

Michael Gibney

jimq

The red car is the old style and the white car is the new style. Hope this helps

Red rooster

Michael,
The 91 has the rear , top damper mount lower . That was to accomodate the Cabriolet fold down. That makes the 91 rear damper a little shorter on full droop.
I dont think that ties up with your numbers ?
The 91 three top mount holes are on a little larger radius . I put 91 top mounts on my 89 C4 and had to make a spacer between the 91 top mount and the 89
body holes to get the radius right.
I dont know if anyone has put 91 rear dampers on a 90 rear using 90 top mounts but it certainly looks possible. Maybe the full droop will be a little less .

Geoff

Michael Gibney

Hello Jimq,

Yes, I have the same as the red car.

I am begining to think that the "update" is nothing more that a bigger and better rubber bush system to reduce the noticable "harshness" of the rear suspension of the earlier cars.

Can anybody comment on that?

Michael Gibney

Hello Red Rooster

Does "full droop" = "fully compressed shockers"?

Also, I think you have answered my question because 89 and 90 are the same so if you fitted 91 to 89 I can fit 91 to 90.

I would be interested to have a description of the spacer you mention.

I had not considered the cabrio angle.

Interestingly at page 8 of Adrian's book it shows the two shocker towers and yes the tower looks lower in the 90 on sketch but the overall height looks the same as the 89-90 because the shocker sticks out further.

Red rooster

Michael,

Full droop means jacking up the rear body and seeing how far down the rear wheel droops .
I didnt use 91 Konis as I had 89/90 Konis ! just used 91 top mounts for a whole different reason.

The 91 tower is lower than the 89/90 . Because there is only a small difference between 90 and 91 it MAYBE ok to put 91 rear Konis on a 90 car ?

Maybe someone has tried ??

Geoff

rob964.c4

It is done with mine car, I didn't do it myself so cant explane wahat is exactly done, but I believe they relocated the monting holes.


robert

Colin 90 C2

check out http://www.porsche964.co.uk/technical/rs_suspension.htm

it looks like quite a project. I considered doing this but eventually ended up using Bilsteins, after only finding 1 koni rear in existence.