Bumping an old thread b/c I'm pulling together an order and wondering if the general consensus has changed on this or not. By general consensus I mean my read of the above is that most people have not changed these bits b/c the appeared in good shape. I know the benefit / cost analysis is always up to the individual, but again I'm curious if anyone's thinking has changed over the last 5 years.

 

I had Stan replace essentially all the rubber parts in the suspension of my 150K mile GTS (exceptions: Front A arms that had been assessed as 'good' by Greg B, and the rear sway bar bushings {bar to body interface}. EVERYTHING else that contains rubber was replaced.
Pretty expensive list of parts, but the car rides and drives extremely well, and I've never had a 'true feel' of how the Weissach bushing functioned on a new 928 before. Fabulous difference with the newly available aftermarket rebuilt part.

 

They 'appear' good, but eyes are not durometers.

Replace them, a whole level of vibration and road noise goes away, it's subtle, but does.

 

After doing months of suspension research (and improvements), we have completely changed what we used to do.
Here's a picture of an old upper spring support and a used one (Not even the worse one we have measured.):

928 Front upper spring perches. New on left. 75,000 miles on right.

Now do a cross sectional engineering drawing of the spring support and the shock mount.
Calculate the amount the spring mount moves, versus the amount the shock moves, without corner load. (It's a different ratio, BTW.)
Start adding in spring force per centimeter of movement and shock force per centimeter of movement, using the proper wheel rate and corner weight.
Then calculate what occurs on rebound.

Let me know how important the upper spring mount is....
And how incredible it is that Porsche used the same upper spring mount from 1978 to 1995, as the corner weights radically changed.
The original front suspension engineer was a fricking genius.
As the cars evolved, he was obviously no longer involved.....

 

Ok that is a very good piece of insight. Thanks for sharing. If we can get a measurement of the new strut bearing, then users can compare the compression with their old ones.

 

How long until Anchor introduces their liquid-filled front upper spring mounts, and how long until the first one leaks down the shock?

 

Michael et al,

Stan measured a difference of 10 mm (as I recall) between the height of the strut bearing he removed from my '95 and the new one he installed( about 2 months ago).

Gary

 

I did this. Posted here:

https://forums.openroad.site/viewtopic.php?t=2023

But, go there real quick before this post and that link get deleted.

 

Thanks to all for responding today. Very helpful and interesting. Greg’s pic above and Dave’s thread speak volumes. Reminds me of MM comparison shots.

A question on parts numbers. I see 928 343 047 08 referenced above, but my PET shows part number 928 343 047 07 as the correct part number. Which one is right for a ‘90 GT?

 

"75,000 miles on right."

The more important question is age, miles isnt as important as vehicle weight just sitting on these.

 

Since the newest 928 made is almost 30 years old.....and it has the most front corner weight, age is fairly moot.
They are all crushed.

There is a bit of an issue in installing new ones...tough to get the car much lower than factory specifications, which not everyone will enjoy.
We tossed all of these parts in the trash in redesigned the entire top of both the front and rear suspension, for the Extremely Extreme 928.
Got lucky. That car is insanely "hooked up", with gobs and gobs of suspension travel in both directions.
I made several sets of the pieces we made, but we just have not had the time to install and test on our "street test mule."
.....Kinda waiting for out trick street shocks to be done.

 

Bumping for this question. Anyone know why the discrepancy in part numbers? I see both available. Thanks

 

Order 928 343 047 07 and you will get 08. It’s a parts number supersession, happens all the time. You version of PET is at least two years old.[/b]

 

Thats why I stay online. autoatlanta.

PET;s cool, just turned into a PITA.