raygreenwood wrote: On the 412...and any "modern" strut based vehicle, there is very little or no compression of the actual strut cartridge while the weight of the vehicle is on the strut. This is because strut height at rest...is set by extended length of the strut cartridge at the end of its stop. This is also why the 411/12 has the nose high position.
This is the point where I think I humbely disagree:
Even when my model '74 412 is fully empty and low on gas, there is always some compression of the strut.
If not, then when I would lift the car with the car jack, lifting the car an inch, would immediately lift the wheel an inch of the ground...and it doesn't.
Its cartridges were too long. They were a design flaw from the start.
The long travel of the front suspension was done very purposely for comfort reasons (and it worked very well in that respect), or so I understand from the many road tests by german magazines in those days, which partly got their press release info from VW themselves.
This is quite well described in the book 'Die grossen VW' by H.G. Mayer-Stein, which is a book exclusively about the type 3 and 4.
The extra extension was made ...for the extra damping length from the longer stroke so that when the front end is fully loaded...it can handle the weight.
Yes, I also think that this was the case indeed.
The mis-calculation in this.....was that when you have afully loaded trunk and hit a dip at speed.....the enertia of that weight ...rebounds to far...extending the strut cartriidge to its former fully UNLOADED length. That is the main reason for loss of rebound ability in teh 30K mile range on stock dampers. The rebound damping was too soft and the rebound length too long.
Yes, I agree here as well and that is where the Koni shock comes in. Even in the most soft position, its already stiffer than the original vw shock with the oil in the strut. But that might also be just the age and subsequent aging of the original 35 year old fluid/oil.
Another proof of the oil being aged and now too thin is that the Koni schock should be equal in damping in its lowest setting as the original.
It damaged the upper seal on ALL of them.
Well, I just take a very good look at my original shock and its not damaged internally and still seals fine. Damping was also still there, but a little too soft.
So, instead of changing the valving by using another type of shock like the Audi one, you could also use a slightly thicker oil to fill the original shock with
I know you have tried this before Ray and never got the oil-type or the amount of fluid right I believe. I did this some years ago with a 1303 original vw shock and that worked very, very well. I believe we used a hydraulic oil.
Its just an option for those that don't have a Koni shock thats worth a try, since its almost cost-free and as we don't have that many option shock-wise.
Since the strut spring as assembled on the bench....has preload...it fully extends the cartridge. It 100% MUST do this.
Yes, I know and that will be my starting point.
Besides, its mandatory with our yearly (safety) inspection, so don't worry bout that
Lowering the spring perch on a given spring...reduces preload. yes...that "might" lower the car...
Not 'might', trust me, it does.
if there is enough weight to then compress that spring down. But...since at rest ride height is goverened by the full extended length of the strut cartridge...and not the spring compression level....that will mean that you have slack in the strut cartridge like I listed above.
As I mentioned before, thats where we disagree. There
is a fair amount of compression of the spring at rest, so there is a fair amount of preload. The shorter spring will just lessen the preload, hence lower the car. It may not be that much, but lowering this way is really just using the margins that are there.
Its not rocket science, but we just have different perspectives of things I think.
If you want to lower....on ANY strut system....you MUST...go with a strut cartridge with a shorter fully extended length.
No, not MUST, but can.
The ideal is to go with a shorter cartridge ..then lower the perch to keep the preloaded compressed length of the spring on the assembled strut...the same as it was.
I fully agree here! That would be the ideal situation, but lack of shock options limits us in that way, as we all know too well.
Thinking out loud, IF you use a just too short a spring, you may even have to set the bottom perch a tad bit higher, as to not unseat it at full extention...
Using this method with a stiffer shock will lessen the chance of unseating the spring: The time necessary to go to full extension when the wheels come of the ground...(whats the chance of this happening when you won't go off-road driving...?) will be less, so the Koni helps here as well.
I have examples of every production strut tube made for the 411/412. There were very slight differences through the years...but not in the measurement from the lower perch to the spring plate. There was no factory lowering.
No, of course there is no factory lowering! I wrote that it was a factory test-vehicle with a 100 hp 914 engine. I assumed that made it clear that such a car has never been in production..(duh!
)
I mentioned the article before:
http://www.shoptalkforums.com/viewtopic.php?t=90482
If Porsche engineers experimented with lowering the spring perch...then what shorter cartridge did they use? Thats the inmportant part to know.
Well, the Gute Fahrt article didn't specify on that, as is to be expected from magazine articles in general as we all know too well. I already was pleased to learn
what they did to lower that car back then in 1973!
If they did not lower teh perch
Yes, they did lower it. I tend too believe Gute Fahrt in that respect. Its a quality magazine, (still) sponsored by Volkswagen themselves...so the following is not relevant:
...then they greatly increased teh preload pressure on the spring. This spring does well with that to about 1.5" or so...max. Then it starts breakinbg things. Been there..done that.
So then again...what new ball joints and radius arm mountings did they use along with the lowering of the spring perch and the shorter cartridge?
Not really relevant as they did lower the perch; see the above.
The stock springs are huge...and stiff as hell..with a large amount of factory pre-load on them. Much more than the stock cartridge could handle. Ray
No, I don't agree here. I know you think this, but I believe that the american public has a different taste in what a stiff spring is, then we europeans in general do.
If I press on the front of my empty front trunk, it compresses SO easily (and I have the blue , latest, most stiff factory springs) . It is also very comfortable, but it would benefit from a little more spring for my tast AND a better shock.
With the bmw spring and Koni shock, I think I have both grounds covered.
Whenever a spring pre-load is changed, or a spring rate is increased or decreased.....a corrsponding change MUST be made to valving Ray
Yes, I really agree here, like said above here somewhere already
Thanks for taking the time Ray to inform this stubborn guy,
Walter[/url]
