Vilhuer

Bad plan, very bad. Having or not having conical washers shouldn't make any difference on resistance to movement. Not initially anyway. They should be used regardless. Your current setup is using outer rim of HD washer to transfer load between alu subframe and bushing. Conical washer is needed to expand that area from bolt shank towards outside. Your current setup leaves inch wide donut of empty space around bolt.

Carl Fausett

That is not correct. There is no empty space around bolt at all.

Please download the installation instruction and view how it is to be installed before commenting.

They can be downloaded here: http://www.928motorsports.com/install.php

PS: I am not married to this design. I'm listening, and there has been enough input to make we want to take another look at my design.
That's why I am going to bring the car in and re-test the for-and-aft movement to make sure the resistance is not excessive.

If it is, one conical washer can go back in. If that does not suffice, I can add a conical washer on each side. We'll see which is best.

Carl Fausett

Found two pics of "pinning the Rear Camber Eccentric"

Drilled the eccentric first on a drill press.
Then put it in the car and set the rear Camber.
Then drilled the aluminum through the hole in the eccentric and tapped for a M6 bolt.
Installed with a drop of loctite, held the eccentric from turning nicely.

Vilhuer

I did before my second comment in post #7. If there isn't empty space around bolt you have invented something worth Nobel price. Maybe this simple diagram helps.

Trust me. You need to add four extra conical spacers. This has nothing to do with how much movement bushings allow or don't allow. Its just to take up that empty space which must exist because you have taken out conical factory bushing centers and replaced them with flat washers.

AFAIK that adjustment is not a problem at all. I have no idea why that would need to be secured. Weissach joint at front end of lower arm is the one which is moving and pinned with extra bolt when angle changes are unwanted. If its movement is larger than what upper arm bushings allow thats a problem what many of us are worried in this thread. Adding extra bolt into camber excentric will not do anything to that problem.

Carl Fausett

Thank you for your diagram. Now I see the space you are worried about.

Remember there is a steel sleeve within the poly bushing (not in your diagram) so the load is not transferred to the bolt in a single location, creating a bending moment. With the strength of the sleeve around it, we focus on the polyurethane to deform to provide the desired compliance.

On the other side of the HD washer, I see the small space you are concerned about. We are using the HD steel washers to transfer the load onto the largest, strongest, outer section of the rings.

I appreciate your concern and your comments. Again, I been driving this without any troubles thus far.

However, I will bring it in (hopefully before the Thanksgiving break) and take some pictures of the available movement with this set-up. If the resistance to movement is too high, I can re-design and
put one or two conical spacers back into the system.

Lizard928

If you still insist on using poly bushings there, then you need to look at how the factory secures them.
They use a cone shaped washer as a safety to catch the arm and hold it should the bushing fail.
You must completely ditch the flat HD washers to regain the for/aft movement, with them you won't have the needed movement.

Vilhuer

Again. Not having or having conical spacers has almost nothing to do with bushing material shore number or upper arm movement. Hope these pictures make my concern more obvious to everybody.

Factory bushing has concave alu center which is exactly same shape as subframe and hub carrier mounting surface.



Replacing this conical shape with flat washer creates empty space between it at subframe and hub carrier.



Basically bolt and nut are holding together stack of parts which has empty space around bolt shank. In factory setup bolt don't have to handle any twisting movement at all as its supported along entire distance. In this aftermarket setup both ends of upper arm have twisting action which is limited by HD washer. Washer is resting against subframe and hub carrier in area which is cast but I think not machined to exact shape like concave area around bolt hole. Is this area straight in all castings? I think not. Is it healthy to have empty space around bolt shank? I think not. Especially when IIRR bolt is 8.8 and not 10.9 or 12.9. Its not expected to have to do anything other than keep stack of parts together. How large contact area HD washer has to subframe and hub carrier? Is it larger than concave spacer area? Its further out than concave area but is it enough to make its movement resisting power larger than factory setup? Simply adding four more concave spacers will eliminate all these questions as long as spacer is tall enough that HD washer completely clears subframe and hub carrier.

What Colin and other are worried about is there any room for upper arm to move in front back direction when weissach joint in lower arm moves. As long as upper arm don't touch HD washers this is fine but it will not take care of my questions.

Lizard928

Errka,

You also miss the fact that this puts stress on the cast aluminum part and risks the bolt pulling right through the cross member too.

Vilhuer

True but there are several problems in this design and fixing just one is a start.

Carl Fausett

I understand your concern. If you could please wait just a moment until I can get the car in and test it and show you, instead of pilling on, that would be great.

I remember when Marc Thomas wrote up his article about pinning the Weissach. It was met with the same skepticism, and comments that the links would break, etc etc. I expected no less here.

Your concerns have been expressed - hold for a minute now so I can get the car in and we can look at it together.

CraigL

I had an issue setting the right rear camber on my GTS. The slot on the carrier that engaged the eccentric was wider on the right than on the left side. I addressed that problem by adjusting the geometry of the eccentric. We welded
material on the far side and remachined the eccentric with a new offset and a larger base circle. It doesn't fix the issue of eccentric movement but it allowed me to set the camber.

Carl Fausett

Before I can answer whether or not the polyurethane bushings restrict movement to a dangerous degree, I needed to re-confirm what the range of movement was.

When the Weissach goes from a very slight toe-out (stock alignment) to its toe-in position under throttle lift; how far does it move?

We set up a hydraulic ram to move the rear suspension in the rearward direction to emulate a deceleration. We did it this way because there are 3 places in the Weissach joint and coupling with the sub-frame that all have compliance in them, and we wanted the accumulation of all of their compliance.

First picture here is the Weissach link at rest, normal position.

Second Picture is the same link in full rearward deflection.

Third picture is the indicator placed at rest, in normal position.

Fourth picture is the indicator showing how far the upper link mount moved during full Weissach travel. It moved 9.7mm

Carl Fausett

These findings are consistent with the internal limits of the system.

This is the rear bearing carrier, and the bolt that holds the upper link and conical washers in place.

Note the size of the hole provided by Porsche. No matter how much compliance the conical bushings provide, when the bolt hits the sides of the hole - further motion is stopped.

These pictures show how much range Porsche designed in to their system at max, and is consistent with our range measurements also.

Carl Fausett

How much range do we need in the system?

Our conclusion is "not as much as you think." We could only get 9.7mm of movement using a hydraulic ram!

We too were wondering if the Weissach went from a slight toe-out (rest position) to something like a neg 6mm toe-in (each side), but it doesn't. It seems to go to just a slight toe-in. Frankly, just preventing toe-out from occurring on decel is probably all they needed to do.

Remember, this isn't an active rear-steer system, it is only a passive rear-steer system.

Carl Fausett

This video shows our rear banana link installed with all the polyurethane bushings in place.

The link has more than enough range, more range than we need.

As to resistance, I am able to move it throughout the complete range with my fingers. It has more resistance to movement than before, as intended, but not so much resistance to where you need to worry about breaking links or fasteners.