Carl Fausett

We know that the current Weissach bushing was designed to control 1978-era 216/60/16 and 225/60/16" rear tires, and we note it was not changed or upgraded when the rear tires later went to 245/45/16 and 255/40/17".

Since then, many 928 owners have gone even wider than that in the rear, and today's tire compounds have much more grip; creating greater forces for the old, soft, stock bushing that was already over-tasked.

Under these conditions (wider rear tires with stickier rear compounds) the Weissach link can over-react, creating too much toe-in and causing vehicle instability and poor cornering.

Racers have noticed this phenomenon, and reacted by "pinning" their Weissach rear link to lock it in place. That may be reacting too far in the other direction, as you loose the benefits of the Weissach rear link system entirely.

What follows is a different solution to the same problem.

I have developed graphite-impregnated polyurethane rear bushings to replace this old rubber part for you to try. The Weissach isn't "pinned" with this method and still allowed to function as intended. However, these stiffer Weissach mounting bushings will react more appropriately to the higher forces they are receiving.

The bushing I am talking about is #39 in the schematic below.

Prices and more information here:
http://www.928motorsports.com/parts/...h_bushings.php

Enjoy!

dfrhodes

guaranteed no squeaky squeaky?

85euro928

And it doesn't have to be pressed in!

Lizard928

This bushing has nothing to do with the functionality of the weissach axle Carl.

The weissach axle toe changes are caused by the front bushing and the flat spring plate that goes between this bushing and the outer part of the lower control arm.

Replacing a bushing that has 100+k miles on it with new will always result in less movement.
But again, this bushing has nothing to do with how the weissach axle operates.

76FJ55

I agree with Colin, the bushing you are replacing is only designed to take lateral load as the flat plate doesn't transfer trust load to this bushing. The bushing that controls the Weissach toe action is on the outboard end of item 38 where it interfaced with the control arm. The position of item 38 is controlled by the stiffness of the bushing that resides inside the front of the control arm and the amount of thrust applied to the control arm. The length of item 38 also comes into play as it defines the radius about with the front of the control arm move as well as determined the amount leverage applied to the bushing. One easy solution for adjusting the amount of toe generated by the Weissach may be to install an eccentric bushing at the inboard end of item 38. This is provided that you have enough adjustment to still set toe caster and camber in an acceptable range. By installing an eccentric bushing with the mounting hole set to the outboard side you would accomplish both reduction in deflection of the bushing due to the shorter lever arm as well as a decreased radius about which the control arm moves decreasing the toeing effect. You could then effectively tune the Weissach by increasing or decreasing the offset in the eccentric bushing.

Carl Fausett

Quoting Wilhelm Kroniger (the inventor)

Numbers refer to the part drawing below.

Because the transverse link 2 is a leaf spring, the angle it exits the body mount 6 changes depending on the bend of the spring. The bend in the mount is made possible by the compliance built in to bushing 5.
When bushing 5 is made more dense, there will be more resistance in the system.

I agree that the primary Weissach joint is the one we have all been pinning, item "I" in the drawing below. No doubt. However, there is more than one joint in this system that flexes.

So to say that the leaf spring and its mount at 2 and 5 have "nothing to do with how the Weissach operates" is inaccurate.

BC

That link is almost solid on most new cars. They have engineered compliance in but removed the wear items in many cases. Genius.

(Edit) meaning a similar inboard lower arm link, rear.

SeanR

I've replaced at least a dozen of these at the request of customers and found each and everyone to be in great shape and not in need of replacement. Hell, getting the old one out and new one in cost more in labor than the new part with no gains.

What gave you the idea that it was something that is in need of replacement?

Carl Fausett

I tried to explain this in the initial post.

Note that this rubber bushing was designed to perform correctly for a 216 and a 225 rear tire.
Note that as tire sizes went to 245 and later 255's, this bushing was not changed.
Note that many of us are running even wider tires than that....

Then factor in that today's tire compounds are so much better and stickier than the tires of 30 years ago - and know that the resulting forces on this old, undersized bushing are much higher than it was designed for.

Allowing too much Weissach movement, too quickly.

This polyurethane bushing is intended to help bring the Weissach rear end fitted with sticky wide tires back into the proper performance characteristics.

Vilhuer

Doing harder rubber for actual Weissach joint (#38) would be much better solution for achieving correct rear wheel angles with wider tires and slicks. Flat metal rear piece twists back more than it moves towards center of the car and thus affects rear inner bush (#39).

terry gt

Like Colin said , nice bushing , but not the Weissach joint that is sometimes pinned

76FJ55

Does any one know how far the rear hub acrually translates fore and aft under accel and decel?

FBIII

I'm guessing that in stock configuration all the bushings are made of the same material and have similar characteristics under stress. Wouldn't it make sense to change all the bushings to the harder material so that they behave similarly?

Carl Fausett

I also agree that more of the suspension's movement occurs in part #38, however manufacturing a polyurethane bushing to replace that item is beyond our scope.

See picture below.

It isn't a simple piece, and it would require a greater understanding of the part and the Weissach system than I am comfortable with. Then there is the cost of having custom molds made to make a part that in all probability will sell very few pieces. Keep in mind, that when people want less Weissach movement, they have just been pinning it for the cost of a pair of bolts.

So for us, making a polyurethane duplicate of this joint doesn't make good economic sense at this time.

Carl Fausett

News from Porsche: "the part #928.331.085.00 is discontinued. The price was $234.43. "

This is the "Weissach Joint" in the picture above.