Polyurethane Rear Upper "Banana" Link Bushings
11-22-2013, 12:39 PM
#16
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Thread Starter
If you add a conical washer and space the link back out like the factory did you will reduce the stresses greatly!
I don't often quote or refer to Wikipedia, but this quote from this page
http://en.wikipedia.org/wiki/Weissach_axle
is interesting:
The Weissach axle (pronounced 'Vise-' as in 'advise' and '-ach' with guttural 'ch') is a special rear suspension arrangement devised for the Porsche 928. The goal of the Weissach axle was to eliminate lift-throttle oversteer by allowing the rear suspension to adjust itself during cornering maneuvers.
The Weissach axle is a variant of the semi-trailing arm suspension. The tendency of a vehicle to oversteer when decelerating is compounded by the compliant bushings found in most trailing arm suspensions (emphasis mine). When the vehicle is decelerating, the trailing arm pivots towards the rear as the wheel is "pulled" backwards relative to the chassis. This results in toe out, which makes the vehicle unstable.
For the Weissach axle, the front pivot bushing of the trailing arm is replaced by a short link. In this arrangement, when the vehicle decelerates and the wheel is "pulled" back, the result is toe in. This adds to stability and thus, reduces oversteer.
The Weissach axle is a variant of the semi-trailing arm suspension. The tendency of a vehicle to oversteer when decelerating is compounded by the compliant bushings found in most trailing arm suspensions (emphasis mine). When the vehicle is decelerating, the trailing arm pivots towards the rear as the wheel is "pulled" backwards relative to the chassis. This results in toe out, which makes the vehicle unstable.
For the Weissach axle, the front pivot bushing of the trailing arm is replaced by a short link. In this arrangement, when the vehicle decelerates and the wheel is "pulled" back, the result is toe in. This adds to stability and thus, reduces oversteer.
11-22-2013, 12:48 PM
#17
I took the original link and took the conical aluminum piece out of the inner part of the link. I then turned it down and fit a heim joint over it. This allows greater "stiffness" to the camber control on the rear, but still allows the front to rear "turning sweep" of the whole hub assembly.
11-22-2013, 12:51 PM
#18
Developer
Thread Starter
The solid upper links that Mark A and Mike Simard use have spherical rod ends which do not restrict for aft movement. On top of that, both of these gentlemen have their weissach axles pinned.
11-22-2013, 01:06 PM
#19
Developer
Thread Starter
BC - can you share a picture?
How long ago did you make this mod and how many miles /what kind of driving have you done with it?
Has it cracked or broken the link? How are the mounting bolts that Lizard is worried about? Bent?
How long ago did you make this mod and how many miles /what kind of driving have you done with it?
Has it cracked or broken the link? How are the mounting bolts that Lizard is worried about? Bent?
11-22-2013, 01:09 PM
#20
Nordschleife Master
Carl,
Re-read the wiki. In MOST TRAILING ARM.
By reducing the flex that the rubber bushings give in the weissach axle, you reduce the toe in effect giving a greater tendency towards toe out which induces oversteer.......
Re-read the wiki. In MOST TRAILING ARM.
By reducing the flex that the rubber bushings give in the weissach axle, you reduce the toe in effect giving a greater tendency towards toe out which induces oversteer.......
11-22-2013, 01:12 PM
#21
Nordschleife Master
A hiem joint like BC has used will not cause a binding with the for/aft movement as he retained the stock conical standoff. He retained the stock function, and only replaced the rubber with a non compliment part. His modification does not reduce the movement in fact it would lessen the stresses on the part.
11-22-2013, 01:21 PM
#22
Developer
Thread Starter
I prefer not to assume how BC installed his heim joint until I can see his pictures, a drawing, or similar. You are speculating on how he did his mod.
I read that he removed it. But don't know if he incorporated it back into his design or not. Can't tell by his brief description. That's why I have asked him to expound upon it.
...as he retained the stock conical standoff
11-22-2013, 03:43 PM
#23
Nordschleife Master
He has retained the factory conical piece and knowing BC he had properly secured the hiem joint in the banana link.
11-22-2013, 03:53 PM
#24
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Just a laymans input here. I have my rear suspension completely out of the car and when I pull fore and aft on the hub I can see how important it is for this "banana" joint to have some flex/movement in it.
If it is made stiff or not allowed to move all the force will be transmitted in to the bolts that hold it in place.
heres a pic to show you a birds I view.
When "A" moves...you get significant movment in an arc along part "B"...sorry, I think its imperative that this movement be kept as it allows the rear end to "move" as designed.
If it is made stiff or not allowed to move all the force will be transmitted in to the bolts that hold it in place.
heres a pic to show you a birds I view.
When "A" moves...you get significant movment in an arc along part "B"...sorry, I think its imperative that this movement be kept as it allows the rear end to "move" as designed.
11-22-2013, 04:21 PM
#25
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928 331 588 10 - 4 in stock, 12 in USA & 700 in Germany
928 331 588 15 - 6 in stock, 4 in USA & 285 in Germany
928 331 089 04 - 8 in stock, 130 in Germany
928 331 588 15 - 6 in stock, 4 in USA & 285 in Germany
928 331 089 04 - 8 in stock, 130 in Germany
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
11-22-2013, 05:33 PM
#26
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Forgeting entire Weissach movement and what harder bushing can do to it I think setup is dangerous unless extra conical washers are added to take up empty space where conical alu pieces in stock bushings reside. Using heavy duty washer just means it probably takes longer to fail but I think there will be problems. Adding four more conical washers will remove this problem completely.
11-22-2013, 05:36 PM
#27
About 2005. Maybe 50,000 miles (not always driving it, drive other cars for work, travel, etc)
Why would it crack the link? The mounting bolts are the same. I used the original conical faced piece and made sure the heim ID can fit over it. Then spaced it front to back to make sure there is no movement.
I am saying it allows full for aft swing movement. The complexity is the heim rod made it adjustable for camber at the top, and its still adjustable at the bottom, so you can actually induce camber AND change the rear track.
11-22-2013, 05:37 PM
#28
A hiem joint like BC has used will not cause a binding with the for/aft movement as he retained the stock conical standoff. He retained the stock function, and only replaced the rubber with a non compliment part. His modification does not reduce the movement in fact it would lessen the stresses on the part.
Simard made an even better one that can be used on a lowered 928, because mine is straight and I'm always concerned over it hitting the body. His is beautifully machined and made a sort of U shape.
11-22-2013, 05:39 PM
#29
The heim joints are huge. I think I overdid it.
11-22-2013, 07:12 PM
#30
Nordschleife Master
Tony shows what I am referring too with his picture.
Carls design (with or without small conical washers) will prevent for aft movement making it dangerous as the upper link is getting all the stress put on it.
Adding conical washers between the large washer, and crossmember/hub carrier will drastically reduce shear forces on the bolts. But it still will not eliminate the fart this modification prevents for/aft movement.
Carls design (with or without small conical washers) will prevent for aft movement making it dangerous as the upper link is getting all the stress put on it.
Adding conical washers between the large washer, and crossmember/hub carrier will drastically reduce shear forces on the bolts. But it still will not eliminate the fart this modification prevents for/aft movement.