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Originally posted by 36ASedan
Guys, first of all, thanks for all the valueable info.

Ok, here's the short version of where I am at right now:
Last season, I had help with designing the geometry of a third link setup. I have everything installed on the car as far as the body side goes and have been stuck on fabricating the pickup point on the rearend. I found a 1/4" steel fabbed rear cover (Dana 44) and have fabricated a mount/pickup point which is welded to it (integral part of the cover). I hesitated using it last year because I was afraid of the the stress it would put on the cover studs since they are only 5/16" and there is only 9 or 10 of them (can't recall now). I am currently working on a brace that will at least make me more comfortable with trying the third link out.

Anyway, here is a drawing of how the geometry will end up when fhinished (the seemingly randomly place planes are bodywork and such that cannot be passed through):



This is what I'll end up with if and when I get this 3rd link installed. Thoughts?

-Jeff *]

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This is a continuation of discussion so we can stay off of Eds Wilwood post that we hijacked.
https://www.thirdgen.org/techbb2/new...postid=2681225

In reference to the 3rd link setup 36ASedan is designing-
In response, It is somewhat just like the Ford Mustang 3rd link from what it appears. I am assuming you are still using the panhard to locate the axle? or is the 3rd link going to be an a-frame locator for the axle laterally?

The first thing right off the bat that I do not like is the different length arms used between the LCA's and the 3rd link. They are different arch swings so the pinion changes radically on large travel. This is the same problem the Mustang suffers from performance wise and why they go to an aftermarket TQarm assembly for better results. Pinion rotation for and aft can cause lateral loss of traction in a corner when hitting road imperfections.

 

I have something up my drafting table that I would love to someday tinker with that involves leaving the Tqarm setup, but changing the panhard rod for a more laterally stable Mumford link under suspension travel. This also serves as a chassis brace for the rear boxing and supprting the chassis under the fuel tank and giving a more percise andfreely adjustable rear roll center and geometry angles through susension travel. This is a semi finished idea but the mount points would have to be measured and perfected for a good adjustment range.


This would allow for 1) rear coilovers, and 2) the ability to mount a torsion rear swaybar to the underside of this brace with the swaybar arms leading to the axle (for less unsprung weight) instead of the heavy current design of the swaybar body hanging from the axle.

 

Dean,
First, thanks for moving this.

I would not be allowed to use something like that since it braces or strengthens the chassis - not allowed by rules.

In regards to the Jeg's mount you showed in your previous message: does this just simlply lower the pickup point for the panhard on the axle? Is the panhard still using the stock mount on the other end? If I were to go to the 3rd link setup, would it still be a good idea to lower the roll center also? The rules would allow me to add the Jeg's bracket but the longer ball joints you mentioned for the front would not be allowed.

Again, thanks for all the great information. It really is appreciated. Most (not all) fellow racers would NEVER give it information like this .

-Jeff

 

Jeff,

If the rules allow you to lower the panhard, it might not be a bad move. When you do this, it will change the roll rate of the rear, it will require stiffer rear springs or sway bar (or both), and with that, more rebound damping. The further down the roll center goes, the more leverage the CG has to cause body roll. To correct this, you need to up the roll resistance.

A three link might still suffer from brake hop, it might not. It will depend on how the geometry is set. The effective SVSA length (basicly distance from the centerline of the axle to the IC) and the height. The advantage of the three link is the tunability of where the IC is located, since the angle of the third link determines the IC location, couple with the angle of the LCA's.

Dean, the mumford link is awsome, and easier to package than a watts link. If you ever do make one, make sure you make two of them.

 

I followed this thread over here from the brake thread. This is some really great suspension talk.

I agree with the points made on the braking. Light me up if I am wrong, but I think some of the confusion in the last thread was due to terminology.

I agree BC that lowering the rear will have the effect that was illustrated in the last post. I think the confusing part (at least for me) is that when I think of roll center I am picturing a different plane (side to side). When looking at your picture I would tend to call the points connected, the front and rear Instant Center. With the line being the path of longitudinal load transfer.