[Shad Laws]

Hello-

Shad, thanks for your response to my questions. Also, thanks for not bashing me for referring to “neoprene” bushings instead of “polyurethane”, hope I didn’t loose all creditability.

Nah. If we all lost credibiliity when we made typos, we'd all be screwed. Me especially :-).

But even though I think they're going to be a real pain to adjust, still don’t understand why the heim joint will not work as well as the spring plate in maintaining toe as long as they are adjusted properly.

It will do fine. I was referring to the suggestion of simply removing the torsion bar and leaving the springplate and rubber bushings in there alone.

The only concern I see with the heim joint setup is the lack of isolation mounting. I do stand to be corrected (there are isolation heim joints), but I don't see any on the setup. This may cause other problems down the road.


I’ve spent a lot of time trying to understand how the various IRS components work in relationship to each other. I’ve assembled my IRS setup and made sure that everything worked smoothly (i.e., there is no binding). One of things that I noticed was that there is very little movement in the inner bushings, even without the outer bushings installed. But maybe enough to make the fine adjustment required to obtain the correct toe.

You are correct: it usually takes some effort to pull/push the trailing arm along the slotted bolt holes, but it is necessary and does allow the fine adjustment of toe. BTDT.


At any rate, that situation has nothing to do with the fact that I’m not using the spring plate. I don’t think the toe will change any more with the up and down movement of the arm than it would with the spring plate, but I guess I'll find out.

That is called bump steer. Bump steer is the change of toe with the change in suspension position. You are correct that the bump steer characteristics won't change much at all with the Eagle setup vs. stock.

With a isolation-mounted, rubber-bushed system (a la all OEM semi-trailing arm rear suspensions), the problem isn't bump steer. The problem is that the mounts are somewhat flexible. So, under high loads, it is possible to change the toe of the suspension due to lateral forces imposed on the suspension system, not so much vertical ones that just change the suspension's position. This effect creates the "classic oversteer" problem of an early 911 on a hard turn when you start decelerating. My point was that removing the torsion bar and leaving the springplate with the bushings left in there as the pivot, this effect would get far worse.

For more info on this, do a google for Porsche 928 Weissach Axle. It should give some diagrams of the semi-trailing arm rear suspension, how they lead to weaknesses, and how the weissach axle suspension system corrects these problems.

The Eagle setup won't have the problem of a grotesquely flexible pivot like removing the torsion bar and leaving the springplate in there would create. Rather, I fear that it *may* (again, I stand to be corrected on this one) have the opposite problem - too rigid, leading to a problem with absorbing shocks (may fatigue parts faster) and a harsh ride. Solid mounts don't do well on street-driven cars...


I have not been able to detect any toe change at this point. It appears that the spring plate must twist as well as bend inward (two seperate motions) in order to abe able to follow the arc of the IRS arm which is pivoting about a different axis.

Yes. This is why the springplate setup has almost no effect on camber... camber is controlled almost exclusively controlled by the trailing arm itself.

The heim joint setup is able to accommodate that same arc because of it allows movment about the pivot point.

Correct.

I don’t disagree at all with your statements about the merits of the torsion bar versus that of a coil-over. One of the reasons that I have opted to go with coil-over was to get additional wheel clearance.

I'm confused - how do the coilovers give more wheel clearance? Do you mean that you are just stiffening the suspension to prevent bottoming out?

Also, I thought the adjustability and availability of different spring rates would be a plus.

Sway-a-way makes a billion different torsion bars (springrates)and 944 arms are easily adjustable. :-). Again, I'm not saying that coilovers don't have other benefits, but if these are the benefits you are looking for, you don't need them.


And, less importantly, I just don’t like torsion bars, no good reason just don’t like them.

Well, okay :-).

I like F^3 - Form Follows Function. When I spend money and perform a modification, I like to know that a performance gain will result. If you're going to do the coilover modification, then take advantage of what else it can give you! Make it not only look cooler than when you started, but perform better as well!

Take care,