[Shad Laws]

Hello-

Shad, I’m curious about your comment that the one of the spring plate's function is to maintain toe. I’m not sure exactly what you meant by that. It appears to me that the adjustment for toe is through the placement of the washers on the inner pivot bolt.

Changing the washers is a _major_ adjustment. Often times, it never needs to be done. Minor adjustments, like +/- 1/8" of toe, are done by moving the trailing arm bolts in the slotted holes of the springplates.


Also, unless you have a lot of slop in the inner bushings, you can’t substantially change toe by adjustment of the spring plate. It seems to me that you adjust the spring plate to accommodate the position of the suspension arm based on the placement of the aforementioned washers.

No. Basically, the correct procedure is to measure the toe you have, then decide whether a major (and coarse) adjustment is necessary by washer moving, and then do a minor (and fine) adjustment by moving the bolts in the slotted holes.

Even 1/16" of toe difference can make a big change in the way the car handles.


The spring plate would then help support the arm and prevent a change in toe due to wear in the inner bushings. Is that what you meant?

No matter how you cut it, the rear suspension is held in place by two pivot points of rubber. It is therefore flexible (which is why you can move it in the slotted bolt holes).

Toe is not a constant thing. We like to think of it that way - we measure it with the car on the ground and it stays, right? I wish :-). The truth is that during use, the rear suspension undergoes many different forces in different directs under different conditions, and the rubber bushings flex. That's why it's a benefit to use polyurethane bushings... a little more rigidity for better toe control.

The torsion bar helps keep the springplate in place, too. It takes some force to "bend" the outer ends out of place and change the toe. This is good - it increases the rigidity of this pivot point compared to the rubber alone.

By contrast, the inner trailing arm bushings are much smaller - there's a lot less flexible rubber there. This is because there's no torsion-bar-ish-thing there to contribute to rigidity, so they made the rubber pieces' geometry more rigid to start with.

Long story short: I wouldn't simply remove the torsion bars and call the conversion "done." If you don't put something back there, handling will suffer.

Germanlook - form follows function, right? I know the form of no torsion bars seems cool, but the function doesn't follow. Unless, of course, you do something else to compensate.

I’d be concerned that if you try to adjust toe with the spring plates, you could put the arm in a bind that could cause premature wear of the bushings or worse. Does this make sense?

I understand what you are saying, but it's wrong. The washers alone don't allow a fine-enough toe adjustment.

Bottom line, I think the Eagle Products’ conversion will work just fine if adjusted properly.

One concern I have about their system is that there doesn't appear to be any isolation mounting. While this makes for a ton of rigidity, I do wonder if this is ultimately problematic... no "shock absorbers" and perhaps a much harsher ride. <shrug>

Also, I think Ricola explained very well why just relaxing the torsion bars does not work. That is unless of course, you’re looking for a very very stiff rear suspension.

Well, hang on... we have to back up and ask why the heck we want coilovers in the first place.

If the answer is to look cool, then nothing I said applies. Form doesn't follow function, so the book is open on what you want to do :-).

But, I'm assuming that it isn't. Okay, so before we go changing what we have, we should ask this: what's wrong with the stock torsion bar system? The stock torsion bar system provides a constant linear spring rate. Now, we may desire to change this for three reasons:
- make a higher linear spring rate. This can be accomplished with stiffer torsion bars - very simple, staightforward, lightweight, and cheap (<$200 for everything). IMHO, adding coilovers for this purpose is a waste of money, time, space, and weight. Not to mention that you are imposing new stresses where the system was designed to take them... while these problems are curable, why cure them if they don't provide a net benefit?
- make a progressive spring rate. This is a good thing to do! There are two ways to introduce a progressive spring rate. The first is pneumatically - gas-filled shocks. We can do this with torsion bars, too. Many of the cheaper coilover setups use only this method, and therefore, changing our system to use this is pretty much a waste if this is our only goal. The second way is with special progressive springs. These kick ***. Here, the spring itself looks different from top to bottom - part of it is wound more tightly than the rest. These are a good reason to add coilovers! Or, simply reduce the torsion bar's springing by a bunch and make up for it with these springs (i.e. relax the torsion bars and add the coilovers). Unfortunately, these aren't cheap... <sigh>
- add adjustability. While one could argue that the stock torsion bar system is adjustable, it's a pain in the ***. If this is your only goal, consider 944 springplates. They are lightweight, relatively cheap (junkyard items), and work well. Of course, adding coilovers accomplishes this, too. But, they also add weight. But, they also "look cool." Ah, well.

Take care,