Leaf spring slider mounts and composite springs - comments, advice?

[70vert]

Hey all,
In my eternal quest for a great-performing but cheap(ish) rear suspension solution, I'm looking at Flex-a-Form springs and the Cobra Automotive-style slider mounts on p. 7: (WARNING! 1.2mb catalog download!)

http://cobraautomotive.com/cobra_cat.pdf

Also, it seems like a cheaper, possibly identical, mount can be had right here:

http://www.speedwaymotors.com/xq/aspx/display_id.2151/qx/product.htm

Questions are:

1. How exactly do these work?
2. Cobra Automotive says these can only be used with their road race springs - is that because the springs are narrower or wider at the eye?
3. Related to above - can these be used with the Flex-a-Forms?

My basic plan right now is to start with the Flex-a-Forms and these mounts right now, and if I find I need a Watts Link add the upcoming one from Evolution Motorsports. I'll add traction control way later when I replace the engine . . .
Any advice, comments, etc., would be appreciated, ESP. from someone who already owns the slider mounts! :SNSign:

 

[Hack]

Bump..
I think rear sliders are a terrific idea. Anyone out there with them?

 

[70vert]

thanks for the bump

Bump..
I think rear sliders are a terrific idea. Anyone out there with them?

hack, thanks for the bump. I still am not quite sure I understand the theory. Do they mount vertically like the shackles, or horizontally and the eye slides back and forth.

I think I understand that during certain parts of the leaf's travel, you're going to get binding, or at least a heavily increased spring rate, because the "bow" shape of the spring simply cannot move out horizontally, all it can do is to distort the shape of the "bow". The sliders would allow the "bow" to move out horizontally, right?

 

[66bluepony]

Springs

Go for the composite springs first. You probably wan't need anything else.

 

[70vert]

Figuring on new shackles anyway

yeah, I'm not going to mess with the Watt's or any traction or anti-brake-hop device until I see how the FAF springs work, but I was figuring on having to replace the shackles and that I might as well look into the slider mounts if I'm going to do that.

Go for the composite springs first. You probably wan't need anything else.

 

[Hack]

hack, thanks for the bump. I still am not quite sure I understand the theory. Do they mount vertically like the shackles, or horizontally and the eye slides back and forth.

I think I understand that during certain parts of the leaf's travel, you're going to get binding, or at least a heavily increased spring rate, because the "bow" shape of the spring simply cannot move out horizontally, all it can do is to distort the shape of the "bow". The sliders would allow the "bow" to move out horizontally, right?

The way I've seen sliders mounted, they are set up so that the rear eye of the spring can move toward the front or rear of the car only.

I don't know what the exact effect would be, but I have no shortage of guesses! I don't like bushings, because I think they tend to bind and in general behave in an unpredictable manner. They also allow movement in every direction, not just the required directions. So a shackle would allow the rear end to shift side to side, as well as binding as you described.

One nice thing about a rubber bushing is vibration isolation. The ride of the car might be noticeably more harsh with a slider in comparison to a shackle. However, I wouldn't be certain of this after learning of the effect of putting a roller bearing in the spring perch.

 

[C0V3R]

HMmm... roller bearing sliders could make for a very smooth ride potentially... Does anyone have pics of such a setup?

 

[70vert]

that's what I thought, thanks

The way I've seen sliders mounted, they are set up so that the rear eye of the spring can move toward the front or rear of the car only.

That's what I figured, thanks. When I said "horizontally" in reference to the spring, I meant that the spring eyes could get farther away or closer to each other, but the middle, the "bow" would move vertically, sorry if it wasn't more clear.

The weird thing is, these things are mounted on plastic pucks that slide back and forth - does that mean they just slide around and slam against their stops as the suspension moves? Seems unstable to me, but if they are being raced there must be something I'm not understanding. Dug up a pic:

AHA! I found a great explanation of the negative handling effects of shackles, and how a slider counteracts that:

http://www.bedfordspeedway.com/toolbox_leaf.htm

Still don't understand what keeps the slider from slamming back and forth, unless it's just the natural tendency of the spring to keep its' original shape.

I don't know what the exact effect would be, but I have no shortage of guesses! I don't like bushings, because I think they tend to bind and in general behave in an unpredictable manner. They also allow movement in every direction, not just the required directions. So a shackle would allow the rear end to shift side to side, as well as binding as you described.

yeah, the link provides a better explanation of what shackles do. The front spring eye bushing is another thing - there's a thread on Corner Carvers where they explain that, basically, in, say, a left hand turn, the body roll and sway basically wants to lift up the inner wheel because the springs will resist twisting and pull up that side of the axle. Hard bushings will make the effect happen sooner, which may make the effect more predictable but would reduce your overall traction. This slider mount and a hard bushing up front would seem to do the same thing. As well as make the ride harsher like you mentioned.

It would seem like those leaf springs twisting and pulling up on the inboard wheel in a turn would do the opposite of an anti-sway bar - so do you get an anti-sway bar to counteract it? Cobra Automotive certainly doesn't . . .

ARGH! Too many variables! Makes you want to convert the rear to something expensive involving coilovers.

 

[69gmachine]

Hello,

They weld to the frame in place of the rear shackles, allowing the rear leafs to slide fore and aft. You need to install them on the springs and then let the weight of the car down on the springs in order to locate the sliders properly. You need to leave approx 1/3 of the travel towards the front of the car (extension), and the other 2/3 of travel to the rear (compression). The stock springs will work, but they force the slider way to the back. I mounted mine as far back as I could without making serious mods to the uni-body. They ended up roughly at the mid-point. Ideally you would want the spring to bottom out before it hits the end of travel, or you're going to hit bottom like a rock, or even worse, rip them out.

Unfortunately, I can't comment on real world driving as I'm still sorting out the brakes and engine on my car. As you've seen from other replies, the main advantage is a linear spring rate, making the rear more predictable. It will also stiffen up the sideward motion somewhat, but it's no replacement for a panhard bar or watts link.

You can custom order springs from Flexi-Flyer, so you might consider ordering them about 1" shorter from the rear housing locating pin to the rear bushing centerline. They're custom parts you can't return, so mock it up and take measurements before ordering.

I'm dying to actually drive my car, but it's been fighting me every step of the way. As soon as I get some drive time I'll let you know. Before I take it to the track I plan to install a panhard rod.

As you noted, you can get them from several vendors for much less than what Cobra Automotive is asking.