Rear Tubular Control Arms

[Sebnuts]

ZZP had tubular control arms for the Cobalt at one point (have been sold out for ever it seems), but never for the LNF anyway.
My bushings are shot and I wanted a bit of an upgrade from stock so I designed some up in CAD.
The heim joints are all 3/4". The horizontal one uses an aftermarket style 3/4" mount bar with 2" mounting width, 3/4" ID misalignment spacers. The rear has 2" mounting width by 9/16"ID misalignment spacers.
Ball joint is a 3/4" FK spherical bearing with a custom turned pin and 5/8"ID misalignment spacers.
Tubing is all 1.25x.120 wall.

Looking for some feedback on any possible issues I may have missed or areas for improvement before I started ordering hardware.
Images shown with stock control arm overlaid.

 

[Gtstorey]

Probably not worth the effort since OTTP now has replacement ball joints. Maybe if you can fab/machine it up yourself might be interesting but I would not expect it to perform better than stock arms with the available improved bushings at the subframe ends. You will have more range of camber adjustment though.

Have you compared the weight between the design and stock?

 

[Sebnuts]

I plan to fab/machine myself, it's a pretty simple/low effort setup. As far as adjustment goes, I'm more interested in adding anti-squat by dropping the leading arm to the bottom side of the cradle, and changing roll center height by adjusting the ball joint pin/spacer lengths if needed.

I have not compared weight or strength yet, but it is on my list of things to do.

 

[Desert Sasqwatch]

Nice design, simple and has some adjustability. Keep in mind the stock subframe is designed for a FWD application, so has inherent (minor) anti-dive built in - the subframe rail is angled downward and the front of the stock LCA is lower than the rear. This is the opposite of what is needed for anti-squat in the rear suspension. The LCA needs to be angled upward at the front mounting point, not down. There are several websites that go in-depth for anti-squat geometry to define how to set it up properly. Make certain you find one which illustrates a strut suspension.

 

[Gtstorey]

Is the "dimple" for the front mounting point deep enough for the heim joint?

 

[Desert Sasqwatch]

Yes, I measured it a couple years ago when I was looking to do what is being proposed by Scott. The crossbar mount can be shimed outward if needed.

 

[Sebnuts]

The OD on the heim is actually smaller than the OD of the bushing housing on the factory arm.

Squatch, my terminology was wrong. Most of the examples on the internet have a trailing link (in front of the axle). Like you said, the LCA needs to be angled upward, and with a trailing link, you raise the forward mounting point.
I said I was dropping the trailing arm down, I should have said I was dropping the rear most heim if the leading link down. This will result in an upward angle of the LCA.

 

[Desert Sasqwatch]

Yes, the anti-squat needs the front IC rotational axis lines 'pinched' (versus the rear 'pinch' in the front suspension anti-dive). I see the high-angle spacers illustrated for the rear mount in your CAD photos. Will you be able to drop this LCA mount enough? With 2 3/16 spacing between the subframe flanges at the rear mount, will be a challenge to space/shim the heim/HA spacers to lower the LCA rear mount. You may need to get creative with the front mount crossbar to offset the bolt-thru holes it to raise the forward mount of the LCA. This is all stuff I've looked at previously and am trying to offer up the ideas I thought through when I had the notion to create new LCAs.

 

[Sebnuts]

To get enough angle (9-10°) may require mounting the rear below the cradle. Without modification, this would create a single shear joint, which is not ideal and may or may not be strong enough, I won't know for sure until I do the stress analysis.
There are a lot of unknowns still as I don't have the kit yet and don't know where the upper strut mount is located.

 

[Gtstorey]

I would not place anything below the cradle, just seems like to much a chance of hitting something, unless track only vehicle.

 

[Desert Sasqwatch]

Please note the stock Cobalt LCAs have a 2(?) degree forward cant. The strut mounts are 90 degrees vertical from this point (side view). The uprights are installed with no caster. This should help you visualize the upper part of the suspension geometry. BTW, if you don't have your kit where did you get the CAD for the frame and subframe? I've been looking/asking for this for a couple years.

 

[Sebnuts]

I 3D scanned the subframe, control arm, upright, bearing hub and wheel/tire from my donor yesterday. I got the frame model from Ross here on the forums. I believe this is the first iteration of the frame and accuracy to the current version is not correct (it's obvious that the forward subframe mounts are not correct in the model) but it's a good place holder until I get my frame, at which point I will update it.

 

[comegetjoe]

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