lower control arm 1972 Duster
So when was the last time you EVER heard of an OEM mopar LCA failing by popped rivets of the literally millions out there for over 6 decades of use?
Why is nobody marketing LCA high strength bolts as a weakest link rivet upgrade?
You haven't because the test loads are never achieved under ANY driving conditions that we here face.
Now this is moving the goal posts. It doesn't matter that you've never heard of the rivets failing, they are in fact the most obvious failure point for the factory LCA. And it shouldn't be surprising to you that in a destructive test that the rivets failed first. Where else would the factory LCA fail? You think it will buckle before the rivets fail? Nah. Maybe the cast section that's riveted in, but it would be between that and the rivets. So it makes perfect sense.
I have in fact heard of the rivets failing, although the cases I know of were accidents so it's not of great importance. Still, we were discussing slop weren't we? Not strength? Goal posts
moved.
The reason being the real world loads are mostly limited by a torsion bar rated in the 200lbs/in and travel can't exceed approx 5 in with a preload of less than 1000lbs, hitting wheel destroying potholes or banked concrete retaining walls excluded. IF the LCA is flexing, and as agreed to earlier they ALL do, upping the TB rate ever so slightly completely offsets that minute flex.
First, factory torsion bar loads were in the 90-120 lb/in range. Second, 300+ lb/in bars have become pretty common for pro-touring style cars with large and sticky front tires. I run 300 lb/in bars. Third, the load is not limited by the torsion bar, because if the suspension bottoms out the load can be MUCH higher. And pot holes can pretty easily bottom the suspension. Even mine, with 300 lb/in bars. On a street car it's a bad assumption to think the highest load will be the total applied by the torsion bar.
Finally, increasing the torsion bar rate will not "offset" the flex or slop in the LCA. It will in fact
increase it, because the load on the LCA can be higher. Better tires put more force into the suspension, larger torsion bars resist that, and the LCA's in the middle.
I am skeptical of the CAP reported test results above anyway, as to what the complete test conditions were or if the test was skewed to achieve the results reported.
The test was conducted by Richard Ehrenberg at Mopar Action. The LCA's were put in a 10 ton press, supported at the pivot points, and placed under load until they failed. They have 2 major loading locations (excluding the struts and sway bar), and a 2 point destructive test is ridiculously simple. I don't agree with Ehrenberg on a lot of things, but even he shouldn't screw up a 2 point destructive test being an SAE guy.
Do you have any test results to show otherwise? I bet not.
I have not seen the QA1/OEM LCA side by side. I have QA1 at PRI and in press releases. I find the claim unsupported and likely misleading and inconsequential anyway as to the "flexing" concern. My initial impression at PRI was how frail compared to OEM they might be but couldn't decide why they were not up to the task.
I completely disagree the LCA TB pivot points is to suppose the prevent LCA movement F to R, that is the sole task of the strut. If it was the LCA bolted single shear pivot point is a very poor engineering design with now even more tasks.
Well, I have seen the QA1 and OEM LCA's side by side. For that matter, I've seen the later 73+ B body LCA's next to the A-body LCA's too, and I wouldn't put money on the A-body LCA's against either of the other two.
Ehrenberg agreed that the QA1 LCA's "look kinda spindly" (his words!) but the DOM tubing they're constructed of is tougher stuff than the factory LCA's. Either way, basing your opinion on what things look like vs. how they actually hold up in a destructive test is wrongheaded. You asked for evidence, I supplied it. You don't like it, come up with your own evidence. And still, this isn't the slop discussion, you're just wrong about the quip you threw in about the QA1 LCA's. If anything, they're stronger than the CAP version, QA1 has improved the design. I've have the CAP version too, so, I've compared those as well.
You note "small" in your ball joint movement concerns. You fail to quantify that. When you do you might want to mention how relative that movement is to those running say 40 aspect and up sidewalls. Not sure what OEM "slop" camber reduction method has been shared here anyway short of aftermarket replacement.
The lack of concern of conflicting arcs you voice, albeit minor, is mainly because the dreaded "slop" allows it.
Well, how much slop is in the LCA's in the video? An 1/8"? More? That's small, but it's not insignificant when you're talking about caster change. Or toe change, if the LCA's move forward the toe angle changes too.
Comparing that slop amount to the deflection of the tires is a false comparison too. You get both of them, not one or the other, and they add up. You can eliminate the slop from the LCA, you can't do much about the tire deflection other than running better tires.
Removing the slop is easy, if you watch Jim's video. You can eliminate ALL of the slop at the socket end of the LCA with a plate and a strap.
The arcs of the strut rod and LCA are not "conflicting", they're diverging. That's an important distinction. And no, the "slop" does nothing for the diverging arcs of the LCA's and strut rods on my car. As I've already mentioned, I run QA1 LCA's that have no slop like the factory LCA's, as well as delrin LCA bushings, and adjustable strut rods (heims, no bushings). So, no slop, still diverging arcs, and I've tuned the length of the strut rods and checked for binding throughout the suspension travel range on my car. There is no binding in the range of travel, which is why I don't worry about the diverging arcs. They overlap well enough so there isn't binding in the range of travel I use (~5").
The Kit cars were designed to reduce owner maintenance costs and improve reliability on Sat night wheel to wheel grudge rubbing and racing. That hardly applies to our uses.
Says you. They had to handle well and hold up to much higher loads than most street cars, plus deal with "rubbing is racing". They also used much larger torsion bars and better tires, so, their construction and durability would be well used on a pro-touring car with better tires and larger torsion bars.
The later B LCA pictured IMO seems to be actually a weaker design than the earlier design and its main success from a corporate standpoint, it was an easier/cheaper item to mass produce in quantity with a lot less parts and labor, and any "dreaded" slop reduction was simply a byproduct of the process. I may be wrong. You are welcome to prove me wrong.
However, since this newer design is fundamentally loaded much different than the older version, it really should not be included in this discussion.
Seems to be? You haven't seen them in person either have you? They're heavier than the A-body LCA's. And they lack the rivets, which are the strength limiting factory on the A-body design. And they don't have the cast section to support the ball joint, which can also fracture. Sorry, the later B-body LCA's are tougher stuff.
As for loaded differently, no, they aren't. They're loaded at the ball joint, the torsion bar pivot, the strut rod, and the sway bar, EXACTLY like the A-body LCA's.
Still nobody has yet quantified the downsides of the dreaded "slop" in real world use. IMO, you and others have drank the marketing koolaid on a problem, that in realty has not yet been proven to or may not exist.
Marketing cool aid? Ok. The QA1 LCA's are lighter than stockers, by about 8 lbs. Less unsprung weight. They also increase the suspension travel, because their height profile is lower. That's why I run them, lowered the car without losing suspension travel. Their construction that eliminates the slop between the LCA and the pivot is a nice bonus. I didn't care that they were stronger, but, yeah, they are.
Why don't you show that the slop between the torsion bar socket/pivot and LCA at the K frame end
isn't translated directly into slop in the path of the ball joint? Because movement at the ball joint end of the LCA will result in irregular changes in caster, camber, and toe. All of which can result in poor handling, especially if they're not consistent changes. And since the ball joint is at one end, and the pivot is at the other, it seems pretty logical that a bunch of slop between the torsion bar socket/pivot would translate directly into slop in the path of the ball joint.
