lower control arm 1972 Duster
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.
You brought up the rivets failing in a test first as an example of something, not me
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.
I picked 200 as an average everyone could relate to. If we are designing for pot holes as a necessity, address failed rims and low aspect tires in your first concerns not LCA.
Finally, increasing the torsion bar rate will not "offset" the flex or slop in the LCA.
First, I don't accept your premise the LCA is flexing in the first place and you have yet to make the case it is or proved it, This discussion is becoming silly and redundant, and yes it will, as any greater forces in the LCA pivot will tend to keep any slop pinpointed by up to the least force applied (preload when tire is off the ground)
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.
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.
Dude, everything fails, Everyone knows that, Big deal, Show me real world failures first.
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.
Cross section trumps material here all day long. Maybe I should be having this discussion with Ehrenberg?
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.
Well, how much slop is in the LCA's in the video? An 1/8"? More?
So what axis the slop is found is pertinent here. You don't seem to ever address this. Radially or longitude?
axis the slop hereT hat'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.
You mixing issues here. Pay attention. the LCA movement F/R that effects toe controlled by the strut, not the LCA Pivot point, There must be slop to prevent bind from conflicting arcs, The LCA pivot point on a single shear pivot is not designed or intended to prevent F/R angles changes of the LCA. Its movement to any measurable degree is the control of the strut design, not the pivot point slop. Why am I repeating myself here?
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.
Because normally problems are solved first by addressing the lowest hanging fruit, and concern about a .5Deg(?) of caster change is very little bang for buck in the big pictyure even if it is accumulative.
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.
Explain the distinction here that matters, regardless, bind is still the result to be avoided.
And no, the "slop" does nothing for the diverging arcs of the LCA's and strut rods on my car.
Yes it does.
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").
Antidotally, slop is why you have no bind, discovered because there is no moving part of any amount that does not have "slop"
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.
Seems to be? You haven't seen them in person either have you?
Sorry pro touring is no Sat Night "rubbing is racing" or even close.
Ypou state the below newer mopar LCA are "heavier" and stronger "unsprung weight concerns tossed aside and all?
Doesn't matter, its a rather different design ans shopuld not be included here.
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.
A paper tiger argument, in that they don't fail in real world use, and as it seems they are the weak link in the design, the rest of the LCA assembly is as robust as needed evidently.
And they don't have the cast section to support the ball joint,
Are you certain they are cast vs forged? Regardless, ever seen/heard of one "fracturing"?
which can also fracture. Sorry, the later B-body LCA's are tougher stuff.
More empty claims.
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.
To be clear we are not talking about the later B LCA as in 73 up?, The pictured stamped LCA I would be hard pressed to believe it has greater strength that the slop LCA in the original conversation.
I will only agree to at this time that the stamped LCA pictured is much cheaper to manufacture.
Marketing cool aid? Ok. The QA1 LCA's are lighter than stockers, by about 8 lbs.
And you maintain they are far stronger? LOL You are really reaching now.
When did that enter the picture?
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?
I never said I could and I can't. But I can make the case, it's rare, its insignificant, and not pertinent in any application our cars will encounter.
If this is just an exercise in feel good, count me out.
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,
And where your beliefs are different than mine. Quantify the changes of caster, camber, and toe and under what conditions, that concern you and we will continue the discussion.
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.
Based on the actual results of the "slop" and your definition of "directly" and "consistent", this is the crux of our disagreement, skipping all the intermediate marketing koolaid in the middle.
