This is also true of most of the aftermarket control arms. We just assume they are all welded correctly using the proper materials. All we can do is look at the track record of them and decide if one or another gives you the most piece of mind. Personally, I prefer unmolested factory parts that have been tried and true for ages.
We assume the factory did its due diligence as well, and yet there are many cases (TSB's, recalls) where we know the factory fell short too. And that was before all those parts were 50 years old, and we consider that nothing made 50 years ago is as strong as it was the day it was made. Heck some of the stuff that's sat unused on a shelf for the last 50 years isn't as strong as when it was produced. Be educated and informed, but at some point you just have to hit the street.
The upper control arms don't support the weight of the car like the LCA's do, the load requirements for them are quite a bit lower. Yes, their failure could still be catastrophic, but the margin for error as far as strength goes is MUCH different than even the LCA's.
yeah, for it to have fatigue strength anywhere near the parent material, the weld itself would have to essentially be ground and polished to the point of being basically indetectable through the paint. a plain old class C unground fully penetrated fillet weld will have a fatigue life of maybe 10-20% of the parent material.
Sorry, but if we're going to be technical even if they have a fatigue strength that's only 10% of the parent material that's only a single order of magnitude, not "orders of magnitude".
And I agree, if the strength is truly only 10% of the parent material that's
not good. But that would be a pretty extreme case, and I think the fact that the UCA's in question have been used on the street for at least 2 years would demonstrate a fatigue strength that's substantially better than 10%.
"Orders of magnitude" would mean that the welds would have to be
hundreds of times weaker, at minimum. For example, Rick Ehrenberg tested factory LCA's in failure in the April 2011 Mopar Action. He did a two point test (supporting the LCA at the ball joint and pivot) and used a press to add pressure until the LCA's failed. The stock LCA failed at 2,800 psi. Now, an order of magnitude would mean a failure at only hundreds of psi. And "orders of magnitude" would require a failure in the
tens of psi. The factory UCA's wouldn't take as much force before they bent, the LCA's are far stronger. But even if you assumed the fatigue strength of the UCA's is in the thousands of pounds, that would mean the fatigue strength would have to be in the tens of pounds to be literally "orders of magnitude" lower. That wouldn't hold up on the street for any length of time.
So yes, that's being pretty technical. But so is using the term "orders of magnitude" correctly, and it is a technical term.
