It doesn't matter what they built, I mean it's a metal stamping with some welding, they could literally have sent it to anyone who can meet quality standards. Honestly even those weren't very high, I agree on that. The general design of it is quite good though, especially considering using a slide rule and what else was out there that had existed before. It's clear they actually understood engineering principles.
The entire car is made with spot welds of varying quality. I can't remember ever seeing a picture of an OEM K-frame with popped spot welds. The welds at the pivot pin tubes, sure. The 3D shape in the vertical direction and the k shape in the horizontal direction is where the strength comes from but the stamping is basically free of ribs or darts otherwise. The brackets are somewhere between Billy Bob with a stick welder and Ray Charles welding it with his feet yet plenty of them are out there, I don't think the failure percentage is that high.
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I've had this discussion with you before. I know you're going to say for crash impacts, yes it would help stiffen the part near the firewall that helps with crash which also means the front structure between the driver and the front suspension is stiffer. Which is postive for handling. You even see tying the firewall to the inner fenders / shock towers on things as early 1960 Falcons to the strut towers before there was even FMVSS or they cared at all about crashworthiness.
I adapted the braces to my own car and yes you can feel the difference, it's minor but there. Maybe you can't tell with stock 85 lb/in wheel rates but at 252 lb/in yes.
We have seen the spot welds actually pop between the firewall and the inner fenders with high spring rates. That area of the car flexes a lot because of no surprise to anyone who knows engineering having things at generally right angles isn't very stiff on its own and this triangulates the firewall to the inner fenders. This is preventing parallelagramming to some extent. They're strong enough you can shake the car back and forth and flex the suspension with them. You see a variation of this type of brace on basically everything once there was any care at all about chassis stiffness. The car companies are borderline fanatical about stiffening this exact area of the car in the same way now for better performance and NVH. And usually they're also called k-braces. I'm seeing a pattern here. Almost all newer BMWs, 2024 Mustang, and even the 2020+ explorer have similar braces. Our cars are made out of fairly light gauge sheet metal, they need all the help they can get for stiffness. The frame rails themselves are even quite light weight. It's not comparable to a modern fully boxed truck frame which may have similar cross section.
