Subframe Connectors and unibodies

[torredcuda]

Has anyone actually seen factory spot welds fail? Got o any junk yard and look at the wrecks, new or old, and see if any broke apart at the spot welds. I saw many heavily crashed cars as an auto body tech and saw very few spot welds that were broken, usually the metal is torn apart before spot welds break.

 

[torredcuda]

I also worked in precision sheet metal shops for 30+ years and did plenty of spot welding. A spot weld test would be performed to check them and a good spot weld would pull a hole in one of the pieces of metal before the two pieces coming apart. good spot weld is usually actually stronger than the metal around it.

 

[j-c-c-62]

I think just adding torque boxes might transfer the flex to a different area of the unibody as it will still be allowed to flex without the SFCs installed; installing SFCs, no matter what type, ties in the front and rear floor pan/frame rails/suspension points so REDUCES overall chassis flex which IMO reduces stress on any spot welds anywhere on the unibody, same goes for roll cages. Less flex = less stress on welds.

What your logic here overlooks is the overall forces/stress on the chassis does not change. All you have accomplished is moved/concentrated those forces to a smaller area, and therefore the remaining location sees higher forces. Maybe envisioning a typical beam style torsion bar wrench might help, the entire beam bends when torquing a fastener. One could reinforce/thicken the beam midspan, and the entire torque wrench would bend less, but the forces on the entire torsion bar would be the same on the same fastener, but the ends would see higher stress because their thickness/cross sectional area would remain the same. This is the classic stress riser condition we are discussing here.

Also, it is seldom clarified, "torque boxes" have little to do with engine torque. The term refers to the forces the cantilever caused moment effects that act on the chassis rocker sills, which are "torqued"/twisted when the chassis is loaded, by any means, and torque boxes are intended to facilitate/improve/stiffen that cantilever load path.

 

[j-c-c-62]

I also worked in precision sheet metal shops for 30+ years and did plenty of spot welding. A spot weld test would be performed to check them and a good spot weld would pull a hole in one of the pieces of metal before the two pieces coming apart. good spot weld is usually actually stronger than the metal around it.

Main point is, a spot weld is seldom stronger if ever than a not welded section or a continuous welded section, and failure normally occurs at the weakest point, whatever that is. Additionally spot welds somewhat mimic rivet failures, when one goes, the adjoining ones incrementally become overloaded until total failure, or the item is as strong as its weakest/poorest connection.

Our aftermarket SFC's eliminate the cantilever moment design almost entirely and don't need to deal with twist forces directly, and why tube style SFC offers little if any advantage in this stiffening goal.

 

[68 Sport Satellite]

Boxed equals strength. I did none of the labor.

View attachment 1789512

based on photos, Dennis' gets my photo for cleanest look. His car drives and handles amazing.

 

[icetech]

I did cartool also.. did it myself, so it could be better Can report.. car has not ripped itself apart yet..

 

[torredcuda]

Main point is, a spot weld is seldom stronger if ever than a not welded section or a continuous welded section, and failure normally occurs at the weakest point, whatever that is. Additionally spot welds somewhat mimic rivet failures, when one goes, the adjoining ones incrementally become overloaded until total failure, or the item is as strong as its weakest/poorest connection.

Our aftermarket SFC's eliminate the cantilever moment design almost entirely and don't need to deal with twist forces directly, and why tube style SFC offers little if any advantage in this stiffening goal.

"The test highlights that if performed correctly a spotweld is, in fact, stronger than a MIG weld in THLE steel at a thickness of 2.5mm" Whats Stronger a Spot Weld or a MAG Weld On THLE Steels?

Of course it will vary by material, application, production and many other things and they can fail just like like anything. Again - I`ve seen many crashed, rolled, mangled vehicles and it`s very rare they rip or break apart right at the spot welds. I do think ANY bracing, plates, tubes etc. added to a unibody, even bolt in ones, will help stiffen it and create an overall stronger chassis.

 

[j-c-c-62]

"I do think ANY bracing, plates, tubes etc. added to a unibody, even bolt in ones, will help stiffen it and create an overall stronger chassis."

So would a heavy coat of paint I suspect. That was not really the question, unless what are you willing to settle for is any incremental improvement at all vs what the best or most efficient solution is to achieve the intended goal. Leaving anything on the table is not normally my style.

We can argue weld solutions all day long, spot welds can also be very close in effectiveness to proper plug welds. The test linked is using steel alloys not used in our era of cars and makes the test informative but not really useful here IMO.

 

[icetech]

This car was a victim of too much stiffening

 

[6PKRTSE]

I have home made torque boxes, frame connectors and a full 25.5 cage in one of my cars driven all over on the street. It is so rigid that I can jack up 3 corners of the car of the ground from one of the lower control arms. I have no body issues anywhere from being too stiff.

 

[torredcuda]

So would a heavy coat of paint I suspect. That was not really the question, unless what are you willing to settle for is any incremental improvement at all vs what the best or most efficient solution is to achieve the intended goal. Leaving anything on the table is not normally my style.

We can argue weld solutions all day long, spot welds can also be very close in effectiveness to proper plug welds. The test linked is using steel alloys not used in our era of cars and makes the test informative but not really useful here IMO.

Everyones goals are different, we don`t all need the same level of stiffness in the chassis.
I also stated " it will vary by material, application, production" in regards to spot weld strength. There are many variables but the premiss that some chassis stiffening will lead to spot weld failure is what I am arguing against as I have never seen that.

 

[j-c-c-62]

Fair enough for your life experiences, but the physics still hold true.

 

[j-c-c-62]

It is so rigid that I can jack up 3 corners of the car of the ground from one of the lower control arms.

I assume with a LCA that has been stiffened?
You really should be in the circus with that trick.

I have no body issues anywhere from being too stiff.

No comment on the personal stuff.

 

[6PKRTSE]

I assume with a LCA that has been stiffened?
You really should be in the circus with that trick.



No comment on the personal stuff.

Better. Tubular lower control arms.

 

[j-c-c-62]

I have yet to see any aftermarket tubular LCA replace a Mopar OEM LCA that is stronger/stiffer, period, and not sure how "better" is defined in this context.

 

[Dennis H]

This requires more discussion. Wait, never mind. Just took a ride down the Bascom Avenue destruction zone in San Jose. All questions answered.

 

[Kern Dog]

I did my frame connectors and torque boxes on the floor of my garage before I put in the car lift. I had 1.0 torsion bars and KYB shocks. Those in the know know how crappy the KYB shocks are compared to better brands but back then, I wasn't willing to spring $400 for better shocks. I measured, test fit, cut, shaped and welded in the frame connectors and torque boxes and then painted it all to look like it was what could have been done by the factory in December 1969.

I even included runs in the paint to make it more authentic!
(Accidental...try painting with a spray gun while laying on your side with limited movement!)

Afterwards, even with the crappy shocks, the car was quieter on rough roads. Rattles that I'd been used to hearing were gone. The car used to respond to road bumps with a reverberating thump-thump-thump that softened after the first thump. Afterwards, it would thump once. Why? I figured that the chassis wasn't flexing as much so the springs and shocks were more effective. About a year later I switched to huge 1.15" torsion bars and Bilstein shocks. One would think that going from 1.0 t-bars to 1.15s would result in a much firmer ride but in this case, the ride got better. I credit that to the shocks being a better match.
In short, I've read this and believe it: The chassis needs to be rigid so the suspension will have a stable platform to work with. If the chassis flexes too much then it is just another spring which means lost motion. A solid platform means that the springs and torsion bars could actually be softer yet more effective. You can look at this two ways: Install the connectors to then allow softer and lighter bars and leafs for improved ride coupled with better handling than stock OR install the connectors along with bigger bars and leafs to really step up your game!