Weld subframe connectors loaded or unloaded?
- Thread starter Dantra
- Start date
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I really do not understand the obsession with welding the subframe connectors in while the car is on its suspension.
The chassis wasn't loaded at all when all the suspension points were welded on at the factory. The factory frame dimensions listed in the FSM were almost certainly taken from a bare chassis if not the jig itself, not an assembled chassis sitting on its suspension. If anything, the chassis is likely to be closest to its factory configuration when it is fully unloaded.
The only reason to have the car loaded on its suspension is if you're trying to avoid having to reset your door gaps, so if your car is fully or nearly fully assembled and you don't want to change anything then welding the subframe connectors in while the car is sitting on its suspension is the best chance of keeping stuff like that exactly the same as it is. But quite frankly, I think there's a better argument to be made for leveling the chassis without any of the suspension installed and welding in the connectors then. Yes, you might have to make a door adjustment because afterward the car might not sag as much as it did before when it was sitting on its wheels, but that's a GOOD thing overall. Even if it meant needing to make a small door gap adjustment.
A fully assembled car sitting on its wheels is more likely to have some kind of twist. If you've ever checked the corner weights on a car you know they're almost never equal unless you've gone to great lengths to make them that way. And if the corner weights aren't balanced, well, the chassis isn't neutrally loaded. Now, if the goal is not making any body adjustments on a fully assembled car, then yes, car on its wheels and everything loaded will accomplish that. But if neutrally loaded and square is the goal then a bare chassis that's been leveled is a better bet.
And realistically, as I said earlier, unless you go out of your way to put a twist in the darn thing there's still going to be plenty of flex in the chassis when you're done, so it's pretty unlikely you're gonna weld a permanent twist into the chassis unless you're really trying to or really bad at this. Subframe connectors overall make the chassis stiffer but they sure as heck don't eliminate all the flex, not even close.
DionR
Well-Known Member
Yeah, you are probably right. I think my fixation was due to knowing someone that did it on a 2 post lift and the car was either really hard to get good door gaps or impossible to do (can't remember which). I know they welded a bow into the car, that I am certain of.
I think the difference is that the factory didn't weld it all together with a drivetrain in the car. Hanging a motor and rear axle past the points of support on the chassis will put the car into a state different than the factory had it when they welded it all together.
But in retrospect, jack stands will give a better datum for the chassis than supporting it on the suspension.
At the very least, if someone was looking for perfection and didn't have the drivetrain out of the car, I think they need to support the car at 4 points. One set just in front of the trans crossmember, one set at the front of the rear frame horns and one set at both the front and rear bumper mounts. And those points need to be measured to match the below image.
In theory, that would put the chassis in an "as factory" condition.
What if they design things so that whatever flex the chassis had when it was complete and sitting on the suspension would set the gaps to where they wanted them? If so, that would be the state I would want to fix the chassis at. Kind of a long shot that they would be able to plan ahead for that though.
mopowers
Well-Known Member
I've done it both ways and the result was the same - a stiffer chassis. Don't overthink it. If the doors open and shut well, burn them in.
This!!! ^^^^^^
Is what I have found on a few of my cats. Doors hood and trunk open better when it’s up on jack stands.
IMO, if this is the case, then do the welding like this.
Map63Vette
Well-Known Member
Figure too that at the factory they would have been working with brand new sheet metal, not stuff that's 50+ years old with rust, corrosion, potentially broken welds, fatigue from loading, etc. At the same time remember it was an assembly line and they were cranking these things out by the thousands, so I'm guessing things weren't fixtured super tight and accurate for each and every car. I'm sure there was some amount of tooling (whether via fixture or "self tooled" parts that naturally align themselves), but after a few years and thousands of cars I'm sure the odd car made it through with less than ideal specs when someone wasn't paying attention.
IIRC, factory tolerance was +/- .125", so yes, pretty sloppy.
I think all of us would agree that flat and square clamped on a jig would be best. Flat to blueprint spec on multiple jackstands is a reasonable compromise. Putting them in on a car that's built, painted, and complete while sitting on the tires is probably going to work for most of us as well. Thats because most of us will notice the increase in rigidity more than we will notice if something is off by .125 of an inch.
I think all of us would agree that flat and square clamped on a jig would be best. Flat to blueprint spec on multiple jackstands is a reasonable compromise. Putting them in on a car that's built, painted, and complete while sitting on the tires is probably going to work for most of us as well. Thats because most of us will notice the increase in rigidity more than we will notice if something is off by .125 of an inch.
DionR
Well-Known Member
I always do mine with the seats and carpet out.
I think you miss out on all the real excitement of welding them in if you do that.
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