Weld subframe connectors loaded or unloaded?

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HPP said:
For the driving ability of most of us on here, no, there is not going to be a discernable difference in unloading the t-bars and making things ideal. However, if you are a person who can feel the difference a half a tank of gas makes in the turn in characteristics of your car, then yes, you probably should make every effort to make things square, level, and blueprint ideal.
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I’m definitely not, I get caught up over details more than anything. It is more a case of ‘while I’m there’ as it wouldn’t be a chore to do so. I will be checking square and level as best as I can but I am confident it won’t be perfect.
 
J1MMY said:
Going to bookmark this thread as it’s a good point of reference.

This is what I’m opting for - nothing more than front and rear suspension, sat on its’ wheels. (Up on cribs)

Would completely unloading the torsion beams have any discernible impact…?
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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.
 
72bluNblu said:
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.
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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.

frame.jpg


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.
 
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.
 
Map63Vette said:
I'm planning to do mine with the frame on jackstands, but only because I found that the doors and windows worked better with it that way. I lifted it up on a set of QuickJack scissor jacks to do all 4 tires the other day and noted how much better everything worked. I also have cracks on my rockers at the back edge of the door, so pretty sure my car is sagging already and could use a boost before getting stiffened up again.
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This!!! ^^^^^^
Is what I have found on a few of my cars. 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.
 
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DionR said:
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.

View attachment 1716332321

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.
at 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 thoug
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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 was a fork in the road.. I welded them in where it stood. Done!
 
To me the best way to weld them in, is have the car on jack stands under the frame, we use eight jack stands. Shim as needed. Check to see if the car is level all the way around and your doors shut easy. If the car has any twist in it. Your car will always be that way if you weld them in without doing this. Unibody cars will always flex. That why frameties are used.
 
Just did mine over the weekend. I used 4 jackstands, one at each frame portion just in front of / behind where the connectors were being mounted. Checked my doors while it was sitting on the stands and the strikers were pretty much dead nuts in the center of the latches. Door hinges are in decent shape as well and don't appear to have much movement if you try to lift the rear of the doors with them open. I went the 1.5 x 3 x 0.120 wall homemade tube route with some angle iron on the front to sit against the bottom of the front rail for a little more weld area. No one will accuse me of being a welder in my free time by any means, but they seem to be in there solid enough. Only one test drive and commute so far, but car seems a lot flatter through turns and more settled over bumps. Haven't opened and closed the door enough to have a real good comparison, but when looking close after first setting the car back on the ground the strikers just skim the top of the latch now, so there is definitely still a little bit of sag in the car, even with connectors welded in. It does feel more solid even just sitting down in the car, like when you first "fall" into the seat. Car even seems quieter driving down the road, so kind of wishing I would have done this a long time ago.
 
I just did mine on a four post, an old alignment rack that I use. Everything seems fine and I’m happy with it, honestly I’m shocked how much less creaky the car is and how much better it feels in turns. The door is open in this photo for the record.

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I think y'all are over thinking it. Just put the car on 4 stands on the frame (suspension unloaded) and make sure it's level using the ticket as a guide. That's how I did mine on the 70. It worked great,.doors closed fine and you could tell an immediate difference afterwards when driving it.
 
Doesn't matter loaded or not, JMO.

I tack the connector to the torsion x-member, start jacking it up against the car, check door alignment, open/close door for best operation, find the sweet spot and finish weld them in.

As someone else mentioned the build tolerances on these cars are horrible. Wheel tubs with 1/2" more clearance on one side than the other and folks are concerned about likely less than 1/8" with connectors.

Got a car on a rotisserie, put a laser pointer on it near the rear spring mount on frame pointing level with rocker towards front. Piece of metal/cardboard up front and note pointer location. Flip the car over and see how much it changes. The one we did wasn't worth fretting about. Totally insignificant change.
 
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