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Sub-Frame Connectors - When to install

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Well, just as usual, waiting on parts.... So looking for ways to advance the build.

Can Sub-frame connectors be installed (welded in) if:
  1. There is NO SUSPENSION installed(waiting on parts)
  2. The car is resting at 4 corners but ON THE Sub-Frame - 4 furthest points, 2 in the front, on the rail, just behind the front wheel and 2 in rear before the axle
  3. The car is level in both directions
Theoretically, the fame should be flexed as if it were on wheels.

What do you think? Can they be fully welded in place?

Thanks in advance.
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I installed mine with the car fully loaded with engine, trans, etc. I used a forklift to lift it 2 feet in the air and set the wheels on blocks...did some initial welds...then finished up the welds once the car was on the rotisserie. Others have installed them while the car is on the rotisserie...I am not sure you are going to find any type of definitive answer.
 

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Discussion Starter · #3 ·
I installed mine with the car fully loaded with engine, trans, etc. I used a forklift to lift it 2 feet in the air and set the wheels on blocks...did some initial welds...then finished up the welds once the car was on the rotisserie. Others have installed them while the car is on the rotisserie...I am not sure you are going to find any type of definitive answer.
I am not sure either.... but, thanks for your input. I did not have the opportunity to do anything while the car was rolling..... let's see!
 

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Started with my coupe body on a rotisserie with no drive train.
All new metal.
Door gap changes as I transfered it to jack stands. Wiill change again Im sure after I load up the drive train. So back on the rotisserie to install sub frame connectors. Then load up with drive train. Then I will finish setting up my door gaps (much cutting / welding the door edge to get my dynacorn doors to match original quarters).
I suggest you install the same way wicked93gs recommends.
Good luck!
 

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FWIW…convertible inner rockers, torque boxes, and torque box gussets are a much better solution. If you want to go farther, the convertible one piece seat riser is a nice addition.
Everyone says this....but I am not sure I agree 100% about the convertible rockers. Would I have installed them if I knew about them when I was at that point? Probably, yes....but in effect all convertible inner rockers do is make the rocker panel bigger and tie the frame rail and the rocker panel together better with the aid of the torque boxes. The same thing can be accomplished with what I did...using "jacking rails" to tie the rockers to the frame rails and SFCs. What people don't mention is that using convertible inner rockers loses you foot room...not a big deal to most people, but I have big feet. So if it were today and I had to make the choice on a new car of installing convertible inner rockers...I would pass and do what I did the first time.

Th convertible one piece seat pan undoubtedly adds a lot of strength....but the downside from a modification point of view is that if you want to do something like cutting down your seat pan height for more headroom, it becomes problematic to the point you would lose most of the strength from installing the convertible pan to begin with. That being said...convertible lower seat pans and that bolt-on brace they use seem to come with no interior fitment downsides. I would have installed those myself if I didn't have SFCs and jacking rails I would have had to cut them up and install them piecemeal around(if the car were on the rotisserie in front of me today I wouldn't care and I would do it anyway)

Its one of those things that would heavily depend on the build in my eyes. To be clear....I also don't believe just adding SFCs is going to do much for a car aside from helping prevent A-pillar paint cracking on its own...but I think they can be useful if used a based for more extensive modifications.
 

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Input the values of the cross sections for convertible rockers and then compare that to any subframe connector on the market. Don’t forget the orientation of subframe connectors to convertible inner rockers. All the ones I remember are wider than they are tall…not that it will make a difference in this case, but just for a direct comparison…and consider the orientation in which they are installed in a car.

After that double the value for the convertible inner rocker and although not exact you will be close to the strength of the two rockers halves welded together. Then compare that to the messily number you calculated for the largest subframe connector you can find.
 

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Input the values of the cross sections for convertible rockers and then compare that to any subframe connector on the market. Don’t forget the orientation of subframe connectors to convertible inner rockers. All the ones I remember are wider than they are tall…not that it will make a difference in this case, but just for a direct comparison…and consider the orientation in which they are installed in a car.

After that double the value for the convertible inner rocker and although not exact you will be close to the strength of the two rockers halves welded together. Then compare that to the messily number you calculated for the largest subframe connector you can find.
I don't doubt the math...but I never suggested installing the SFCs by themselves(I don't see much point in that). I never even suggested SFCs were better than convertible inner rockers. What I said is that convertible inner rockers come with downsides that may not be suitable for every build. The exact same thing applies to SFCs to be honest....but SFCs do not intrude into the interior and cause issues for me there. For references...this is what my undercarriage looks like:






The DOM SFCs are tied to the floor with contoured "sidewalls" made from a 2nd set of SFCs, the SFCs are then tied to the "jacking rails"(again, DOM tubing) which are then tied to the rockers. rectangular tubing runs under the lip of the cowl and ties down to the rocker...from the rocker and that under-cowl lip tubing more bracing ties it to my "outer shock towers"...and finally I have a "trunk brace" like just about every coupe on the road made after 1975. Is it rigid? You bet it is. I can jack the car up under the front torque box and by the time I can get a jack stand on its lowest setting under the SFCs the rear wheel has come off the ground. If I don't have the engine in the car jacking the car up and the rear torque box will cause the front wheel to lift off the ground before the rear wheel(well, when it had leaf springs anyway, haven't tried that with the 3 link).

Would this be better with convertible inner rockers? Possibly...but at this point its rigid enough to meet the requirements of my build and I doubt I would be able to tell the difference if I added more rigidity...and I still have my foot room. To be fair though...that is a lot more extensive than just some SFCs. If the choice was between just SFCs an convertible inner rockers...yeah, I would likely opt for the rockers.
 

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This would help you know if your body is straight. I would add SFC if these measurements were very close, if not spot on.
Font Rectangle Parallel Engineering Schematic
 

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Well, just as usual, waiting on parts.... So looking for ways to advance the build.

Can Sub-frame connectors be installed (welded in) if:
  1. There is NO SUSPENSION installed(waiting on parts)
  2. The car is resting at 4 corners but ON THE Sub-Frame - 4 furthest points, 2 in the front, on the rail, just behind the front wheel and 2 in rear before the axle
  3. The car is level in both directions
Theoretically, the fame should be flexed as if it were on wheels.

What do you think? Can they be fully welded in place?

Thanks in advance.
Those are the $64,000.00 questions I have been asking myself for the past year. I have decided to wait until all of the drivetrain is in and wheels on. I know it would have been easier doing it while on the rotisserie. I have a convertible so there will be a bit of flex. I'm also doing the body panel alignment after the driveline is in then I'll do the SFC last.
I did do a test fit on the SFC to make sure it will fit. I know I'll make a mess of the paint I've done on the underbody when I weld them but I can repaint as required. I may be over thinking everything but in the long run I may be glad I did.
 

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"Sub-Frame Connectors - When to install"

a. When you have "extra money" to spend and nothing better to spend it on.
b. When you want to add extra weight to your car with no added benefit.
c. When you feel like adding impediments to future work like running fuel/brake lines or side exhaust.
d. When you listen to people's stories about how much more rigid the car "feels" after effectively reinforcing the floor under your seat.... and remembering that nobody wants to claim they spend hundreds of dollars on something that really didn't do squat.

Oops, did I really say that?
 

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@Woodchuck :LOL: Tell use how you really feel(thems some big words...literally). I wouldn't say they do nothing though. I use mine all the time to jack up the car from less-than-ideal angle! :p However...I have been known to waste money on this car...repeatedly and will likely continue to do so.
 

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In a contest between Woodchucks car with convertable rockers vs Wicked93gs car for torsional rigidity...........my money is on Wicked93gs..........!!!!!!!!!!!!!
I have to say @Woodchuck and @patrickstapler are 100% correct when they say convertible rockers are more effective than SFCs in a direct comparison. Obviously Ford also thought so when they built the convertible...they made no effort to tie the frame rails together in any way. Its pretty hard to out-engineer Ford after all...they do a lot more testing than any individual ever could.
 

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I have to say @Woodchuck and @patrickstapler are 100% correct when they say convertible rockers are more effective than SFCs in a direct comparison.
I meant to compare your car to his in your cars' current configuration with the modifications you have made to the SFCs. I agree that in a direct comparison the SFcs connectors are less effective. I believe that with the modifications you have made that the reverse is also true.

@Woodchuck opinion of SFC is well known to anyone who has posted in any way about SFCs on the VMF. I somewhat agree he has a point but he takes it too far in saying that they do absolutely nothing.
The floor supports are a torsion box in all their light gauge glory and the SFC does slide inside them and shortens them which does stiffen the torque box somewhat. I do believe that it doesn't take much modification to improve them by adding additional outriggers to connect them to the rockers or the torque boxes or both. I think this is what you were saying about them?
 

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I have no numbers to back it up concerning adding subframe connectors but I can tell you what happens on off-track excursions without any subframes.
That equals a unibody that's a mess to fix afterward. (I have seen that one firsthand)
I was told when I worked at Global that the only support better than the subrames WITH the supplement kit was what you'd experience with a cage.

I like that photo..... very difficult to find photos with that kit installed. Probably because not too many builds start from the rotisserie.

For the original poster, I've never installed structural stuff that wasn't on an assembled car that rolled into the shop. It for sure can be done though.

ex-Global West GM
1991-1995


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Here are my limited experience thoughts on the subject.
If Ford had installed them at the factory, they most certainly have done it during body assembly just like the installation of any full frame vehicle, not wait until the suspension and engine installed. Not everyone has the luxury of installing in that manner and weighted body may be the only way.
I installed mine on the rotisserie, bare body and subframe. I took extensive measurements with it sitting level, raised in the air and tilted on side for access. There was zero changes as I tilted it. Mine is a fastback though and I sure that a convertible would require some welded in support to minimize flexing that I didn't have to deal with. After installing them, it really looked complete and MUCH stronger. Just really looked complete.
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As far as convertible rockers, I totally agree that they would have been the stronger solution and I might have considered it if I was aware of the option. I would have weighed out the downside of their taking up space in the passenger compartment. I did however go with the convertible one piece seat pan for their lower seating position and additional rigidity.
 

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I wouldn't do this without subframe connectors.
View attachment 866420
Now that's something you don't see everyday lol.
Long time ago I was at a car meet with my 65 convert. Just wrapped up a resto which included new inner rockers, floors etc. Camaro guy comes up and asks if the car has plastic wedges between door and quarters to maintain door gap, like his car does. I say no. He implies that is BS. I say no. He walked away not believing me. My story has minimal relevance to your post, I just like sharing what little I know with others lol
 
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