A buddy is going to weld in the full US Cartool stiffening kit into a 71 Demon. He wants to put it on a rotisserie to do it so the the welds will go in better. Plus it's easier than laying on your back.

I thought that I had read the it's best to have the car on all fours to weld in the frame connectors.

Any opinions?

If the car has no engine, trans , rear axle or suspension, you should be fine. It is the weight of all those things that induce flex, requiring the weight to be on the suspension to keep everything in line.

He could tack it in place with the car on jack stands and then seam weld it when it is in the air.

decades ago a local guy had em done & he said the guy jacked the car up in the middle of the stiffeners then finished welding em in (that is all I remember (fwiw). Not my area at all but off the top of my head I would want it completely loaded & up on all fours then weld em. EDIT he said he "slightly" jacked em up in the middle of their length then finish welded.

The guys at US Car Tool suggest pushing the floor down in places to contact the connectors. Those connectors are not all that great of a fit to begin with. In hindsight I would have used square tubing. But you don't need to weld the full length, a few 1" beads along the length is sufficient. Seam seal the whole length when you're done.

A friend installed frame connectors (not sure of brand) on his Duster using a rotisserie, then when it came time to align fenders and doors, the body was twisted. He may have attacked project wrong, which caused issue, but with the body inverted it might cause some issues (weight and not all sheet metal present). There are many cars out there with connectors, so there has be a good technique.

I X braced my door jams & X braced the inside of the car from side to side also before I put it up on my rotisserie. I was going for the sleeper look so I hid my frame connectors inside the rocker panels.

We installed the ones on Dads 72 Duster using the stock suspension and the car setting up in the air with all of the weight on the suspension. I left the wheels and tires on the car and used eight wheels 4 14" and 4 15"...It might look like he!! but it was very stable and worked out well...
If you get it up high enough it isn't a bad job at all...The doors on his car close just like they did in 72 and never needed adjusted. I'd install them again this way if I have to...
As mentioned above it does help to have something a little heavy to set in on the floor pan and help close the gap to the frame connectors when welding to the floor pan...Mine fit very well once mocked up...
Maybe next time I can use the 4 post lift...

I used 2x3 tubing for frame connectors on my '64 "B" body. Very easy to do and VERY strong. Had the car up on jack stands with all the running gear removed including fenders and doors. Doors are back on and close perfectly and the fenders aligned with no problems. The car was put on a rotisserie after the frame connectors and floor patches were welded in but that was for removal of the 60 year old undercoating and ease of assembly of the fuel system and brake lines.

I have welded them in both ways, as a couple said if the drivetrain is stripped out a rotisserie is the way to go, much better welds and just easier all the way around. If the drive train is in it, then I do it on a lift, I weld the connectors in the back on the spring perches and use a floor jack to push the connectors against the floor, and then check the fit of the door gaps before I weld them to the torque boxes. Then I lift it up and finish welding on a rack. I like to put them in under tension with a jack loading them, it just seems to make the car stiffer.

I did the ones on my 64 while up and supported by the bumper bracket holes only. It was also tubbed and the 1/4 panels stretched at the same time. Body fit is perfect. However I wouldn't cut the frames rails (inboard springs) or do full 1/4's without additional support.
Doug

I did mine the same was as centerline said he did his. Turned out great. Perfect fit everywhere.

I've done it both ways and each came out fine. If the car is on a rotisserie already then do it. If not then do it with weight on wheeles

If a car ended up twisted from the installation of frame connectors while on rotisserie, it was twisted before it got there.

Ok, good stuff.

Thanks