Frame torsional stiffness

[dunce79]

Trying to decide how far I need to go with the frame for my 59 Fleetside shortbox frame. It'll be a daily driver that I want to handle well but I don't forsee doing any autocross type stuff with it. It will be dropped with a 73 firebird front sub frame and a fatbar 4 link - may do a c-notch but not looking to lay frame or be that low. Performance stance you could say...

Anyway, I planned on possibly boxing the frame from the front sub on back but after that I'm not sure. Can the frame be stiffened up enough with a couple cross members or would it be better to go with an x-member? Maybe thats overkill for basic street use? Kind of complicates things with the drive shaft, exhaust, battery mounting ect too.

Thoughts?

Thx.

[Ziegelsteinfaust]

X member would be the best rather bolted in or preferably welded, but if mild fun you would likely not notice the difference.

On my C20 project I was contemplating I was just going to add 3 cross members from a truck I could of gotten for $500 with a service bed I wanted. Then I was going to make the transmission cross member more structural then it is from the factory.

Either way you should be happy with the results.

[andrewmp6]

Have you looked in to a frame swap ? http://www.e-zchassisswaps.com/kit.php?category=5 as a kit to use the 73-87 gm truck frame.

[theastronaut]

I started this topic about stiffening up the frame for my '66, has some ideas thrown out. I haven't finished the bracing for mine yet due to changing engine/transmissions and reworking the front crossmember. The idea is there though.

http://67-72chevytrucks.com/vboard/s...d.php?t=495785

[scottybaccus]

I build custom chassis for '47-'53 GM trucks. One of the things to keep in mind is that the frame is fairly light weight, really up into the 1960 and later models. All of the cross-members are riveted, and this frame flex was intentional. It is the reason so many of these chassis survived for 65 years, crack free.
If you plan to stiffen one, it is an all or nothing scenario. Welding in the cross-members, without boxing the rails, will only lead to cracks at every joint. You can get a very rigid frame if you start by boxing the rails, then enclose the intersecting cross-members that were riveted in, to arrive at a tube frame that looks stock. Adding additional structure, like a K or X in the middle will finish the job. Porterbuilt has one they use for a trailing arm suspension base, with the transmission mount built in. This design has been in old school hotrods for decades. It works well, but take note that it isn't flat. It is three dimensional. That is key.

For my chassis, I opted to leave the rails unboxed, and let the rivets do what they do, but I have designed a bolt in IFS cradle and a bolt in trailing arm cross-member and rear suspension cradle. These stiffen things somewhat, but still allow flex at all the original points that would crack out if they were welded up.

[lower50's]

Just box in the frame and add some cross members. I'm using an s-10 front half boxed and will have a K under the cab. Should take my 500 lb-ft

[dunce79]

Yeah, kinda thinking putting a K in just a bit behind the camaro subframe and box it.