Frame Flex Reduction

[BATurbo]

I've got my 70 C-10 frame on the rotiserre right now and when I go to rotate the frame upside down, I can see a fair bit of twisting flex going front to back. Does anyone have any past experiences with stiffening the frame so the flex goes away? I'm just starting to go back through this truck from the ground up and I'm leaning toward boxing the frame, but I don't know if I should add additional frame members before completing the frame boxing. Any info would be appreciated.

[LONGHAIR]

Boxing will do a lot for you as far as fixing flex. Extra crossmembers, unless well engineered and really required for mounting something , really just add weight w/o doing much else.

[BATurbo]

I appreciate the input. I've been doing a little research as to what direction I'm going to go with this. I'm flip-flopping between boxing the rails front to back or just in strategic areas. Do you have any thoughts as to what spots along a frame rail can I leave open and where I should box it in?

I'm planning on putting a torque on the frame along the long axis as it sits on the rotissere and then zero-in on where the flex is happening. Then mark the spot and box a 12" section and see if the flex goes away. This would minimize the weight addition, if it works. Let me know what your thoughts are on this idea.

[fine69]

Your frame is supposed to flex.

[4x4Poet]

It's a mandrel-bent, C-channel ladder frame with riveted and bolted in crosssmembers, so it will flex by inferior design (compared to superior cut & welded box-tube, for one). But the frame is meant to work together with the body mounts and body affixed. Meaning the frame flex is lessoned & tolerable with the body mounted. Poly body mounts further reduce frame flex over rubber. Energy Suspension makes a graphite-impregnated set with all hardware but bolts for less than just OEM rubber mounts cost.

That said, the front, riveted crossmember between the engine and the end of the front frame horns is notorious for have worn rivets and wallowed out rivet holes. Probably occurs because of engine weight and suspension flex stress.

Anyway, one can grind/chisel off the rivets, check the frame holes for roundness (weld & redrill as necessary), and bolt in that xmember for reduced flex and greater strength. Of course, use grade 5 or better bolts and nuts/washers. Be sure the bolt size fits the frame holes near perfectly. I've seen the bolted in xmember also welded in with just a few short beads on each side.

[kwplot34]

I would not worry to much about a bare frame flexing,and as sated above,the frame needs some flex in it.

[70cst]

I would think if the frame didn't flex at all it would not ride nor handle as well...but then again what do I know?

[BATurbo]

Thanks a bunch for the input. I don't want to make a bunch of work for myself if I don't need to, but, my long term plan for this truck is to eventually add a twin-turbocharged SBC that will have the capability of 1000+ hp, (Gale Banks - Bolt on kit). The frame stiffening is more for strengthening the frame to support the added power. I've seen the "Copperhead" truck that Stacy David built on the TV show "Trucks" a few years ago and I remember David saying that the 572 BBC he put in that truck was good for 600+ Hp and that the frame didn't need to be modified as it was strong enough to support that power level. I'm not sure of how much power the frame can handle without mods. Now that I have the bare frame to work on, I'd much rather add some strength now then wait till later and have to tear the truck apart to fix any problems.

[SCOTI]

Are all of the required crossmembers in & tight? If not, I would install them before measuring the frames flex. If they are installed & the flex you mentioned was still there, please do share your findings on the affects of adding the '12" sections'.

I've been curious about this as well. I modified part of the back of a frame so that area was boxed + reinforced. The frame was also cut from a lwb to swb & I was going to box + reinforce some more under the cab. Once I got to looking @ things, it's hard to determine when (where) to stop.

[Tx Firefighter]

I don't agree with boxing sections of frames. In my opinion, either box it front to rear or not at all.

Here is why...The unboxed areas will continue to flex while the boxed sections won't. This localizes a lot of stress on the frame at the ends of the boxed sections, leading to cracking.

In my opinion, a frame should flex. Think of skyscrapers and bridges, if they didn't flex, they would break. The engineers who design these things know a lot more than I do.

Besides, when has anyone heard of a sound frame under one of these trucks failing due to horsepower ? All you're going to do is break tire traction anyway. A 1000 horsepower burnout is the same as a 250 horsepower burnout. The tires are spinning all the same. If you intend to actually hook up 1000 horsepower, you've got significant frame and suspension mods in your future anyway.

[SCOTI]

I boxed the one section on my frame to offer additional support. My boxing plate was added under the lip of the frame rails to act like an I-beam would vs. a plate welded flush to the outside edge. It should offer more support then if not there @ all (frame splice). I also plated the inside & outside of the frame rail itself in the affected area. Overkill . . .....