So, apparently I own a 76 K25. I buy things on impulse.

After having looked around at plenty of pictures of similar trucks flexing their frame more than the suspension, I've figured I might want to consider addressing this before I do much else.

To me, the ideal way to do this would be to make a template of the side of the frame (say cardboard), and transfer that template to a single peice large peice of steel. Then burn 'em out with the plasma or torch. My reasoning being to avoid the evil of a vertical weld if you make the 4th side out of more than one peice of steel. Practically, I can't do this. It would be too large of a peice for me to easily handle, and would present a lot of waste (equalling wasted money)

Which leads me to thinking that making the 4th side out of segments of appropriatly sized flat bar would be an aweful lot easier. Which means you need to either have vertical welds, or fishplate every added section, or to put fishplated doublers over each vertical weld (I've heard them referred to as 'scabs' but don't know if that is entirely correct).

So, my question is... If I box it by throwing a bunch of segments of flat bar on there with vertical welds connecting them, will I run into trouble? Everything I've ever read about chasis design says I should. But, the textbook and the real world are often a different place.

im runnin different sections not even vertically welded together because of the factory crossmembers but i havent wheeled it yet and it will be getting a cage before it gets wheeled too

I'm really happy with how I did mine. Not a Cheby, but...

Frame work starts in Post #4 & continues thru the first page or so.

http://www.pirate4x4.com/forum/showthread.php?t=564005

Good luck. :smokin:

I don't see the problem with vertical welds. I wouldn't even think that you would need to fish plate each joint either, as long as you had good penetration on the welds. I'm sure many people will have different opinions on this but, either way you do it, it will be stronger than before.

If you are going to wind up using a few different plates for each side, say 4 pieces per frame rail, I do not see where fish plating it will really help to make a difference other than maybe adding more weight, with a boxed frame which it will be when you get finished, it should be plenty strong.

Just get some 1/8th inch plate, cut it out to fit the frame, weld it in.

Fab up some new crossmembers.

Good to go.

My problem is that strength and fatique life, while related to each other to an extent, are two different things.

But I guess I shouldn't worry about it.

For crossmembers, how involved do people get? I've seen guys buck the front one out, and put a bent peice of tubing in instead... What about the rest of them?

each crossmember is designed for its placement. the front crossmember has a bend (keeps it stable laterally, then the engine crossmember has a bend and offset mounting, which tends to crack.

the next crossmember is the transmission crossmember, which people will usually leave most of it in the trash when reinstalling it...

Behind and above that crossmember is the main cab support/ load carrying crossmember, at the back of the cab, above the spring mounts. its designed to keep the frames upper and lower edges from twisting out sideways, and keeping the C shape upright.

on a blazer, the next crossmember behind that is one above the rear axle, in front of the fuel tank, supports the fuel tank, keeps the frame stable.

then theres the rear crossmember, tying the rear frame rails and spring mounts together.

If you take each crossmember out, and design a replacement for it that somewhat duplicates the manufacturers thought in stress and weight bearing, you should be ok. You could use round tube, and go through both sides of the frame *(inner and outer) like a newer frame and that will give you structural integrity.

You can keep it light, design it to hold up to serious abuse, and have a frame that will NOT flex. just takes some work.

You could use round tube, and go through both sides of the frame *(inner and outer) like a newer frame and that will give you structural integrity.

You can keep it light, design it to hold up to serious abuse, and have a frame that will NOT flex. just takes some work.

This is something I want to do with my 98 GM. I was thinking that adding a few and replacing whats there with tubular crossmembers would give the frame more torsional stiffness.
I want to remove the factory front crossmember where the old IFS stuff bolted to and add one through the boxed factory sections above where the old one was but I wasn't sure if cutting the holes through it would weaken it.
As far as boxing it goes can only sections of it be boxed? I think a weak area is behind the cab where the curve in the rails are and wanted to plate the inside of it to the center of the rear axle and maybe 1ft into the strait section under the cab. This and add a tubular through it after. Is this a waste or worth it?

Well, I know you can box only part of a frame, if you wish... My 94 dodge 2500 CTD has a boxed frame from the front till about the transmission crossmember. Then it's just a regular ol' C channel all the way to the rear bumper.

Personally, I figure 'since I'm under there' I might as well do the whole thing, or not at all.

I was thinking I wanted to replace the trans crossmember anyways, I want to tuck the belly up on it till it's all flat. The truck has a body lift, I'm not crazy on that, so I think I'll move the driveline (and unfortunatly the saddle tanks, which will stay) to about where I'd like them, then hack the body lift down as much as I can.


Loveshackle's method seems to make sense... Anybody else got pics of how they did it?

Fuck the saddle tanks. Get a Blazer gas tank or get a bed mounted fuel cell.

I got the cell, I fucking hated those damn saddle tanks.:mad3:

Check out 72Blazer's boxed frame:

http://www.pirate4x4.com/forum/showthread.php?t=518926&highlight=boxing+frame
http://www.pirate4x4.com/forum/showthread.php?t=604784