My question is, where do you cut. Coming from the back, the frame gets narrower and angles inward on both sides, between the rear tire and the cab (where it makes since to cut). Under the cab, the frame goes down. Cutting under the cab would mean relocating the rear cab mount x-member too, right. Pictures, anyone?

 

A bumpside I came across that has good pics of the "Z" section







Josh

 

I don't like the diamond welded in the back.
The point of stress is on the bottom flange. It would be in tension and would tear first when loaded.
I think the bottom flange and inside vertical should be doubled, fish plated on the inside of each frame rail, welded and then drilled and bolted just for insurance if a weld ever let go.

 

That looks like a bump body on a dent side frame. So that angled section really will meet up at the front when you cut and fit it? I didn't think it would. Anyone else with pics, please toss 'em in.

I'm trying to decide if I want to cut one of my lwb dent side frames, or do a massive amount of work and use a swb bump frame I got (it's still gonna be a '74 dent side body either way). I'm really at a fork in the road for this project. I have nearly every part I need in triplicate, Just missing a few odds and ends, then the assembly begins.

 

Most definately a 2WD bump frame. I have followed that dude's build-up since day one. His write-up is on a competing Ford Truck website.

I guess the clue is, you are using a Highboy 4X4 frame?

Josh

 

Trucks! on Spike TV shortened a 66 C-10 from a long bed to a short bed in early 2009. I understand from this show and numerous other articles I have read that it is the proper way to "Z' a frame:

They took out about 16 inches from the area behind the cab so they didn't have to reinstall the cab mounts. First some scrap stock was welded between the frame rails to keep everything square. Basically then took out two sections 16 inches long from the top half of the frame and then 16 inches from the bottom and then overlapped the sections. The advantage of this method is the amount/length of surface area to weld. After dressing the welds, a "fish plate" (similar to above) was welded on the insides where they couldn't be seen.

If the above doesn't make sense, visualize "L-7". You can do it with your hands... Make an L with your left hand and a 7 (pointing finger down and thumb pointing left) and put them together.

I believe the important things to keep in mind is to keep the halves square, level, and have really good weld penetration. Our frames are 3/16 thick so even a 110v welder can do the job - again, only if proper weld penetration can be achieved. I suppose it wouldn't hurt to also bolt the fish plate with Grade 8 hardware just in case.

On another project ("Das Bronco"), the guys added 1-inch welds to the cross members that were only riveted in place to improve torsional (twisting) stiffness.

HIO Silver
73 F100 4x4, 390FE, NP435, NP203, +4 on 35s

 

Nope, I have the choice between a 2wd '67 swb F100 or a 2wd '74 lwb F100 or a 2wd '78 lwb F100 frame.

I know the highboy and '67-72 frames are alike in that they don't widen in the rear. My '74 frame does. That's the one I'm considering for the cut, and that's what makes it more difficult for me to figure out. The rear frame spreads out about two inches on each side.

Cutting the bump side frames is easy to figure out.

My swb frame needs a few rust repairs and I need swap on the 2nd cross member, torsion mounts, front cab mounts, shock towers, and axle mounts from another frame I have. It also needs new springs (I'm considering mounting a set of '90 F150 springs w/ a hanger flip), and the narrow rear frame makes finding an in-frame rear tank more expensive. The narrow rear also means that I'll have the re-weld the spring perches and shock mounts when I switch the springs and rear axle, it even messes with my sway bar choices.

I assumed the guy was using a dent frame because of the top rear shock mounts. Those look like dent side shock mounts. The ones on my bump frame are different. They have a horizontal stud that the top of the shock slides onto, as opposed to the pedestals on the dent mounts, with a hole for the post on the top of the shock.

 

My f100 2wd frames are only 1/8 in thick. I saw the Trucks! episode. I understand the different fitting methods too.

The issue I have is with the dent frame being 4 inches wider in the rear than in the front. The width is all gained right where the frame needs to be cut.

Thanks for all the info so far everyone.

 

Wanted to share this write-up on frame shortening (if the censors allow it)

How to shorten a LWB frame - The 1947 - Present Chevrolet & GMC Truck Message Board Network

What I like is that he didn't make 90 degree corners, but instead rounded the turns to avoid stress cracks.

However, a couple of the heavy duty truck shops that both shorten and lengthen frames use a technique similar to the bumpside I posted.

I am finding those rear shocks on the bumpside intriguing now. Were the mounts changed during the bumpside era? Say 67-69 had dual eyelets and then 70-72 had what the dentsides had?

Josh

 

Ah I get it now... Then I'd locate the straightest frame section and do the Z cut there even if it is under the cab. Relocating the cab mounts is less hassle than cobbling the tapering frame widths.

Btw, I think you're right about the shock mounts. Mine has the through-holes an my brother's Bump has the studs.

HIO Silver

 

Hello, I worked in a truck shop in Oklahoma city for a couple of years and we shortened and lengthened many a big truck frame. All we ever did was square cut them. It is so much easier to get your measurements correct and square and all of that when you square cut it. We did glove the frame atleast 12" each way from the weld and then weld and bolt all of it togeather. Never had a issue with any of them. Heck on some of the Macks they were already gloved so we would put a triple glove in them.

The diamond fishplate is kinda the standard except we would usually not have the diamond come togeather on the horizontal end if you can understand that. I have been welding for a living since around 88

 

The problem with "under the cab " is that the frame goes down, wouldn't that create a hump in the middle of the frame when I welded it back?

 

Could you PM me a link to the write-up you are speaking of?