ididieseler
Registered User
i'm looking to cut out about six inches a little ways behind the cab, how should I reinforce it when I splice the frame back together?
shortening a 1993 f350 frame to fit a '78 f250 body
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Oog
Full Access Member
If you need us to answer that question, then you shouldn't even be doing this job.
Welding a frame, especially on a pickup truck that may see loading and towing is important.
There is a major diffference between a strong welded section, and "Bubba, is dat there our pickem'up truck bed passin' us?"
Welding a frame, especially on a pickup truck that may see loading and towing is important.
There is a major diffference between a strong welded section, and "Bubba, is dat there our pickem'up truck bed passin' us?"
There's a thread similar to what you asking about on this forum and a couple where they just converted the older truck. I've read through 3 of them fairly recently, you just have to dig a little. And I don't remember the guy shortening his frame to do the swap.
antiqueford
Full Access Member
Z-Cut and Fish Plates. And a welder you'd trust your life to.
icanfixall
Official GMM hand model
Its my understanding that we don't weld on the frames. Now I was a welder for 30+ years in a major public utility power plant. So when I installed my 5th wheel and my goose neck hitches I welded to the frame. The goose neck was done with 1/2x6 inch plates from frame rail to frame rail. The 5th wheel mounts were welded directly to the frame rails. All 6 of them. I used 7018 stick rod on all of that work.I could have used 8018 too. 8018 is 1 1/4 chrome and 9018 is 2 1/4 chrome. 7018 is low hydrogen rod or commonly known as lo hi rod. I have not noticed any sag or cracks either. Now as posted.. Finding a welder you trust yours and others lives to is important. The idea of Z cutting and fishplateing the frame is a very good idea. Beveling the weld cuts in the frame is important to full penatration of the weld process. Look closely at the frame where you want to cut. Remember all the parts that are connected in that area and think about are they still going to connect there with more material welded to it.
HiHorse
Full Access Member
You can simply cut a straight line, weld it, then fish plate. The important part is to make sure every thing is clean and true before you put it back together. Stick, wire feed, flux core, tig, what ever you prefer to weld it with as long as you or the person welding is competent. The frame you are altering is not some special alloy that involves any particular process. It is only a higher tensile strength than mild steel (around 70,000psi). I do recomend the fish plate be cut as a diamond shape more than rectangular, or miter the corners generously on the rectangle. I have a vast amount of experience in modifying frames from 1/4 ton to class 8 trucks. Not all are going to require the same technic.
What he said.
Its easy to do but make damn sure whoever welds it knows what they are doing.
mudduck
Full Access Member
I took 8" out of the '90 frame to put my '79 stepside body on it. I did a straight cut and plated the frame. Im also boxing my entire frame though and have been a welder by profession all my life. I will have no issues with it. My build thread is on here if you want to check it out.
I have a welding tips book I bought long ago, and something that is preached in the book but has not been mentioned in this thread yet; They say if you are going to plate the frame, do not weld the plate all the way around and close it in with welds. Only weld parallel to the longer sides of the piece you are welding. In other words on a truck frame, if you are going to weld a plate on the side to help re-enforce your splice, only weld it on along the top and the bottom, do not make vertical welds and close it completely in.
They say as you weld the piece heats up and expands, and when it cools off, it shrinks back and creates stress. It's easier for the frame to expand and contract on along the top and bottom edges as you are welding, and then shrink back. If you close the sides in, it's very difficult for the frame to swell up and then contract when it cools, and it's also almost impossible for the plate to swell up and then contract back when it's already welded on the top and bottom. All looks good when you are done, but you don't realize all the stress the area is in just sitting there, and then when it's put in service it usually eventually cracks somewhere along one of the welds.
They say as you weld the piece heats up and expands, and when it cools off, it shrinks back and creates stress. It's easier for the frame to expand and contract on along the top and bottom edges as you are welding, and then shrink back. If you close the sides in, it's very difficult for the frame to swell up and then contract when it cools, and it's also almost impossible for the plate to swell up and then contract back when it's already welded on the top and bottom. All looks good when you are done, but you don't realize all the stress the area is in just sitting there, and then when it's put in service it usually eventually cracks somewhere along one of the welds.
HiHorse
Full Access Member
That's a neat book you have there, franklin2. That is a good technic for a "truck" frame, but does not equate to a "pickup" frame. If anyone is concerned with residual stress, simply post heat the area and allow it to cool. Even more importantly, do not weld on the radius of the "truck" frame, as this is were cracks generally develop.
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