Long bed to short bed conversion

[MarshMobbin907]

I'm in the process of doing a short-bed conversion and it's a lot of work, but to me it's worth it. This is not a daily driver so I've been able to take my time. (Although at this point the project is occupying all three garage spaces at the house and winter is coming...) I used four jack stands with 4x6x48 wooden beams across each pair to support the frame. One support under the rear of the cab, one behind the front rear spring hangers. I used a 3 inch "Z-cut" with an cut off wheel in an angle grinder. I also paid a mobile welder ($60.00/hour @ 3 hours). It lined up very nicely. Frankly, that was the most nerve-racking but actually the easiest part of the project.

I watched a YouTube video of a guy doing his frame and he said that a pro from his home town said he like the horizontal cut more so I think I might go that direction. How many inches did you take out of the center? I think I remember him saying 12 and an additional 4 at the rear

 

[Jrgunn5150]

Your logic in the initial post is sound, on level ground, measure measure, cut and weld... But shortbed frames and trucks are pretty common still.

 

[Jrgunn5150]

I watched a YouTube video of a guy doing his frame and he said that a pro from his home town said he like the horizontal cut more so I think I might go that direction. How many inches did you take out of the center? I think I remember him saying 12 and an additional 4 at the rear

If you do a horizontal, or "S" cut, you get more weld area. However big trucks are straight cut, like dump trucks and whatnot, so whatever you like.

 

[MarshMobbin907]

Think I'm going to give horizontal shot, does anyone happen to know the exact measurements that I'll need and in what areas?

 

[smoothandlow84]

I shortened my longbed frame to a shortbed. Not difficult at all. Just paln ahead and I HIGHLY recommended a vertical to horizontal then back to vertical cut when notching the frame. Dont just cut vertically...it wont be strong enough no matter how its reinforced. Definately do it correctly so everything lines up equally and you get more weld contact. Working on a level surface is key, support the frame with jack stands equally (double check the measurements. I made my frame cuts just behind the front section of the saddle tanks. From memory...I believe that I removed about 12 inches from the original longbed up front and cut a small section off of the back of the frame. I just took measurements from the front of the shortbed to the center of the wheel tubs. I then transfered those measurements to the longbed frame. Why most people are intimidated by doing this....I dont know. Shortbeds, at least here out West are harder to source for a decent price. My main reason for the conversion was that longbeds at least here are abundant and on average go for 1/3 the asking price of shorties. My longbed truck was $2350 running and driving. The shortbox was $135. I sold the longbed which was damaged on the drivers side for $100.......

Shortbed trucks running and driving.....average over $4000.


So I am still ahead of the game and made my truck what I wanted it to be.......at least for now.


And for what its worth...I used a Lincoln 110 volt wire feed that has the capacity to weld a single pass weld for up to 1/4" thick steel. The steel on these squares isnt as thick and robust as most people think. Using a 110v wire feed with gas is fine. Anything else is just plain overkill. If you arent a competent/experienced welder or you would feel better hiring a welder, then go for it. I have been welding tig, stick, mig and acy/oxygen for over a decade. I am confident in my welds and my abilities. I also used a sawzall to make my cuts, using a 1/2" drill bit to drill out the intersecting cuts first. I also welded 3/16" thick steel backing plates on the inside sections of the frame where the "z" cuts had been welded. Some others who have shortened frame like using plasma cutters, but they tend in my opinion to make messier cuts. The smaller the gap to weld, the better and stronger it will be. Accuracy is key...measure three time, cut once.


You will need

shortbed saddle tanks (if you want dual tanks)
Shortbed driveline
cut and shorten the parking brake cable
shorten the rear tail light wiring harness
And.....often overlooked...a shortbed from a donor truck that also has dual saddle tanks (I could not source a shortbed with dual tank doors, so I removed the door from my longbed and grafted it onto the shortbed.)

 

[1987 GMC Jimmy]

So I'm sure this is a repetitive topic, but I just like some baseline tips for a first-timer. I've watched quite a few videos and read even more Forums on this subject and a lot of people have different ways of doing it. I think I have the gist of it, new brake lines, fuel lines, short bed tank Etc. But one of my main questions is if I did this on flat ground with all tires inflated properly can I trust that cutting the frame and Welding it back together basing not only off measurements but on level a trustworthy technique? This is my project / daily so I really don't want to screw this up.
87 single cab, 2wd, 305 w/ 700r4

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Dang. You're in Fort Polk. I know a junkyard that has a short bed box and frame with fuel tanks, lines, and pretty much everything still on it (IIRC) in Summit, MS. It's about a three and a half hour drive for you each way, but it maybe worth looking into if it's all still there. It's at County Line Auto Sales and Salvage, and the number is (601) 276-7551 if you're interested. They can come off as rude sometimes, but I've been dealing with them for years, and they're just different. There's a guy there named Jerry (I think - been a while) who'll go and check it out for you, tell you what you want to know, probably quote you a price on the whole thing right then, and you can usually haggle with them enough to where it makes a difference. He's honest and friendly, but I don't know how much they'd want. They're usually respectable on square body parts.

 

[bluex]

A straight vertical cut will be plenty strong. I did mine in 2004 with a straight cut in my back yard on a mostly level spot. It came out perfect, the truck drives and tracks straight and I have loaded it down (several times a little to much) plenty of times over the years with no issues. It was welded with a stick welder, allowed to cool and then plated on the inside only. The guy that helped me used to build rollbacks and did moble welding on the side. He said all rollbacks and big trucks were always straight cut and plated. I trusted his judgement then and it hasnt let me down since.

Look up the GM upfitters manual for a cab and chassis truck. If you have to lengthen the frame on those they also recommend a straight cut, just sayin....

 

[bluex]

some pictures...

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[bluex]

I would do a few things differently if I ever did one again. You can measure it out to where the bed bolt holes line back up except for the very back ones I believe. I just cut it and drilled new holes. The important thing is when you line it back up you get it square and level in regards to the front part of the frame before welding it solid. You can compensate then for the ground being slightly unlevel. As far as the measurements its 14" out of the middle and either 5 1/2 or 5 3/4 off the back. I just set the bed on there and cut off what was needed to get it to sit down correctly. I dont remember that exact measurement.

And now I'll sit back and wait on all the experts to tell me how I've built a death trap and it will casue me to murder a family in a minivan because I used a straight cut....


BTW, it went 5 laps around Charlotte Motor Speedway this past weekend as fast I could make it go. I dont have a speedometer due to the NV3500 swap but according to the math i should have been over 120 in the straights....

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[Jrgunn5150]

I would do a few things differently if I ever did one again. You can measure it out to where the bed bolt holes line back up except for the very back ones I believe. I just cut it and drilled new holes. The important thing is when you line it back up you get it square and level in regards to the front part of the frame before welding it solid. You can compensate then for the ground being slightly unlevel. As far as the measurements its 14" out of the middle and either 5 1/2 or 5 3/4 off the back. I just set the bed on there and cut off what was needed to get it to sit down correctly. I dont remember that exact measurement.

And now I'll sit back and wait on all the experts to tell me how I've built a death trap and it will casue me to murder a family in a minivan because I used a straight cut....


BTW, it went 5 laps around Charlotte Motor Speedway this past weekend as fast I could make it go. I dont have a speedometer due to the NV3500 swap but according to the math i should have been over 120 in the straights....

Nah, I agree, straight is fine. But I also wouldn't discourage anyone from getting fancier if they choose to. I've done several straight cuts myself.

Do you have any other info on your 3550 swap or a build thread? I'd like to know more.

 

[bluex]

I wasn't trying to discourage a fancier cut just saying a straight one is plenty strong enough is all.

My build thread is here:

http://www.gmsquarebody.com/threads/78-gmc-forever-build.16379/

NV3500 swap specific thread:

http://www.gmsquarebody.com/threads/nv3500-swap.16360/

 

[MarshMobbin907]

I shortened my longbed frame to a shortbed. Not difficult at all. Just paln ahead and I HIGHLY recommended a vertical to horizontal then back to vertical cut when notching the frame. Dont just cut vertically...it wont be strong enough no matter how its reinforced. Definately do it correctly so everything lines up equally and you get more weld contact. Working on a level surface is key, support the frame with jack stands equally (double check the measurements. I made my frame cuts just behind the front section of the saddle tanks. From memory...I believe that I removed about 12 inches from the original longbed up front and cut a small section off of the back of the frame. I just took measurements from the front of the shortbed to the center of the wheel tubs. I then transfered those measurements to the longbed frame. Why most people are intimidated by doing this....I dont know. Shortbeds, at least here out West are harder to source for a decent price. My main reason for the conversion was that longbeds at least here are abundant and on average go for 1/3 the asking price of shorties. My longbed truck was $2350 running and driving. The shortbox was $135. I sold the longbed which was damaged on the drivers side for $100.......

Shortbed trucks running and driving.....average over $4000.


So I am still ahead of the game and made my truck what I wanted it to be.......at least for now.


And for what its worth...I used a Lincoln 110 volt wire feed that has the capacity to weld a single pass weld for up to 1/4" thick steel. The steel on these squares isnt as thick and robust as most people think. Using a 110v wire feed with gas is fine. Anything else is just plain overkill. If you arent a competent/experienced welder or you would feel better hiring a welder, then go for it. I have been welding tig, stick, mig and acy/oxygen for over a decade. I am confident in my welds and my abilities. I also used a sawzall to make my cuts, using a 1/2" drill bit to drill out the intersecting cuts first. I also welded 3/16" thick steel backing plates on the inside sections of the frame where the "z" cuts had been welded. Some others who have shortened frame like using plasma cutters, but they tend in my opinion to make messier cuts. The smaller the gap to weld, the better and stronger it will be. Accuracy is key...measure three time, cut once.


You will need

shortbed saddle tanks (if you want dual tanks)
Shortbed driveline
cut and shorten the parking brake cable
shorten the rear tail light wiring harness
And.....often overlooked...a shortbed from a donor truck that also has dual saddle tanks (I could not source a shortbed with dual tank doors, so I removed the door from my longbed and grafted it onto the shortbed.)

So i think I'm going to buy a little flux core 130, do you think that would be sufficient if I played the back and boxed the frame? I don't plan on towing much honestly but I just want it to give when going down the road one day.

 

[shiftpro]

So i think I'm going to buy a little flux core 130, do you think that would be sufficient if I played the back and boxed the frame? I don't plan on towing much honestly but I just want it to give when going down the road one day.

You have two professional welders on this thread telling you a little 110 mig is not the tool for the job, and yourself once being a certified 7018 stick welder should KNOW that a toy welder is for welding battery boxes and body panels, not frames.
Here's a good option, get everything ready to weld then call a pro mobile welder to come over and zip up for you. It won't cost much if you do the prep correctly.
And... I sincerely feel for you that you need your wife's permission to buy a welder, just saying.

 

[Honky Kong jr]

So i think I'm going to buy a little flux core 130, do you think that would be sufficient if I played the back and boxed the frame? I don't plan on towing much honestly but I just want it to give when going down the road one day.

Flux core is for making yard animals out of garden tools not welding frames. You want a MIG set up. And I hen welding vertically you go bottom up.

 

[MarshMobbin907]

Where can I buy a cylinder and what gas should I use?