I've done a search but can find nothing on this. I guess it depends on what search terms one uses.

I have a '74 4 X 4 crew cab, sans short box. As far as I am aware there were no long box 4 Xs made in the '70s. What I want to do is install a 2 X 4 long box on my 4 X 4 which will nessesitate the cutting of the frame just behind the cab and welding in 18 inches of frame material. I have the box and the frame pieces plus extra 1/4 plate for fish plating the joints and hiding the fact that it's been modded. I know to avoid 90 deg. cuts and to plate a minimum of 12 inches either side of the cut. I also plan to weld and bolt the plates, and not to weld the plates solid but to leave
small areas unwelded to avoid new stress risers.

Went to the local fabrication shops and found that the price for the job is some where between $800 and $1100 clams, plus taxes etc.

I would like to do the job myself. I am a competant welder and have fabricated lots over the years but what I would like to know is, has anyone here ever done this, and if so, do you have any tips for me that could save me some trouble in the long run?

Cheers

 

I was advised not to weld the crack in my frame rail as the steel is heat-treated and would, in all likelyhood, just develop a new crack at the edge of the weld. Instead I fabricated an inner and outer "C" section and sandwiched the crack with this bolted-to brace. So far, so good. This is not gospel.... just food for thought.

 

Mut,
I knew a guy in North Carolina that did this from time to time.
He used to cut the frame in an "offset", that being, the left rail was cut further forward than the right. He claimed that this would elimnate the specific stress on any given side or both welds at the same time.?
1. Get a frame from a long bed truck.
2. Cut it offset and cut your truck frame offset to match.
3. Weld 'em together.
What kind of welder were you planning on?
KingFisher
PS I maybe the worst welder in the world. I just started last week. I always had the greatest respect for welders, now I envy them as well.

 

Thanks guys for the thoughts on my project. Offsetting the cuts was some thing I had not thought of, although there isn't much room to offset I'll give it the ol' eyball and see.

My welder is a 160 amp mig, but I have access to my father-in-laws 300 amp AC/DC stick welder as well, (he owns a wrecking yard). Now you know why I married his daughter

For this project I could really use a good plasma cutter, but some thing like that is a bit past my budget. Anyone have one they'd like to donate?

The only long frames for crew cabs in those years (as far as I know) are the 2 X 4 ones, and if I used one (I have three), I'd have to alter the front of the frame for a 4 X 4 front end which is a bigger deal than modding the rear of the 4 X 4 frame.

As far as fishplating the frame, I won't stay to the minimum of 12 inches per side of the weld. I will go as far as I can in either direction, both on the outside and inside . I figure this won't add too much weight as opposed to the strength it adds.

There's a local guy who does drive shaft alteration in his home shop at really reasonable prices. Apart from that I don't know if there's any thing else I should look into.

By the time I've added a rear step bumper and a front winch bumper and bush bars, the total length will be about 23 feet. Parking at the local mall for shopping should be interesting.

Cheers 'n' beers

 

Mut,
I'd use a Sawsall for cutting the frame and some patience.
I think a stick welder may give you what you need to put that frame back together.
As far as the "Fishplate"? I would recommend using a "Glove".
If your really worried, extending down the frame won't help. The plate you use to strengthen may extend off the bottom of the frame. This will give you considerably much more strength.
The stress in a frame occurs at the top and bottom of the rail. By increasing the "height" of the rail, you'll strengthen the loading capability of the rail the most.
Make Sense?
KingFisher

 

There's good metal in a '74, so don't worry much about failure of the parent metal. Use steel rectangular (box) tubing, 3/16" wall thickness if you can. This will take care of both the flex and the strength. Use 7018 low hydrogen rods, which are clean and have been kept dry. Clean, clean and clean the metal before welding. Cut the frame with a torch if you want to - won't hurt a thing. Then clean, clean, clean the metal again. (Can't stress that enough). Be sure you ground your welder directly to your work. Tac a few places and move around, don't magnatize the metal by welding in place all at once. Level, plumb, square, then check it again. Don't worry about weakness - I have done this on two log trucks and a couple of pickups - no one has complained yet and these were truly off-road, rough country rides.

 

Mut,
Im a welder with the Navy Seabee's, not the best welder I might add, but I can get the job done.. I agree 100% with Big Orn execpt I would use a saws-all or a plasma cutter if you can get your hands on one, that way you would have a nice clean cut. Also like he said clean, clean, clean cant stress it enough. Thats probably the biggest problems people have when welding they dont clean before they weld and then the dont chip the slag and the covering that forms over the weld. If you dont get that cleaned good it WILL rust... So Clean, Clean, Clean.. Good luck And fill us in on how it goes...

 

Thanks again for the great input

Clean I understand, oh yes I do. no worries there. I'll sandblast the whole areas to work on first and then grind the weld areas.

I see what you mean dfisher1 about extending the deapth of the frame for strength. Only thing is, it will be noticable to any inspection. Thus the reason for the extra long fishplate extensions, so it won't be noticable. I'll taper the fishplate ends too.

Now boxing it in sound good. It seems to me that will double the strength of the frame in the boxed area, but will that transfer any stress to the ends of the boxing to create problems there?

What about as well as the main box, welding in short boxed sections either side of the main box to disipate stress, like a six inch box every foot?

Cheers

 

No, you don't need additional strength. Remember - the weld area, if done properly, will be stronger than the rest of the frame. Just weld 100% filet weld all the way around the cut frame areas - no gussets, no diamond plates, no fish-plates (except if you want it for cosmetics). Just make sure you get that whole area welded. Those two areas each side (the 12" overlap) will be more than enough for strength and flex.

 

All,
I would have to agree with Big. If the original frame was strong enough, by design, then you only are taking unneccessary chances welding all sorts of crap all over your frame. Frame flexibility is just important as frame strength. The "Glove" technique is used by "Big Three Manufacturers" when frame failures are found after production release. A straight solid weld should be sufficient.
KingFisher

 

Big Orn and dfisher1 thanks, you've just made my job a lot easier.

Now how about sectioning the front frame area and adding enough to install a big Volvo deisel a guy I know has for sale?



cheers

 

Can you say Euclid? Y-O-O-K-L-I-D. Euclid. Yep, try one of those first, might be less of a headache.