SWB Conversion Behind Cab?

[slamgears]

69 c10 LWB

Anyone done it? Tips for doing it? Want to SWB convert my truck but don't have the room to take the cab off. I can't find any issue in just doing it behind the cab, making two L shaped cuts, and then welding it together/fish plating it.

Just trying to get second opinions to figure out if it's a good idea or not.

[randy500]

Easy to do behind the cab with leaf springs but the area to weld is tight up against the rear cab mount (the straight part of the frame) and difficult to make sure the cut still retains the frame level when looking along the frame left to right.

Harder with coils because of the same issue and you also have to in-rivet the trailing arm crossmember, slide it forward and re-attach it, 4 of the rivets are on the upper rail which makes re-attachment difficult because the cab is in the way.

Best bet is to raise the cab a foot or more over the frame (if you have room to park it and work on it you have room for raising it), support it on jack stands or something and cut it in the center where its nice and flat.

[slamgears]

Well the trailing arm cross member is coming out anyways and I'm pretty sure I can get to it easily, since the suspension will be off anyways and I think without that there I should be able to reach everything pretty easily to do the cutting/welding right?
I may even ditch the trailing arm member and just make a new piece out of thick square tube right behind the cab, so I keep the rigidity but I can get rid of the stock looking crossmember.

[bs46488]

Your modifications to the cross member sound harder than removing the cab.

With your idea of replacing the crossmember with square tube, would you have to make shorter trailing arms?

Instead of removing the cab, I might try tipping up just the back and gaining some extra working room.

[52napco]

A straight cut will work just fine if you are a good welder... it's not like your going to haul anything heavy lol...I would add a 3/16 or so strip on the bottom I side of the rail.

[slamgears]

Trucks going on bags, sorry forgot to mention that. So no trailing arms at all. Doing a 4 link. I'm a bit skeptical about a straight cut. But without the trailing arm member I should be pretty much good to do the L cuts anyways. I'd rather make it strong as hell than not make it strong enough.

[GASoline71]

https://www.brotherstrucks.com/63-72...tinfo/LTSC372/

Gary

[hewittca]

I just completed a shortbed conversion on my truck by cutting behind the cab. I incorporated a 2.5" step up in my frame when I shortened it, so I had to do it behind the cab due to clearance, but the process would be the same with or without the stepped frame. I have photos and details in my build thread (see signature). I based my conversion on the one done by 65standard here where he does a straight cut on the frame just behind the rear body mount. If you are replacing the crossmember anyway, that is a significant portion of the work that you will be doing regardless of where you cut the frame. To me, cutting and rewelding the frame was actually pretty easy, it was relocating that crossmember that was a PITA.

[slamgears]

Hewittca, thanks man looking at yours makes me feel way better about mine. The straight cut is looking more and more appealing, that way I can just chop 12 inches out where it's straight, and weld it, fishplate it and be done.

But yeah that's the plus side to doing bags, no trailing arms to worry about mounting so I can just get rid of the stock member altogether, and make something to add that rigidity back to the frame.

[slamgears]

My only point of worry in the straight cut was strength, since I know in 65 standard's thread he pointed out C10 frames are thinner than c20 frames, I just don't want it to be too weak.
Opinions?

[52napco]

Has anyone ever.been around structual I beam welding ??? Let me.assure you we don't put a goofy z cut in the I beam ......i just finished a bridge last year spanning 30 feet utilizing 8
22lb per foot I beams and the engineer specified straight cut welds with 1 fish plate.
We are driving dump trucks and propane trucks across it daily.
So trust me.... a straight cut is fine for.this

[slamgears]

Napco that's what I was looking for, appreciate it haha. I'm in software by trade so welding is just a hobby for me, I don't really talk to anybody regularly who does production welding on the daily so I end up asking best practices for welding techniques and stuff on here so that's definitely helpful, and I feel way better doing a straight cut then trying to do a fancy z cut and mate it together

[randy500]

So if your putting a fish plate in cut up the piece you cut out to make the fish plate, you can section it lengthwise and they fit nice with a upper and lower flange

[67 chevelle]

You dont have to take the cab off , but you do have to remove the back 2 cab suports to do it wright , under the cab , and I would do a z cut with radius , lots of threads on this board

[randy500]

Originally Posted by 67 chevelle

You dont have to take the cab off , but you do have to remove the back 2 cab suports to do it wright , under the cab , and I would do a z cut with radius , lots of threads on this board

I was going to add the removal of the cab supports too...you get really close to them and they pretty much are exactly where you need to weld. I did it once to save some time and my weld did get onto the rear cab support, I didn't like that but it did work. Just sloppy.

[tutone]

Originally Posted by GASoline71

https://www.brotherstrucks.com/63-72...tinfo/LTSC372/

Gary

X2 Easiest and safest way in the long run. Especially if you sell in the future. The next guy will feel better knowing he is riding on a frame with a company backed conversion kit under him, at least I would.

[slamgears]

Originally Posted by tutone

X2 Easiest and safest way in the long run. Especially if you sell in the future. The next guy will feel better knowing he is riding on a frame with a company backed conversion kit under him, at least I would.

Yeah they're nice, but I'm not buying any bolt on parts for this build. My goal for the build is to fabricate as much as possible myself for budget reasons and just for fun. I like the full porterbuilt builds with all the bolt on stuff and brothers parts, but I wouldn't feel right unless I did as much as I could myself.
The main plan for the build is budget build but done right. Hopefully when I'm done you won't even be able to tell the frame was welded together.

[tutone]

Ok I will give you that. I am doing the same thing on my 67 LWB and don't have the room as well. I still do not intend to remove the cab, but my cut and weld is going to be under the cab, not behind it. Some one on this board used these frame stiffeners from Early Classic Enterprises and did a nice conversion. I think about 40 bucks or so? Anyway, its the same concept as the Brothers kit, except you don't have somebody holding your hand all the way through, telling you where to drill and cut. If you have enough fabrication skill to cut and weld a frame, then you can use something like this . that is what Im going to do. the down side is relocating your back cab mount.

[bs46488]

Slamgears,

Check out this thread.

http://67-72chevytrucks.com/vboard/s...d.php?t=667694

[randy500]

Originally Posted by bs46488

Slamgears,

Check out this thread.

http://67-72chevytrucks.com/vboard/s...d.php?t=667694

That's a great thread. It does seem to me when I cut one down behind the cab my weld was right on the cab mount, measure it and see where it lands, I bet the lower part of the cut in that thread gets into where the frame kicks up.

Here is a tip I use when cutting one down.

I use a square to scribe my cut lines, I then make another line on each side of the cut, at least one inch further on each side. So lines 12" apart and lines at 14" or so, even numbers. I record the difference.
On the 4 scribe lines I use a sharp center punch and punch marks along the scribed lines, I do this so when I'm grinding or sanding I don't loose my original lines.
Before I weld it I ensure the remaining lines after the cut are parallel by seeing that they are equal distance apart top and bottom. This makes sure the frame is not sagging or bowed up.
I also verify my square is actually square before any work by scribing a line with the short side of the square facing left and right, if the lines don't deviate then the square is true.

If you do this behind the cab you will be fine, you may have some height difference at the bottom of the weld/cut to make up but the frame will be true as it was when you started.

One more thing...use a straightedge on the top of your frame when you start the job to ensure the frame is indeed flat.

[jwn1975]

I did one under the cab but left the cab on. Lifted the rear with a jack. I also used the early classic stiffners. Nobody had a "kit" when I did mine a long time ago.

[Daman]

Originally Posted by GASoline71

https://www.brotherstrucks.com/63-72...tinfo/LTSC372/

Gary

Now that's neat.

[leddzepp]

Originally Posted by tutone

X2 Easiest and safest way in the long run. Especially if you sell in the future. The next guy will feel better knowing he is riding on a frame with a company backed conversion kit under him, at least I would.

X3, make your life easier