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Old 04-18-2015, 10:09 PM   #1
65standard
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A different approach to a LWB to SWB conversion

Since I needed to pull the bed on my 1970 C20 to do cab corners, I decided to make it a short bed too. My approach is different than the conversions I see most doing on this site. As a metal shaper, we are taught to plan out our cuts and splices to ease fabrication, save time, and avoid frustration later on. So I came up with a better idea to make cuts and seams easier to do and keep the original paint, well most of it. Here is my plan:

Before:



First remove the bed. I just cut all 8 bolts and unplugged the rear harness.



Remove 8" from rear of frame rails and move the slot on top forward too.



Then remove the front most bed mounting bracket.





Then remove the front rivet of the second bracket and swing out of way. Then mark the cut. I went from the front rivet hole of the front bracket to the front rivet hole of the second brackets.



Then I unbolted the trailing arms from the crossmember, removed all rivets from crossmember and slid it forward 12". I welded in place. Then I cut the frame rails.



To be continued...
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1954 Chevy 3100 SWB 392 Hemi 727 torqueflite 4.56 9" Ford
1970 Chevy C/20 SWB L6 4-speed 457 gears
1985 Chevy C/10 SWB 6.0L 4L80 373 locker
1996 Chevy C1500 SWB 5.7 5-speed 3.42 locker
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Old 04-18-2015, 11:41 PM   #2
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Re: A different approach to a LWB to SWB conversion

Interesting.

More than one way to skin a cat.
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Old 04-18-2015, 11:44 PM   #3
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Re: A different approach to a LWB to SWB conversion

I shortened the frame right behind the cab just like you did. The only difference was I put a 2" step notch. Sure makes it easier if you dont want to pull the cab off.
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Old 04-18-2015, 11:53 PM   #4
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Re: A different approach to a LWB to SWB conversion

My cut behind the cab
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Old 04-19-2015, 08:56 AM   #5
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Re: A different approach to a LWB to SWB conversion

Then I carefully aligned the rails and tack welded them together.



Next did a full penn weld and ground it down so it could be tested. Then swung the bed mounts back.





Cut the front drive shaft down, exhaust, and brake line.



Then drove it out to take a look and the new profile.



Next comes the bed...
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1954 Chevy 3100 SWB 392 Hemi 727 torqueflite 4.56 9" Ford
1970 Chevy C/20 SWB L6 4-speed 457 gears
1985 Chevy C/10 SWB 6.0L 4L80 373 locker
1996 Chevy C1500 SWB 5.7 5-speed 3.42 locker
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Old 04-19-2015, 09:04 AM   #6
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Re: A different approach to a LWB to SWB conversion

Nice work... does that frame need any more reinforcement in the weld area? I see a lot of people use a plate behind it.
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Old 04-19-2015, 09:17 AM   #7
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Re: A different approach to a LWB to SWB conversion

Quote:
Originally Posted by 65standard View Post
Then I carefully aligned the rails and tack welded them together.

Next did a full penn weld and ground it down so it could be tested. Then swung the bed mounts back.

Cut the front drive shaft down, exhaust, and brake line.

Then drove it out to take a look and the new profile.

Next comes the bed...

95% of the people that read your thread are not going to have a clue what a penn weld is (including me) and what you mean by being "tested". I did a Google search for "penn weld" and not much came up.

Also wondering if you plated the inside of the frame at all.

Just personal preference I guess, but I would never use a straight cut to shorten a frame.

Thanks,
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Old 04-19-2015, 09:38 AM   #8
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Re: A different approach to a LWB to SWB conversion

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95% of the people that read your thread are not going to have a clue what a penn weld is (including me) and what you mean by being "tested". I did a Google search for "penn weld" and not much came up.

Also wondering if you plated the inside of the frame at all.

Just personal preference I guess, but I would never use a straight cut to shorten a frame.

Thanks,
LockDoc
Full penetration weld. Means there is 100% weld joining the 2 piece of metal instead of just butting the 2 pieces together. You can see he has a slight gap between the frame rails, then he adds a small piece of metal to one side and uses weld to join it together. Hope that helps

Great work btw
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Old 04-19-2015, 09:40 AM   #9
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Re: A different approach to a LWB to SWB conversion

penn weld is a full penetration weld. tested would mean that a certified weld inspector would check the weld for full penetration using some method of testing
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Old 04-19-2015, 09:48 AM   #10
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Re: A different approach to a LWB to SWB conversion

95% of the people will not like my frame since I am not added any fish plate. A full penetration weld is just that, the weld bead is the full thickness of the material. This is done by beveling the rails and leaving a small gap before welding. Once welded, you will have a raised bead on both sides of the rail.

I then ground down the weld so it could be tested. A machine like an ultrasound and jelly is used to look for and air gaps or disturbances in the metal. Also, grinding the weld smooth avoids any stress spots or sharp edges.

If the weld was not 100%, I would add a brake formed channel to fit inside the rail. This is much better than a fish plate or boxing plate.

Now, off to the bed. I completely disassembled the bed and cut down the floor pan. 12" off the front and 7.5" off the rear.



I drilled new front and rear mounting holes in the pan and bolted it to the frame.

You can see it still looks factory.


For the rear, I saved the rear cross sill and put it back on the frame and under the pan.



Then I started to tip over the 1/2" of floor pan I saved when I cut 7.5" off.



Once fully tipped, I plug welded the pan back down to the cross sill. The floor is now a SWB pan and no splicing like all others I have seen here. I saved over 10' of weld and kept my original paint.






Now off to the bed sides....
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1954 Chevy 3100 SWB 392 Hemi 727 torqueflite 4.56 9" Ford
1970 Chevy C/20 SWB L6 4-speed 457 gears
1985 Chevy C/10 SWB 6.0L 4L80 373 locker
1996 Chevy C1500 SWB 5.7 5-speed 3.42 locker
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Old 04-19-2015, 10:09 AM   #11
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Re: A different approach to a LWB to SWB conversion

Interesting. Looking forward to seeing how you do the bed.
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Old 04-19-2015, 10:29 AM   #12
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Re: A different approach to a LWB to SWB conversion

What's your plan for the front of the bed floor where the front bed panel attaches? Will you form all the beads flat where the two bolt together?
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Old 04-19-2015, 10:40 AM   #13
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Re: A different approach to a LWB to SWB conversion

No. I didn't see the need to flatten the pan where the bulk head bolt down. I will just re drill the bolts between the ribs of the pan.

I am aiming to keep as much of the original paint and rust as possible. I do not want two huge weld seam on the sides of the bed. I can't keep the original paint or finish the weld that way. It would surely require bondo and new paint with that cut down method.
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1954 Chevy 3100 SWB 392 Hemi 727 torqueflite 4.56 9" Ford
1970 Chevy C/20 SWB L6 4-speed 457 gears
1985 Chevy C/10 SWB 6.0L 4L80 373 locker
1996 Chevy C1500 SWB 5.7 5-speed 3.42 locker
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Old 04-19-2015, 11:42 AM   #14
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Re: A different approach to a LWB to SWB conversion

I'm pretty much amazed so far. I'm looking forward to the bed work
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Old 04-19-2015, 12:07 PM   #15
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Re: A different approach to a LWB to SWB conversion

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I am aiming to keep as much of the original paint and rust as possible. I do not want two huge weld seam on the sides of the bed. I can't keep the original paint or finish the weld that way. It would surely require bondo and new paint with that cut down method.
How do you plan on shortening the bed sides without weld seams while still retaining a factory short bed appearance?
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Old 04-19-2015, 12:51 PM   #16
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Re: A different approach to a LWB to SWB conversion

For the front of the bed I scribe two lines. My cut line at 11 1/8" and my tipping line at 12". More pictures as I go....
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1954 Chevy 3100 SWB 392 Hemi 727 torqueflite 4.56 9" Ford
1970 Chevy C/20 SWB L6 4-speed 457 gears
1985 Chevy C/10 SWB 6.0L 4L80 373 locker
1996 Chevy C1500 SWB 5.7 5-speed 3.42 locker
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Old 04-19-2015, 01:28 PM   #17
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Re: A different approach to a LWB to SWB conversion

looks like very nice work. waiting for more pics
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Old 04-19-2015, 02:10 PM   #18
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Re: A different approach to a LWB to SWB conversion

Looks great! You work wonders with metal and it sure is fun to watch.
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Old 04-19-2015, 02:51 PM   #19
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Re: A different approach to a LWB to SWB conversion

This is great info for when I shorten mine
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Old 04-19-2015, 02:57 PM   #20
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Re: A different approach to a LWB to SWB conversion

Some good ideas
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Old 04-19-2015, 03:54 PM   #21
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Re: A different approach to a LWB to SWB conversion

Nice
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Old 04-19-2015, 04:21 PM   #22
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Re: A different approach to a LWB to SWB conversion

Looks great.
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Old 04-19-2015, 05:52 PM   #23
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Re: A different approach to a LWB to SWB conversion

The bulkhead will just bolt to the floor pan something like this. I will drill holes on the lows of the pan.



Here are my scribe lines on the front of the bed side. One for cutting and one for tipping over the edge.



I will tip the edge over just like the factory did here.


If I wanted to, I could just weld the bed side back together right at the edge. But I don't want to burn the paint if I don't have to.



Once I cut the extra material off, I started to tip over the inner panel. Again no welding here.



And started to tip over the outer bed skin.



With the inner panel fully tipped, I slid the end cap in place to see my progress.




Test fit is looking good. I just need to complete tipping the outer skin to the end cap, spot weld back together and add the front bed pocket to finish up this corner.


100% of the original paint save and 17' of weld avoided so far.
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1954 Chevy 3100 SWB 392 Hemi 727 torqueflite 4.56 9" Ford
1970 Chevy C/20 SWB L6 4-speed 457 gears
1985 Chevy C/10 SWB 6.0L 4L80 373 locker
1996 Chevy C1500 SWB 5.7 5-speed 3.42 locker
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Old 04-19-2015, 05:59 PM   #24
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Re: A different approach to a LWB to SWB conversion

Damn fine work fella! Nice and original looking
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Old 04-19-2015, 06:01 PM   #25
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Re: A different approach to a LWB to SWB conversion

I'm kind of curious how your frame will do without fish plating it. You have two brittle lines running up your frame. Fish plating spreads that stress over multiple areas. It's not a matter of whether the weld is completely penetrated, it's the stress on the toes of the weld. Without heat treating, those toes will be weaker than the weld or the unheated frame.

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