'71 F350 motorhome conversion, "Bessie"

[Jacksdad]

With the panels somewhat lining up, I started trimming the cab sheet metal and the donor pieces.

32 Cutting rear panel.jpg

33 Trimming rear sheet metal.jpg

The lower panel was starting to line up nicely now with no appreciable gaps around the edge. When it came to welding it in place, I was planning on butt joints - but with a twist. After cleaning it up, the holes on the right side showed up under a layer of bondo from a previous repair.

34 New sheet metal.jpg

[Jacksdad]

I decided to get the upper panel trimmed to size before welding the lower section in place to avoid locking any misalignment in the cab that would be difficult to fix later. Didn't work out that way in the end, but hey...
The roof relaxed a lot as I was cutting the 90 degree edge off, and some of the more extreme high/low spots came out on their own. It was still not completely straight, but it looked better.

36 Trimming the roof.jpg

37 Cutting upper sheet metal.jpg

38 Sheet metal trial fit.jpg

Lining up the donor panels was made easier by the complex shapes you find on the back of a bump's cab - the pinch weld and multiple contours will only line up one way. I'd also marked the center of each panel before I removed them at the wrecking yard. Everything was going well - or so I thought.


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[Jacksdad]

My first indication that something was amiss was when I noticed that the upper right corner of the rear window opening was way too far back. When I sat the MDF window in place, it didn't come close to sitting against the pinch weld the rubber gasket sits on in that one spot. My window would literally have needed to be curved to fit. It was time for brute force and ignorance...

39 Adjusting window corner.jpg

A screw jack and block of wood between the back of the cab and the closet slowly pushed it back where it needed to be, but I should have taken the distortion as a sign of things to come.

[Ranchero50]

Interesting project, hopefully with a happy ending. You'll enjoy the flat bed, a dump module under it makes it even more useful.

I have a feeling you end up with a replacement cab. It would be simpler vs. trying to fix yours.

[popeyes71]

Great project thread. Trying to straighten sheet metal that has been cut and is distorted can be a real chore. I wish you my best with your project and I'm looking forward to how things turn out!

[Jacksdad]

Thanks guys. I'm at work right now, but I'll post more pics if I can stay awake this evening.
Ranchero - a new cab would have been great before I got too far into this one, but funds didn't allow it unfortunately. Luckily I already had the tools, and enough spare time to work with what I had. It wouldn't be any fun if it was easy, right?
On the plus side, other than the usual rot at the lower edges of the fenders, this cab is essentially rust free. The cab mounts, drip rails and floors are rock solid. I have made more progress than the pictures I've posted so far might suggest - I'll try and get the thread up to date when I can get to the pics on my computer. She's not done yet, but we're getting there slowly.

[Jacksdad]

Once I had the top piece fitting well enough that I felt confident in welding the lower panel in place, I finished bracing the gap with tubing to keep the two sides aligned. I drilled holes through the panels and welded through to the tubing every few inches, and did that along the length of each piece. Here's where the twist I mentioned earlier came in. Whenever I can, I like to reinforce butt welded joints in sheet metal with a backing piece at least as thick as the pieces being joined. Placed behind the panels to be joined and plug welded in place on both sides, it keeps the edges aligned and adds strength without being seen. I welded strips in place all around the edge of the hole left over from the walk through before final welding of the donor panel. If you leave a slight gap and try to burn through to the bracing strip below, it becomes less of a butt weld, and more of a lap weld (if that makes sense).

41 Bracing strip detail.jpg

42 Bracing and tubing detail.jpg

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[Jacksdad]

If you look at the way the back of a bump's cab is constructed, you'll see that the panel below the window is actually a double skinned section that's spot welded together along the line where the gas tank bolts are situated. By drilling through those lower welds, I was able to open it up and drop it over the tubing/bracing pieces. I held the box section closed with new gas tank bolts while I welded all around the edge and through to the tubing underneath, then redid the spot welds by filling the holes left when they were drilled out. I decided to tack the edges of the bracing pieces to tie it all together a little more as well. Hey, I was bored and I had wire and gas...

44 Rear panel welded inside.jpg

43 Rear panel welded.jpg

45 Inside cab primered.jpg

[Jacksdad]

After grinding the welds down, I was pleasantly surprised at how straight it had all come out. It shouldn't take too much tweaking to get it ready for paint.

46 Rear panel welds smoothed.jpg

47 rear panel primered.jpg

With the lower panel in place, I turned my attention to the section above the rear window thinking my issues with distortion were over. Poor naive fool...

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[Jacksdad]

I decided to use the spot welded seam that runs across the back of the cab about 3-4" above the rear window as the guide for the tubing that bridged the gap. I bent it to follow the same line, and welded it in place under the pinch weld on both sides of the gap. I also made sure it was right behind the sheet metal so I could plug weld through for additional strength. Using the same technique as the lower panel, I welded bracing strips behind the join everywhere the two panels came together. Holes punched in the new sheet metal allowed me to weld through to the strip behind after it was in the right position.

48 Upper sheet metal bracing right.jpg

49 Upper sheet metal bracing left.jpg

50 Upper sheet metal prep.jpg

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[Jacksdad]

With the upper section finally in place and the welds ground down, I was feeling pretty good about the way the cab was progressing.

51 Upper sheetmetal welded.jpg

52 Upper sheet metal welded.jpg

When I looked at the rear window opening through the windshield however, I noticed something was a little off. It wasn't much, but the passenger side was slightly lower than the driver's side. Now the distortion I'd seen earlier started to make sense. The framing in the camper box on the passenger side was in bad shape, and I knew some of the wood had been eaten away by an ant's nest I'd found in the roof above the closet. The structure around the door on that side was particularly bad, and I figured it must settled over time and transferred some of the weight of the camper box and cab-over sleeping area onto the passenger side. Missing as much sheet metal as it was, there wasn't much to stop that area being compressed by the quarter of an inch I was seeing, and pushing the corner of the window opening back. Lacking another bump to get measurements from, it was the only explanation that made sense given that all the contours, body lines and seams were lining up perfectly between the original and donor sheet metal. Now I had a decision to make - to go with my hunch that it was the passenger side that was low, and not the driver's side too high. I bit the bullet and decided to raise it.
I figured that the only feasible way to get the window opening square again was to cut through the back of the cab and add some metal. Time to break out the saw

[popeyes71]

Just when it sounded like things were going to be fine, there was a challenge waiting for you right around the corner.

[Jacksdad]

Isn't that the truth
I'll post more pics later, but the old girl certainly hasn't made things easy. I should have the build up to date for you guys soon, then hopefully I can get back into it and start getting my hands dirty again. I really want to have the camper box torn down and a flat bed on her this year.

[Jacksdad]

I cut through the pillar almost to the door opening both inside and outside the cab, and enlisted the help of my trusty screw jack again. The inner panel was a little more complex and required a few more cuts to allow it to expand. It didn't take much for the jack to get everything square and even again, and because it was only a quarter of an inch at it's widest, it didn't mess with the door opening at all - the panels (inside and outside the cab) were able to accommodate the small change in angle necessary without too much drama. I was able to reach up inside and place shaped patch panels behind the gaps, and spot/seam weld them in from the outside to build the strength back into the pillar. I took the opportunity to weld up the gas filler hole on the passenger side at the same time.

99 Roof pillar cut 2.jpg

97 Inner panel cuts.jpg

98 Passenger pillar before.jpg

[Jacksdad]

Back to the same point I thought I was before. Ho hum. Slight bump in the road (sorry...), but I'm glad I fixed it. Whether or not it would have affected fitment of the rear window, it would have bugged the hell out of to see the misalignment between the top edge of the front and rear windows. After I was all done with this repair, I did get the chance to pop the rear window out of a bump in the wrecking yard and it was within a millimeter of mine at every point I measured, so I'm happy.

Passenger pillar after.jpg

55 Inner cab repaired.3.jpg

60 Correct window opening.jpg