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Rear deck structural questions...


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I'm well into the stitch welding prep right now. What a bitch!!! Anyhow I stripped off all the rubber sound deadener on the rear deck yesterday (air chisel pops it right off, just need to clean the residue off).

 

When I got the rubber off and it looks like the early 240s have a single piece of sheet metal that lays flat where the later Z's have the compartments. This piece is spot welded to the deck just forward of the strut towers, and it has a little lip that is spot welded to the vertical piece behind the seats. My plan is to stitch the seam in front of the strut towers, and also where it hits the vertical piece, and also along the sides if possible.

 

Warning to anyone wanting to do this: It's a bigger job than it looks. And I was pulling off some BEAUTIFUL welds on my struts and crossmember, etc. Welding this sheet metal is humbling... :oops:

 

Questions:

 

1. I've seen people weld up the 4 big rectangular holes in the vertical panel behind the seats. Am I correct in thinking that there is a bit of stiffness to be gained there?

 

2. The swiss cheese holes in the deck... I wouldn't think that they are a problem. I was planning on not worrying about them. Good idea? Should something be done about that area?

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IMO welding the holes closed should gain a bit of strength, although I dont know from personal expirience. As for the sheet metal welding, I hear you man; it's a PITA!!! I have found that when working with old thin body metal, it's almost imposible to weld a 'bead' down without blowing through. What I do is basicaly a series of 'tacks' with each one laid partiallly over the last one. I use a little 110A Lincoln set as low (A setting for heat, and about 1.5 for wire speed) and it works pretty good for sheet metal/body steel. Sometimes you can run a small bead for a 1/4" or so, but then you have to stop for a sec and let the metal cool down a bit. The other thing I've found is if two pieces you're trying to weld arn't sitting as close as possible (even a 1/32" gap can cause problems.. :evil: ask me how I know..) , it blows through one of them instead of welding...

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That area would seem to be fairly stressed, what with the inner suspension arm pivot points, diff mount, lack of overhead strength and the intersection with the transmission tunnel.

 

If I was doing mine again I'd look very closely at what could be done to beef it up a bit around there. Maybe a piece of square tubing running between the wheel arches and tied in everywhere? Be interested to see what you come up with Jon.

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Richard I think you might be a little disappointed. I decided just to stitch weld that panel.

 

Datsunlover, thank you man!!! I went to weld the top section of that panel today and there were some pretty big gaps. I used the air hammer again with a flat tip to beat the edge down, and welded it up. MUCH BETTER! I think the tiny gaps I was dealing with were what was screwing me up before.

 

Still this job is going to end up taking 4 or 5 times as long as I expected. :(

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Cool man, glad I could help out! :) Sometimes it helps to use a tool to hold thw pieces together.. I've heard it called a 'pressbrake' but I don't know the 'proper' term is.. Basicaly, an old tire wrench with an extra piece of bar/whatever welded on the end with the socket. Hard to explain here.. hmmm.. Basically, the end with the 45 degree bend (with the socket) has another piece welded off it, and wraped with tape/foam. the other end, with the big flat screwdriver end can be used to hold or press against the metal. You can push using your arm/shoulder, leg, foot.. head.. whatever.. Looks like this sort of..

 

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Pretty easy to build, and its like having a third hand to help out sometimes! I also find it helps to weld an inch or so, and then hamer/beat down the metal again before continuing to weld. The heat warps the metal, and does strange things sometimes. Oh and the time factor.. did you forget to times the estimated time by 3? :lol: Good luck man, sounds like your havin fun!

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Another thing that helps out sometimes is right when you quit welding, take a ball peen hammer and tap down the metal right ahead of the weld, where you'll be welding next; it has some heat in it from the weld and won't spring back, thus closing the gap even more. This works best when you're doing the 1/4" at a time deal.

 

John

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