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Zaspen

240z floor pan replacement question

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I'm going to replace the floors in my 240 over the winter and I've read as many old posts on the topic as I can find.  After all that reading I can't figure out if it is better for me to attempt a butt weld or overlap a bit and weld a lap joint on the inside of the car.  I'm a novice welder and while I plan to practice a ton before I start I don't want to take on a butt joint if I have little chance of success.  I'm also wondering if I do a lap joint do I just weld on the inside of the car?  Do I then fill the seam under the car with a seam sealer?  How far should I overlap the new pan with the old metal?  I'm looking to get the ZF pans and rails.  Any thoughts/comments are appreciated,  Thanks!

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If you are a novice welder I would go with a lap weld and weld on both inside and underneath then seam sealer on both sides. 1/2" is plenty of overlap and you can use a zip screw (self tapping) to hold it all together, complete all your welds then remove zip screws and plug weld the holes. By the time you get to the end of the welding part of the resto you won't feel like a novice anymore. Are you using a wire feed Mig with gas or flux core?

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Grannyknot has good advise, but I would suggest butt welding them in.

If you have a good gas shielded welder (plenty of Duty Cycle), half the battle is getting it set up properly. You will have it figured out long before you get part way around a panel. If you practice a little first, I think you'll be ok. You can always post some pictures of your first spot welds and we can help you get dialed in.

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I'll be using a gas shielded mig. If I butt weld and my welds have pinholes will seam sealer make everything Waterproof? 

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9 minutes ago, Zaspen said:

I'll be using a gas shielded mig. If I butt weld and my welds have pinholes will seam sealer make everything Waterproof? 

Yes, or you can smear a coat of tiger hair fiberglass to seal the pinholes and smooth it up, don't use bondo. As long as the welds are solid and look good, you should be fine. Weld in short little sections and take lots of time between sets, to reduce warpage. You should consider a good respirator for under your welding hood. Some of that stuff isn't good for you when it burns!

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I've started my floor pan project and I have three questions about fit.  I have the Zedd Findings pans. 

 

1.  It is doesn't fit around the tunnel where the transmission mount bracket is.  I beat it a bit with a hammer but I'm thinking I may need to cut a slot there.  Is this normal?

2.  It seems like the pan is not centered quite right.  If I have the outer lip (opposite tunnel) in the correct location the support rail "bump" in the pans is not centered with the existing rail.

3.  I left about 3" of the old support rail.  It seems like the old pans may have been curved up at the front because only the front lip of the pan contacts the rail and there is big gap at the back.

I uploaded some pictures that show the rail issues.

20181216_130559.jpg

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Pan not centered

 

20181216_130657.jpg

Curved floor pans?

 

Any thoughts would be appreciated!! 

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The panels are a rough fit. Some massaging is required. At least you have a 240 as the 280 pans are way out of fit.

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Looks like you have everything nicely prepped, after you get the pan roughly shaped and placed you can start with the rocker side of the pan and run a couple of zip screws or clecos to hold it, then 1 on the back lip. At the front where you left 3" of the existing support rail you want to force the new pan down into that curve and secure that with a couple of zip screws until you start welding. The position of the pan may change so don't tack weld anything, any holes from the screws can be welded up at the last step.

Now comes the fun part, matching the new pan up to the trans tunnel, there a couple of ways to do it but I like to start in the center close to where the front of the seat would be and secure that with a zip screw then cut relief lines in the pan as you need them to get the pan to lay against the tunnel.  Much twisting and bending of the pan and some stretching of the tunnel will get you there.

If you are lapping the weld joint try and get the lap down to a 1/4" to 1/2", if butt welding leave your lap nice and wide so you can slice down the center of it, try and find the thinnest cutoff wheel you can for that cut, trying to butt weld over a large gap is so frustrating.

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Thanks for all the tips.  The one thing that stalled me the most today was the fact that it seems like the pan was made to "low".  If I line the top of the pan's rocker flange with the top of the original weld surface then the bottom of the pan is about 3/8 of an inch below where the rail is and then the pan has to bend up to reach the rail. I'm compensating by cheating the flange up about 1/4".  It bugs me because it doesn't seem correct.

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Flange part way up "C" channel on rocker

20181216_194951.jpg

Bottom of rocker side of the pan is part way up the original weld surface but yet the pan has to bend up to get to the rail.  Is this normal?

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The pan incorporates an amount of extra material around the edges for you to blend in the panel. You will need to find the best overall fit for the pan, then fabricate whatever you need to make it work.
I made corners and sections as needed.
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This is why butt welding gets tricky. Unless things are lined up perfect you can find yourself patching in gaps . I would recommend Cleco’s - you’ll wonder how you did without them. 

I learned my lesson with these panels - only cut off what’s bad on the original panels. Removing all of the old panel all the way to the inner rocker panel is usually not necessary , usually not much rust all the way up there anyway. I didn’t hardly catch this issue when I did mine. It made the floor slightly off level 

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1 hour ago, Zaspen said:

Bottom of rocker side of the pan is part way up the original weld surface but yet the pan has to bend up to get to the rail.  Is this normal?

Try and think of the pans as only 90% correct, you have to make the pan fit your car,  if you think you don't need that extra 3/8" on the rocker side of the pan and you still have enough work with, cut it off.  Measure twice cut once😉  Did you keep the original floor pan, you can solve a lot of problems by having a look at the old stuff if you still have it.

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I like the 90% thought! I guess I just need to be creative and not expect perfection.  Thanks for all the replies.

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Cleco’s are a great way to get things lined up before cutting thru for the butt weld. The zip disc leaves a nice 1/16” gap to weld into.
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On the passenger side I only used 3/4 of the floor pan and kept the tunnel curve section as it was good.

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Is the general thought to get the pans in then fab and install the firewall patch panels or the other way around?

 

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6 hours ago, Zaspen said:

I hope mine looks that good! 

He illustrated the technique well. Copy what he did. Take you time. Get some dollies and hammers, cheap ones will work. With a good welder you'll be fine. 🖕

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