Muscletang needs new floor pans - advice?

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The last pic is really hard to see. but if its a seam in the panels coming open then you will want to clean it up and try to pull it together with a c-clamp or self tapping screw if possible, then weld it shut and grind it to look nice. good luck!!!
Thanks for your responses. Here is a close-up but still not easy to see. It does not seem like coming apart. It just looks like the two panels were welded a bit a part. Teh gap is fairly consistent. It looks original or nicely redone. I just don't know if this is normal. I can try to add sealant and then close the gap with a clamp. If it is original welding it shut may not be the proper way.

Actually, some water comes through this hole while driving because the inside plastic panel had some water splash marks. Speculating, that could explain the rust. If water came up through there during driving the area may have stayed wet causing rust over time. It is weird that the car appears in such a good shape everywhere except these floor pans.
If you can see that seam under the car. Check it out and make sure the spot weld look good and did not come apart. If they look good and that's factory then clean it up and fill the seam with seam sealer. But you are right seems like a pretty wide gap.?? You can always clean it up and add some weld to it to ensure it wont open any more then seam seal it to keep the weather out. Hard to say without seeing this kinda stuff in person.

 
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Actually, some water comes through this hole while driving because the inside plastic panel had some water splash marks. Speculating, that could explain the rust. If water came up through there during driving the area may have stayed wet causing rust over time. It is weird that the car appears in such a good shape everywhere except these floor pans.
Tony, I'll snap some photos of this joint on my '72 parts car and the '71.

-Kurt

 
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I was out of town early in the week so finally had some time to grind and clean a little more. Tons of bondo to clean. I am finding out that the rear driver's floor pan was replaced at some point. They used tons of bondo and a terrible welding job. The pan is welded on top of the seat riser.

Please look at the pictures and please advise on what's the best way to cut the welds around the floor pan. I guess some of them I can cut with the cutting wheel but it will be a challenge, specially in the area shown in the last picture where the panel is welded to the tunnel. Crazy!

Picture 1: driver's rear floor pan edge against seat riser

Picture 2: seat riser edge against tunnel

Picture 3: driver's rear floor pan edge against tunnel

Edit: I may have answered my last question. Looking at the replacement pans it looks like they go high up the tunnel so I may have to cut the tunnel just above the weld.

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If your putting in full length pans on both sides, just cut out the old pans and seat risers. If they overlapped the seat riser it may be pretty difficult to get them apart. But it would be easier to try to separate them on your work bench. If you cant get them apart just bite the bullet and buy the new seat risers and cut them down to fit you. Its not too hard to do and you can cut them as much or as little as you like to get a custom fit for yourself. I left my replacement passenger side seat riser alone because my wife is pretty short and it helped her see over the dash and hood. I only modified the drivers seat riser. Hope this helps some.

 
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If your putting in full length pans on both sides, just cut out the old pans and seat risers. If they overlapped the seat riser it may be pretty difficult to get them apart. But it would be easier to try to separate them on your work bench. If you cant get them apart just bite the bullet and buy the new seat risers and cut them down to fit you. Its not too hard to do and you can cut them as much or as little as you like to get a custom fit for yourself. I left my replacement passenger side seat riser alone because my wife is pretty short and it helped her see over the dash and hood. I only modified the drivers seat riser. Hope this helps some.
So if I understand correctly, the modification of the new riser will require to cut the vertical sheet metal and then reweld, correct? Anything else?

Is there a writeup thread for this? I looked but may have to try again.

Thanks.

1971 M-code Mach 1

 
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If your putting in full length pans on both sides, just cut out the old pans and seat risers. If they overlapped the seat riser it may be pretty difficult to get them apart. But it would be easier to try to separate them on your work bench. If you cant get them apart just bite the bullet and buy the new seat risers and cut them down to fit you. Its not too hard to do and you can cut them as much or as little as you like to get a custom fit for yourself. I left my replacement passenger side seat riser alone because my wife is pretty short and it helped her see over the dash and hood. I only modified the drivers seat riser. Hope this helps some.
So if I understand correctly, the modification of the new riser will require to cut the vertical sheet metal and then reweld, correct? Anything else?

Is there a writeup thread for this? I looked but may have to try again.

Thanks.

1971 M-code Mach 1
The vertical is too tall on the new seat riser. All I did was cut it down to the height I wanted then welded it down to the floor pan with a few 1 " stitch welds around the perimeter. Once I cut the riser down I lost the bottom 90 degree flange that you would usually plug weld down. You can always take the time to weld the flange back on, but I didn't think it was necessary. If welded properly, that riser isn't going anywhere when you are done! It takes some trimming and grinding to get it to fit perfect, but nothing too crazy. Just take your time. I also moved mine back about 2-3 inches for a little more leg room while driving.

 
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Just take your time. I also moved mine back about 2-3 inches for a little more leg room while driving.

+1 on the moved back 2-3 inches. Did the same thing and I am so glad that I did!

Nothing like lounging in the back seat while driving the car!

Seriously though, the extra couple of clicks made a huge difference in stretching out.

Something to consider.

 
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Nothing constructive to add, but I always enjoy the thrill of discovering new things about my cars. Sometimes there are happy discoveries, sometimes not so much.

At least yours were welded in. The previous owner of my car filled in every crevice with expanding foam and then pop riveted aluminum sheet over the rust. With lots of RTV. Go figure...

 
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If your putting in full length pans on both sides, just cut out the old pans and seat risers. If they overlapped the seat riser it may be pretty difficult to get them apart. But it would be easier to try to separate them on your work bench. If you cant get them apart just bite the bullet and buy the new seat risers and cut them down to fit you. Its not too hard to do and you can cut them as much or as little as you like to get a custom fit for yourself. I left my replacement passenger side seat riser alone because my wife is pretty short and it helped her see over the dash and hood. I only modified the drivers seat riser. Hope this helps some.
So if I understand correctly, the modification of the new riser will require to cut the vertical sheet metal and then reweld, correct? Anything else?

Is there a writeup thread for this? I looked but may have to try again.

Thanks.

1971 M-code Mach 1
The vertical is too tall on the new seat riser. All I did was cut it down to the height I wanted then welded it down to the floor pan with a few 1 " stitch welds around the perimeter. Once I cut the riser down I lost the bottom 90 degree flange that you would usually plug weld down. You can always take the time to weld the flange back on, but I didn't think it was necessary. If welded properly, that riser isn't going anywhere when you are done! It takes some trimming and grinding to get it to fit perfect, but nothing too crazy. Just take your time. I also moved mine back about 2-3 inches for a little more leg room while driving.
From what I read the new risers sit about 1/2" taller, is this the case? If so, may not matter since I am 5'8".

 
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From what I read the new risers sit about 1/2" taller, is this the case? If so, may not matter since I am 5'8".
The '71-73s were built around a 5' 10" person (or so I've heard), so you may be OK with the coupe platforms, especially if you feel too low in the car as it is now.

I'm 5' 10" myself, and I wouldn't touch a thing. But then again...it was designed for someone 5' 10"...so...

-Kurt

 
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If I remember right,they are more than a 1/2" taller. But not 100% sure. Order one for driver side and set it in there with the seat and try it out. See how it feels. I am just over 6' tall and my head was rubbing the roof. I had to slouch down when driving until I cut them down to fit me. Also if you have new seat cushions and covers it really magnifies the problem by raising you up even more.

 
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Does anyone knows or can measure the distance from the floor to the seat screw hole (rear hole) of a coupe or convertible seat platform?


Also, would anyone know if a seat platform of a 70 would fit? or at least be of similar height? the screw holes for the seats are all on top, but these can be modified to fit. I wonder if the holes are located in similar locations. Is anyone familiar with the 70's seat brackets compared to the 71-73?

 
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Well, after a long holidays break I am finally back working in the car. Today I think I won the first of many battles. I was able to get the driver's side seat riser out. The rear edge had the rear floor pan welded on top. I was able to take it out with little damage. The front edge is badly rusted, but the rear edge is not terrible. I decided to save this one so I will clean out all the surface rust and redo the front edge. In any case, I needed to rework a new one so I will try to save my current one.


BTW, a tool that was very useful was a seam buster. I got this one from Amazon, http://www.amazon.com/Lisle-51900-Spot-Weld-Chisel/dp/B000BQXBJK/ref=sr_1_3?ie=UTF8&qid=1420953243&sr=8-3&keywords=seam+buster

I highly recommend this tool since it makes the separation of spot welded panels a lot easier. I tried with a regular chisel for a while and it does the job, but it takes more work and you end of bending the seams a lot more that with the seam buster.

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So making some progress. Last night I finish taking out the driver's side floor panel. Now I am seeking advice for the next step.

At Front by the firewall. As you can see in the picture I cut out around the rusted area trying to keep as much of the original sheet metal as possible. The solid black line represents the edge of the replacement pan. My question here is, should I install the new pan as is with a big overlap by spot welding at the edges of the cutout and then welding at the seam; or should I cut the new pan to match the cutout I did of the floor. The later seems to be a lot of work, but I am open to hear suggestions.

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At the rear. The solid line represents the edge of the new floor pan. For this one, I think I will cut out the overlapping area of the replacement pan back to the curve where it goes vertical (right side of picture).

On the left side of the picture the new pan won't cover all the rusted area that I still need to cut out, so here I will have to add couple more pieces of sheet metal. My plan is to try replicating the curvature of this piece by hammering the new sheet metal over the old before cutting the rusted area. Thoughts? I don't have any other means of curving sheet metal that I know of.

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Along the area where the seat riser or platform is. I cut the rusted floor a little below the lower edge of the platform giving me enough for a 1" overlap. I am thinking of cutting the replacement pan to sit just under the platform. Is this a good idea?

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I just did this in my car, and in hind sight, if I were to do it again, I would only use what you have to to replace floor pans. I left about 1/16" overlap at the tranny tunnel and butt welded in the actual floor, and back by the torque box I tried to butt weld until I got to the overlap area of the torque box. My metal was good up there but figured it would be easier to replace what the new pan provided, but in retrospect I think I would only replace what I had to as I think it will look cleaner. But I am by no means a body expert, maybe somebody will chime in with a better answer. my 2 cents. Good luck, its a nasty job!!

 
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If you don't want to be able to tell you replaced the pan from looking up from underneath then you definitely have to butt weld it. Its tough for a beginner. I fitted mine really close all the way around then used self taping screws to hold it tight in place. Then used a body saw or you can use a grinder with cutoff wheel, and cut through both panels. That way they matched up perfect. Butt weld ,then grind down so you cant see it. Up front I butt welded mine till I cam to the frame. I then overlapped the frame and torque box and plug welded it all along the frame, the edges of the pan and a few spots around/on the torque box. Same with the back. If you are having trouble back there you can always leave 3/4" over lap and plug weld it. You can actually over lap and plug weld the entire pan in if you want, and don't mind being able to see the seam from underneath. Just remember to use good seam sealer when finished. Theres no need, I don't think, to weld it solid all the way around the perimeter if you are doing a lap joint. Just space out your plug welds about every inch or so and make sure the panels are nice and tight together. This is where the self tapping screws help. If you have a little gap, run a screw in to pull the panels nice and tight, then burn in the plug welds on each side of the screw. Pull the screw out, then weld the hole of the screw. Looks like your pretty close to being ready. Just take your time and sneak up on your final cut. If I overlap the joint, I fit the floor pan nice and tight, make sure its sitting down on the frame and not being held up by anything and then zip a few screws into it. Once your happy with the fit, then trace around your floor pan for the final time. Once you have a good mark, unscrew the panel and remove it. Now take some 3/4" wide masking tape and follow your outline all the way around. Now you can cut on the bottom of the masking tape and have a nice 3/4" overlap all the way around. there are a lot of different ways to do this stuff. This is how I usually do it, others may differ. If you have any other questions let me know. And GOOD LUCK!!! Keep the pics coming!

 
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Thank you for the insight Kevin. How can I seal the seam from underneath in the area that the floor overlaps the torque box? I was planing on using seam sealer at the lap joint on the edges above and underneath the floors.

 
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And, Do not forget the SEM Products Copperweld Weld-Through Primer 40783.

Eliminate the corrosion that forms between welded substrates with SEM Products Copperweld weld-through primer! This copper-enriched formula has excellent adhesion. Copperweld weld-through primer provides superior conductive properties that minimize the heat zone, reducing distortion and welding spatter.

http://www.summitracing.com/parts/smm-40783?seid=srese1&gclid=CP6P1sTY2sMCFWRk7AodMyMA3g

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