1970 FB Toe Board Hole Repair

[TomM 25]

My pass side toe board has some thru-rust, looking for advice on planning a repair (pic is shown with a dime).  The rest of the pan looks pretty good as it was an AZ car.  This is a father/son project, meaning:

1) I'm not interested in concourse but I don't want a harry-homeowner repair either

2) I would prefer to perform the repair ourselves

The POR-15 Floor Pan repair kit gets great reviews, I think it contains a fiberglass matt. 

I do have a 110v Hobart gasless mig, I haven't used it much but it is an option.  I could replace the pan section in that area.  The CJPP pan doesn't get great reviews for the 69/70 as the grooves don't match and it turns out to be a cut to fit item.

I realize replacing the sheetmetal is the ideal route.  Thoughts?

Thanks, Tom

[RPM 1,190]

I'd replace the toe board section with NPD metal and mig welded. Practice with some 19ga coupons on your plug and butt welds.

[Ridge Runner 1,112]

Dont use fiberglass to repair the rot ,metal and fiberglass really do not mix well and it will sooner or later peel .i would do the metal patch, it will be worth the extra trouble in the end

[MAC390 327]

Definitely a metal repair then use the por 15

[barnett468 418]

i would first remove the rust so you see exact;y what is good and what is bad. it looks like you might be able to eventually cut it around 1/4" in front of the ribs if it is not heavily rusted there. if that's the case, it will make it a lot easier.

you can but 12" x 12' pieces of flat thin sheet metal at home depot and maybe lowes etc.

just in front of the ribs are spot welds that you will need to drill out . you can but a spot weld remover which will make it a bit cleaner.

you can probably just cut the new metal to the size you need then conform it to fit the floor then draw a line on the outside of it onto the floor then cut along this line. then put the new metal in the hole and put a few tack welds on it to start with.

[jmlay 80]

I think your going to find the rust through is mush larger that you think. As stated get  all of the rust and start poking around with a pick of screw driver to see what it thin and needs to be replaced. Do it once and not need to go back in a few years and do it again.

[aslanefe 333]

I would check the cowl too. If you have a leaking cowl, floor board will rust again.

[TomM 25]

All, thanks for the responses.  Here's a better pic.  I's say the rust extends about 6" up the toe board, especially in the rib on the right hand side (outboard).  The spot welded seam is pretty solid, but behind it on the floor and above it on the right toe board rib are the areas needing attention.  I will look into the spot weld remover, new sheet metal and gas setup for my mig.  Is anyone reproducing the 69/70 sheet metal or should I plan on modifying the 65-70 pans?  If I remove the front portion of the floor pan and up to 6"-8" of the toe board, are there still spot welds that need to be removed or will I have cut them out?  I'm assuming it's better to replace the full width as best I can rather than, say just the RHS rib on the toe board.  Thanks, Tom

[barnett468 418]

the angled part is spot welded at the top edge and on the right side.

there are spot welds anywhere there is a seam where the metal overlaps also

[Ridge Runner 1,112]

If it is like mine there is spot welds on top of spot welds

[TomM 25]

Here's my new pan from CJPP.  I've been reading up on the great debate of lap joints vs butt joints.  We'll spend the next week or so practicing both methods, and see how the butt welds go. 

One question, based on the left/right extents of the rust, I can take a a few inches off of the width of the new pan in each direction, eliminating the spot welded seam at the rocker.  I can also remove a few inches from the rear.  Would this be considered advantageous or should I weld the pan as-is with minimal triming?  Thanks, Tom

[Ridge Runner 1,112]

Dont use any more of the patch than you need ,i have had to redo patches where the Whole patch panel was used  and it makes it hard because the next time it has to be done the patch panel will not be big enough ...just thinking of the next poor shmuk in 40 or so years haha

[TomM 25]

Good point Ridge Runner.  That takes care of three of the four sides and just leaves the seam at the rocker.  If I feel comfortable with the butt weld I may eliminate the seam on that side.

Thanks, Tom

[SWPruett 83]

A butt weld is the only proper way to patch sheet metal in 99.9% of the cases.  It's much stronger, and more durable than a lap joint and when properly executed and finished, you will not have to worry about future hidden corrosion rearing its head years down the road.  And no matter what you do, a lap joint WILL corrode over time.

[latoracing 256]

I had a little bit of work to do on a '70 convertible and it needed a few patches. The picture of of the replacement part that Tom posed would make a good place to get the butt weld patches he needs to fix his floor. I personally would not put that part in as is, but fix the areas that need it. Here is a pic of the toe board sans the floor pan (and a lot of the inner rocker)after rust removal.

The area right in the corner of the top of the torque box had a hole rotted in it. That portion of the torque box lid was also removed and patched.

The welds ground down and the toe board was butt welded over this repair. All metal finished, and the repair should last a long time

Take your time, and it will be good as new. Good luck with your repair.

Mike

 

[TomM 25]

Mike, thanks for the pics.  I'm currently removing the rust with a wire wheel to identify the extent of the repair.  How did you remove the rust - abrasion, chemicals?

Thanks, Tom

[latoracing 256]

I tried Rust-B-Gone on this one, it works well.

Wire brushes are another good method, just depends on the area IMO

[TomM 25]

After a few iterations of Rust B Gone and wire brush I'm starting to finalize plans for my repair.  The red areas are where the rust needs to be replaced. The seam is a little suspect so I don't think I can get away with just replacing the red areas.  I see my two options as blue and yellow.  Is there any reason not to do the yellow?  Also, on the lower right I'd be welding through the grooves, I may consider going to the outboard edge of the grooves.

I think my replacement pan is 19/20ga.  I can only find 16ga and 22ga locally at Home Depot.  I've been practicing butt welds with butt weld clamps that leave a gap.  Not going to well to say the least.  This week we'll practice with no gap on both gauges to see if we can get comfortable with the butt welds.  If all else fails we'll do a lap joint but my preference is for the butt weld.

Thanks, Tom

 

[TomM 25]

 So what's the best way to ensure there is no gap for a butt weld?  I've been practicing butt welds and having much better luck without a gap, rather than using the butt weld clamps that result in a gap.  I've read that screwing the replacement pan onto the original and then using a cutoff wheel, but it seems like this would result in a gap equal to the width of the cutoff wheel.  I'm thinking I may be better off cutting the old section out, using it as a pattern to oversize the new piece and then grinding to fit.  I'll be replacing a fairly large section of the front passenger floor board, as seen in the photos.  Thanks, Tom

[Midlife 814]

I've found that almost no gap is about right for butt welding 19 gauge steel.  I use a grinding wheel to shape the patch to the hole so that it just fits inside on all edges.  I then use a large magnet to hold it in place and then tack-weld the patch.  Remove the magnet and go for it!

[TomM 25]

Thanks Midlife.  We cut out a 14" x 14" section of the floor today, just need to cut out the remaining 10% on the toe board this week.  Fortunately the pass/front section was only $35 so if I can't get the butt welds working I'll buy a new pan and switch to the lap joint.  Thanks, Tom

[mwye0627 44]

On 3/17/2018 at 11:16 PM, SWPruett said:

A butt weld is the only proper way to patch sheet metal in 99.9% of the cases.  It's much stronger, and more durable than a lap joint and when properly executed and finished, you will not have to worry about future hidden corrosion rearing its head years down the road.  And no matter what you do, a lap joint WILL corrode over time.

I always prefer to do a butt weld, but I also like to back it up with a Copper Backer Plate wherever possible.   The weld will not stick to the Copper, and makes it much easier to fill any holes and burn-through with the Copper acting as a heat sink as well as a backer plate.      I took a 3/4" Copper Tube, and flattened about 6" of it it with my Hydraulic Press so I have a Copper Backer with a handle good use in for most areas...

[bigmal 225]

38 minutes ago, mwye0627 said:

I always prefer to do a butt weld, but I also like to back it up with a Copper Backer Plate wherever possible.   The weld will not stick to the Copper, and makes it much easier to fill any holes and burn-through with the Copper acting as a heat sink as well as a backer plate.      I took a 3/4" Copper Tube, and flattened about 6" of it it with my Hydraulic Press so I have a Copper Backer with a handle good use in for most areas...

That sounds like a really intersting technique. I will give that a try next time. Thanks.

[aslanefe 333]

7 hours ago, bigmal said:

That sounds like a really intersting technique. I will give that a try next time. Thanks.

If you use copper tube as backing, make sure you make a handle from something that does not transfer heat fast. Copper tube piece heats up real fast.

[unilec 57]

Once you have the area cut out, lay the new panel across the cutout with a sheet of paper taped to the underside and from under the car use a marking pen to trace the outline of the cutout as well as the frame rail. This will give you a cut line for the butt weld, as well as where to drill holes to plug weld to the frame rail.