I got 2 holes rusted through my driver's side floorpan :(

ghunt81 said:

It doesn't get driven in winter. The rest of the car has very little rust except for this particular spot.

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Your car looks great and has a nice collection of mods to be proud of so if I was in your shoes, I'd have the rusty floor panel replaced and do the car right.

eighty6gt said:

what about chicken wire and expanding foam

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Pentalab said:

Excellent idea ! Better yet, just construct the entire car out of bondo.

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Laga said:

The floor of my `79 Mustang rusted out so bad in less than 10 years, that the drivers seat, with me in it, fell through to the road after hitting a large pothole. Maybe covering up the rust in the beginning with roofing cement wasn't the greatest idea.

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You should have just made it a Fred Flintstone car.

ghunt81 said:

It doesn't get driven in winter. The rest of the car has very little rust except for this particular spot.

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That makes a huge difference for sure!
Decades ago, I repaired a daily driver floorboard rusting under my feet, the really old fashioned way, whatever piece of metal was handy, rivets and roofing cement. Even after the fix, if I went over several inches of water, I would literally feel fine mist on my face! Water was pushing it's way through the repair, insulation and carpet.

I don't think your rust is quite as bad!

Its easy to spend someone elses money and tell them to have the entire floor cut out and have a brand new Ford floor pan welded in. But is that really necessary? Is this some special car that needs to be fully restored for some historical value? Or is it just one of a million Mustangs thats pretty nice and is regularly driven?

If it were mine, I'd do exactly like I originally said. Since I'm not that good of a welder, especially on sheet metal, I would make a patch panel and pop rivet it in. I would use spray on undercoating and maybe seam sealer under that. I would not use POR. It dries hard and rigid and is not the right coating for sheet metal that will flex a little.

I had many cars in the 80's and 90's with rust issues. They all did back then. This is nothing extreme and does not require a $3000 bill from a body shop to replace the floor and do it "right".

Racer47 said:

Its easy to spend someone elses money and tell them to have the entire floor cut out and have a brand new Ford floor pan welded in. But is that really necessary? Is this some special car that needs to be fully restored for some historical value? Or is it just one of a million Mustangs thats pretty nice and is regularly driven?

If it were mine, I'd do exactly like I originally said. Since I'm not that good of a welder, especially on sheet metal, I would make a patch panel and pop rivet it in. I would use spray on undercoating and maybe seam sealer under that. I would not use POR. It dries hard and rigid and is not the right coating for sheet metal that will flex a little.

I had many cars in the 80's and 90's with rust issues. They all did back then. This is nothing extreme and does not require a $3000 bill from a body shop to replace the floor and do it "right".

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Agreed, this would get nothing more than a quality quick n dirty from me.

Racer47 said:

This is nothing extreme and does not require a $3000 bill from a body shop to replace the floor and do it "right".

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Who said anything about sending the car to a body shop? It would cost a lot less to learn some welding skills and they'll come in handy for other projects.
You could rent/borrow a plasma cutter to cut the rusted piece away, grind the edges smooth, and use a piece of cardboard as a template for a new patch panel. Nothing beats the satisfaction of a job well done when you DIY.

I'll see what I want to do when I get in there and work on it.

Honestly welds seem to attract rust...I do have a welder, but it's a flux core so it throws splatter everywhere. Might be easier than drilling a bunch of holes for rivets though. I dunno.

The old adage comes to mind. "Do it right the first time or be destined to do it over and over again."

Seems like a nice car. How much is it worth to you? As suggested you could go out and find a piece of flooring from another car, cut out the rotten area; prep it and then give it to a welder to weld in the new piece. Doing most of the prep work yourself will significantly cut down on the expense. Most any good body shop welder or even muffler shop should be able to handle that kind of work. Additionally, Craig's list or other sites advertise welding services. Likely, very reasonable compared to a body shop.

Here's just one example from my area:

https://akroncanton.craigslist.org/sks/d/rootstown-welding-services/7278082304.html

Muffler shop

Well, leaking cowl grommets are no joke. This is what the floor looked like after I pulled up the carpet. The driver's footwell is completely shot and will need replaced but thankfully the rest of it is surface rust. Passenger side is also rusty but not nearly as bad. Figures that the rusted through part is directly over the fuel and brake lines...

That sucks, hate to see cars/trucks rust like that

ghunt81 said:

Well, leaking cowl grommets are no joke. This is what the floor looked like after I pulled up the carpet. The driver's footwell is completely shot and will need replaced but thankfully the rest of it is surface rust. Passenger side is also rusty but not nearly as bad. Figures that the rusted through part is directly over the fuel and brake lines...

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that stinks, a lot more that I expected to see. I thought these cars were galvanized?

ghunt81 said:

Well, leaking cowl grommets are no joke. This is what the floor looked like after I pulled up the carpet. The driver's footwell is completely shot and will need replaced but thankfully the rest of it is surface rust. Passenger side is also rusty but not nearly as bad. Figures that the rusted through part is directly over the fuel and brake lines...

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Mine looks exactly like that
Put it away in November wanted to get it out and realised it. I’m in Europe though so it’s harder to Organize parts or find a diagram so I know what parts I need. I haven’t looked for the cause yet but I guess my first look will be the grommets.

Badd GT said:

that stinks, a lot more that I expected to see. I thought these cars were galvanized?

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Ford should have spent the extra few bucks to galvanize the entire car. On a side note I have experimented with cold galvanizing spray from several companies. The rustoleum brand, sold at home depot, works damned good. Dry's super fast, so additional coats can be applied. Not one speck of rust on any of the welds underneath the car..... from years ago. Also used it in the trunk, when the steeda rear stb was welded into place. Also used it on several outdoor projects, same deal, zero rust. The other brands I tried, and bought at local machine shops, industrial suppliers etc, did not fare too well.

This all reminds me that it's time to change my fuel filter.

Gregs197 said:

View attachment 76981
Mine looks exactly like that
Put it away in November wanted to get it out and realised it. I’m in Europe though so it’s harder to Organize parts or find a diagram so I know what parts I need. I haven’t looked for the cause yet but I guess my first look will be the grommets.

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Weird how similar yours is to mine. The flanges on your crossmembers look terrible.

So on mine I took a brick chisel that I picked up at the hardware store and went over both sides and knocked off all the tar-looking sound deadening. If it has rust under it, it will pop right off- was actually easier to remove than I expected, but just know any of that in rusty areas will have rust under it as well.

I bought a steel plate and a panel flanger to make a patch panel for my driver's footwell. That is going to be tricky to cut out the old metal because it is spot welded all along the subframe. I have a spot weld drill bit but that is just too many to drill out especially since most of them are under the car, so right now I'm not sure how I'm going to tackle that.

BTW- I covered the dash and what I could of the rear area of the car with old sheets to at least keep some of the crap off them. Going over that rust with a wire brush on an angle grinder sends up tons of dust. I have been doing it with a shop vac running inside the car but it can only do so much. Plan is to clean off as much of the rust as I can, patch the floor, then paint it all with Rustoleum rusty metal primer (with a brush), put on a coat of Rustoleum paint (also with a brush), and then apply sound deadener. I have a small amount of POR 15 that I will probably use on the underside of the patch panel.

Noticed the thread and decided to take a look at my son's car. Found a bit of rust on both sides under the carpets. Not too bad except for a hole in the back corner (driver's rear seat) towards the outside of the car. The metal just flakes away from the bottom. Probably 2" x 3" all told but haven't investigated all that far yet. Appears part of it started up front on both sides so likely came from the windshield cowl grommets. I carefully siliconed all of them, let try and then sprayed the area with water as well as both driver's and passenger's windows for several minutes. No more water that I could find. Let it sit overnight and checked again before buttoning up.

I think the hole started on it's own from the bottom up (likely from salt corrosion) as the metal inside seems strong while the bottom just flakes away. Guess we'll find out to what extent when the body shop tears into it next week.

Still cleaning surface rust on the floors and picked up a couple of cans of cold galvanize. Will finish that work this week... then take it into a body friend of mine to get the hole fixed and check the rest of the car for any trouble spots. I've found the best way to take care of surface are those paint stripper (carbide) wheels you can get from any hardware store (Harbor Freight) on a drill. Makes quick work of it without too much dust.

Thanks for the tip on the sound deadening materials. Like yours portions of mine just knock right off with a chisel so I still have some work to do. Really glad to find it now before it gets like some of the pictures posted above.

To protect after cleaning/repairs (on the inside) I'm going to go the cold galvanize route followed by a couple of coats of primer/sealer/paint and sound deadener (80 mil). On the outside the body shop will repair the hole and check for any other issues. Then I'll cold galvanize everything followed by undercoating the entire thing with something that'll stand up to the weather/snow/ice/salt up here in the nothern climes (if even such a thing exists). Suggestions anyone? Roll on rubber compound/truck bed liner/Por-15/fiberglass/other?

A few pics: The black is rust converter but I'm going to take it back down to bare metal again in the trouble spots and cold galvanize the entire area. Hopefully, I don't find anything else major. ;D

So, after noticing that the driver's floor board felt thin when knocking on it I decided to chisel off the sound deadener (similar to ghunt); then used an abrasive wheel to clean off the rust followed by rust converter and cold galvanize. Then, wanting to make sure this fix will last I put down 3 layers of fiberglass mat. Floor seems pretty good now. So, now I'll concentrate on the underside taking care of any rust; convert/cold galvanize and then follow up with undercoat/truck bed liner. As I said I do have one hole in the back corner of the driver's side so I'm going to have that professionally repaired. The rest I have no problem doing myself. Let's hope this fix will last awhile (like until my son sells it). Not the prettiest fix but I'm no fiberglass expert...it's solid though. May/may not put buytl sound deadener on top. Going to leave it as is for the body shop so they know the score. Will decide that after the hole is repaired.

I started cutting out the bad part of the floorpan tonight. This thing is going to be a pain in the ass. Spot welded to the subframe right down the middle and of course the brake and fuel lines are right there. Nicked one of my brake lines with the cutoff wheel despite trying to be careful. Sigh...

Going to be a bitch getting access where the frame runs fore/aft through there. Looks like that back pan needs rehabbing as well.

For all... Recommend add checking grommets and floor pans to the list of maintenance items to look at every so often or once a year if you live in northern climbs or where they use salt on the roads. In my case I had the car professionally undercoated and still ended up with major damage. Only thing I've found that truly stops it (once it gets going) is cutting out and replacing the worst parts with mold-able plastic (comes in sheets, about 1/8 - 3/16" thick, sticks to everything; once dry is super tough/strong and impervious to salt. Very inexpensive. I had both quarter panels done (common rust areas) and they've held up great. I'll get a pic and post details after I visit the body shop). Either that, or replace the section with new metal.

Got the worst of the floor pan cut out. Lot of work with the cold chisel to cut all those damn spot welds. Still have to go over it to clean it off a bit more. Also made my cardboard template for the patch panel. I'm thinking I may do a few small welds and pop rivet the rest, I don't want to weld this whole thing.