View Full Version : Repairing Floor Pans
10-07-2007, 06:06 PM
I just got a new HH140 with gas and want to repair and/or replace some metal in my 66 Fairlane floorpans. I want to know when to repair and when to replace, does someone have a good rule of thumb to go by? I've seen a few small holes here and there, but no large holes. It seems be pretty solid for the most part. I'm going to strip out the seats and carpet soon and see the full extent of the damage. My plan is to repair it and clean it top and bottom and put some rust preventive primer and a couple of coats of good paint on everything this winter.
10-07-2007, 07:02 PM
I guess that depends on your definition of "Small Holes"...are they smaller than a pencil eraser? Are they random, or are there groups of them?
Small little ones can be overcoated with a coating like POR 15, and little pieces
of fiberglass mat used here and there to bridge the holes. I've done whole interiors some antique cars this way, and they looked great afterwards. If you have a lot of perforations, or the floor "feels thin", you can use the method I grew up with in New York, where you could not stay ahead of rust, it seemed. That method was "smear the area with undercoating or roofing asphalt goop, and screw an old license plate over it.
It depends if you are going to "Restore" (and that can take along time, and cost a lot more than you ever intended), or "Patch". If the restoration is done in an amateur manner (and most are), its really of no value when then car is sold...except maybe to another amateur!
Then again, cutting out the bad and putting in metal patches is great welding practice. Entire pan replacement is the costly, professional way, and can be very difficult.:)
Where are you located"? You don't tell us in your profile.
10-07-2007, 10:27 PM
I'm in Alabama, close to Huntsville in the northern part of the state.
Most holes I've noticed are pinhole size up to less than the size of a pencil eraser. Some are close together but not what I would call clustered. I do have one spot in the trunk floor about the size of a golf ball. I know I will definitely patch that one. The rear trunk seal had a gap in it letting water drip in one little spot every time it got wet, I guess. This car was bought new in Birmingham, Alabama and been here it's whole life. The underside is very clean and mostly rust free.
I've had the car for about 20 years, garaged 99% of the time. I'm planning to keep it a while longer, too. I want to do a little project every year to improve it. Last year was the front end and disc brakes. This year new clutch and repair the under carriage and floors. I may do the rear end and exhaust, also.
10-11-2007, 07:57 PM
If the pans are in good condition overall but with small rust holes another option is to clean everything up with a wire wheel and fit some sheet metal patches on top of the existing floor pans. Drill holes throughout the patches and use the mig to plug weld the patches in place.
I'm replacing the floor pans in my 68 Mustang now. I've replaced some areas and double plated others.
If you add patches on top of the old, do it from the inside where it will be under the carpet. Be sure to use a good paint or under coating on both sides.
10-12-2007, 05:48 AM
What is your end goal ?
A daily driver or a 100pt resto ?
For a daily driver you can cut out the cancer and patch but if your aim is to have a 'show car' there may be places that sell complete pan replacements,
Year 1 comes to mind.
10-12-2007, 07:40 AM
Forget the small holes. The question you need to ask is ... how much metal is left around them. How thin has that metal become. I generally use an auto centrepunch. Pop it right where the holes seem to cluster. The depth of the dent left will tell you how much strength you've got left. If it punches right through .... you know. A '66 was built with pretty thick metal ... so if you do replace, don't go with cheap 22Ga pans. Hold out for the good ones.
11-07-2007, 10:53 PM
I recntly patched some holes in the floorboards of my '50 Ford. It had rusted through right where the floorboard meets the firewall. Like the Professur said, it's all about how good the metal is around the holes.
I used a cut off wheel and squared up around the holes back far enough to get to solid steel. This left a good clean solid square edge to work with. Then all I had to do was cut some sheet into the proper size squares and rectangles and weld them in.
11-10-2007, 03:06 PM
My tips would be to 1. make sure your patch is covering all rusted out metal in the area, so you don't end up with a hole right next to your patch that you have to fix next year. 2. Paint or undercoat when finished. 3. Maybe this should be 1, watch out for fire hazards like your gas tank etc.
11-10-2007, 10:01 PM
Thanks to all who responded. I will keep you posted when the project begins. I will probably start in the next few weeks. I'm looking at everything now to decide how to go about it and what I should replace while the interior is out.
11-11-2007, 09:23 AM
do it right or dont bother. whatever you do dont lay anything over holes and screw or weld it down. from the underside it is just going to trap things like road dirt and mosture and just continue rusting. i would attack any area there is any loose rust with a wire wheel and evaluate what you have. you have to kill the rust before going any further, like said you can just fiberglass mat over it all if the floor is still strong. not my choice thing to do but it will work. you have to make sure you stop all of the rust and seal it from the bottom with a good paint. i like to weld in new metal any time it is possible, remove the rust and make a patch to fit the hole you cut out. weld it all around first with a bunch of tacks then welds no longer than an inch at a time allowing it to cool. it really isnt that bad to replace the floor pans, if they are available, but if you just have a few small holes its probably not worth the extra time and effort. when done coat the top and bottom with a few coats of paint and primer, undercoat if you like, im not much of a fan of undercoating either.
01-10-2008, 12:05 AM
I prefer the plaster and rivet method myself with old monsters since there is no beating the rust monster. Still if you want to resto it get out the mig or tig. These guys know their stuff and check out the how to section.
01-10-2008, 01:31 AM
So, how's the floor pan going? Hopefully, you have had a chance to get started, anyway. I will be starting the process of completely replacing the floor pan in the project truck, and will be documenting it as completely as I can. However, it will be all custom, with some OEM touches. Too bad you aren't close. You could come to the get-together and see how it's done, and even bring your beast and work on it. It's not really a get-together to work on my truck; it's more of a very hands-on class in metal shaping. Later in the year we'll be fab'ing all the body panels from scratch. Anyway, take some pics as you go so we can see the progress!
01-10-2008, 07:40 AM
Floor pans are readily available for old Farilanes and Mustangs. I have a 66 mustang and to replace both sides of the transmission tunnel from front to back will only cost around $100. The seat risers are another $35/side if you need to replace the toe boards that run up to the firewall that will be another $50 or so. It really isn't too difficult of a job just a lot of spot welds to drill out and then a lot of tack and plug welds to do. Keep us posted and post some before and after pictures. If you haven't started yet, post some before pics :)
01-18-2008, 01:24 PM
Please, take a look at some of the pics at this site
The rear floorpans are still very strong, the dark rust spots are pinholes or just starting to pit. There are only two or three larger holes. I can get floorpans for this car and cut the rears and sell the fronts. What would you do?
01-18-2008, 02:20 PM
Well, having the ability as I do now, to form sheetmetal, I'd cut out the sections where it is really bad and form new patch panels. Without that ability, I'd probably cut out the bad sections and replace with a repro patch. I would not weld a patch over the old stuff. If the holes are in relatively flat or at least non-complex areas, I'd probably even try to create patches myself without the right tools. I think you'd be surprised how easy it is to make some of these patches.
Just my 2.4¢.
01-18-2008, 03:00 PM
So, what i think your saying Whatego is i can use a cutoff wheel and cutout the bad, use that piece as a template and create a patch. Should i use a flange tool and plug weld? Thanks for your help. I want to try to bring the car back to as close as factory condition as i can.
01-18-2008, 04:03 PM
The purist thing would be to butt weld the patches in. However, it can be tricky sometimes to do so. The easy way out is to flange one piece or the other and plug weld, or even weld the lap joint, which would do a better job of sealing. Either way, skip around to keep the heat from building up in the metal.
01-22-2008, 03:17 PM
I bought full length floorpans for my 69' Firebird and lapped it with about a 1/4 to maybe 3/8 inch lap (to the inside) and welded the entire perimeter using a jumping around technique to keep the heat low. I did both sides it looks great on the inside of the car.
Underneath take a small body hammer and tap the metal close to the surface and buy some "Duraglass" strand reinforced filler....Like concrete when it sets. smooth the floorpan & DA sand it underneath....Paint and undercoat and the car will appear as new. My car is rock solid and has no creaks or "Oil canning" and the seat pans welded back in nice and once the welds were ground inside it was pretty much eye pleasing. I liberally applied black rustoleum to all floors after I'm finished...If its a trunk floor you can splatter paint it over the rustoleum...REMEMBER that spatter paint is NOT waterproof.
I also used 3M weld thru primer between the lapped panels to prevent future rust.
I just patched the drivers side rear seat footwell on my 74' Monte and the patch panel from "Parts Place" in Chicago fit excellent. I drilled holes through both panels, 3M weld through primed and plug welded the pan in holding a chunk of brass up from the bottom of the floor so I could control my plug puddle better. It's pratically non-noticeable and its a lap-weld with plug welds!! I ground the surface of the welds so they were practically invisible. I think the was no more than a 3/8" lap at any one point.
I like lapping them better than butt-welding them. My personal preference. Besides there is no weld hardly exposed underneath the vehicle and its easily finished out or hidden with seam sealer & undercoat.
Now if its a door corner or a roof rail or hood patch of course I butt weld it....So its a perfect fit. Many cars use lap welds from the factory to join firewalls the floors or trunk extensions to trunk floors...I almost never see rust through at those joints...usually.
100 point original...on a old car...To me thats a mental disease, Obsessive compulsive or **** or something. As long as the fab work is done with care and looks nice when its finished I wont critique it. Some cars were poorly designed when new....Why recreate a poor design? Ex: my rear side marker lights on the 74' Monte....welded them puppies up solid and replaced the light with a stick on "big rig" type reflector that appears factory. Its dumb to put a light right where the tires sling water on the seams...Rust is gonna happen again unless its fixed right. Which I did and its only noticed if I point it out.
01-22-2008, 09:39 PM
When you say lap joint did you use a flange tool and punch? Most pans that are available don't come up to the tunnel so the work there has to be patched. Do you have any pics of your work?
01-24-2008, 09:45 AM
I dont have any pictures of that type of work....not too glamorous and most people are jsut happy to know a car has new floors instead of rust holes.
I have never used any sort of flanging tool hand operated or air...I just made a good fit panel on top of panel in the most inconspicuous areas. Sometimes I shape the metal to make the fit better but not a actual flange.
Both the GM cars that I patched up had just enough of the tunnel base to lose all the rust. I did however make a trans tunnel box to make room for the Hurst shifter with custom linkage on my 69' Firebird. The car doesnt use a console and its quite a conversation piece and it looks good. I was made form hand formed and cut sheet steel.
I also put floors in my old 65' CJ5 Kaiser Jeep....The wood supports rotteds out the bracing. I made new bracing out of 1/8" wall 1" square tubing and then new CRS sheet steel...Painted it with thinned Hammerite and sprayed it on with a gun. It was really nice when finished.
The First car I welded on was a older trans am....I was real crude on it...I would find the hole underneath.....tack the corner of a flat piece of sheet steel and then hammer it to conform to the area and weld more and hammer more until the whole thing was formed like a bandaid. Worked well actually and all the welds were from the bottom up. (That car was on a hoist)
01-24-2008, 06:17 PM
This is the floor of the monte Carlo the entire area under the driver seat has been replaced about 24" X 24"
01-24-2008, 06:27 PM
The floor was painted with black industrial (Silver & black-gallon can) Rustoleum.
I did not use the seam sealer yet....I wanted to get the paint in there first...This is how the car looks at this moment too....I just got my bench seat back from the upholstery shop yeasterday and the new carpet and full weatherstripping kit is here. I also got a new black dash and many black face of the dash parts.
I have a line on some nice black door panels used and some nice black seat belts....The car will still have a few here & there green items and a green headliner... But a black car with black and green on the interior and dark tinted windows shouldnt look too bad...
I have the paint already....DuPont Centari, Pitch Black I also have a brand new set of Weld Draglites for the car 15X3 front and 15X8.5 rear with Mickey thompson front runners and 275/60/15 drag radials for the rear.