Floor Pans Repair 101
Floor pans woes got you down? If you got the time and the tools, replacing those rusty floor pans can save you money as well as being a pretty fun project (depending on your definition of fun). I threw this tutorial together quickely to help anyone out looking to replace a floor pan on the cheap. The welds are not the best or the prettiest (as i wasn't going for perfection)...but for the purpose of this demonstration...it will do. You will be able to apply these techniques to any make or model floor pans.
Lets get started : )
Tools and Materials:
1) Replacement floor pans [or sheet metal to patch rust if full pan replacement is not necessary].
2) MIG Welder of the 120v or 220v variety. You can get by with a cheapy flux core from Harbor frieght if your short on cash...but...i REALLY recommend MIG for this job. Usually anything of the lincoln, miller, Eastwood variety are a better value for your money. If your doing this job, you'll probably be welding someting in the future so...spend money once is what i say.
3) A hole punch / flanging tool for punching holes for spot welds and flanging panels. Pictured below is a Harbor Frieght air hole puncher and flange tool. Pretty nifty tool considering you'll have a lot of holes to punch.
4) Cleco Pins and/or Sheetmetal screws. Before you finalize the welds into the panel, the panel must be secured to any floor braces and/or transmission tunnel.
5) Cut off tool. Cut off wheels work great but in a pinch a sawzall will get the job done but be careful not cut through any floor braces or support structures.
6) Grinder to grind down the weld beads.
Start with some clean scrap 18 gauge sheet metal. Consider this to be the *new floor* pan you'd be installing. I HIGHLY suggest you try this method with scrap sheetmetal BEFORE you try welding in your pans. Use this time to dial your welder in and practice your technique. It's easy to blow through thin sheetmetal and blowing holes through your new floor pans is not a pleasant experience. It's easier to practice first...then fix it later.
Clean the metal off of all dirt, grease, and mill scale. Brake cleaner works great for this.
Measure a few 4" or 5" strips with a sharpie and ruler.
This is a sheet metal shear and an invaluble tool if you plan on working on other sheet metal projects on your car. It makes cutting sheetmetal a breeze and cuts down on the sparks of cut off wheels.
Cut the 4" or 5" strips.
You should end up with 2, 4, 6, 8, [how ever many strips you want to use to practice]. You need an equal amount of strips to practice with as one piece will be the *old* floor or support surface and the other piece will be the *new* floor pan being welded in. I suggest trying it atelast twice to get the swing of it if you've never done floor pans before. So that's a minimum of 4 pieces you need.
Ok, so now you have your pieces. Mark one as old floor and one as new floor pan. In you project...you'll have to cut out the old rusted floor pan out of the car. Sometimes the rusted section does not require you to remove the ENTIRE pan up to the rocker sills or the trans mission tunnel. If this is the case, then you will most likely be installing the floor pans using the overlap method [see below for more info]. If the entire floor pan is being replaced, this tutorial will differ slightley as the new floor pan you are installing will likely be plug welded along the rocker sill and floor braces.
When doing an overlap floor pan replacement, your new pan will overlap part of the old floor pan as pictured above. In most cases, it is suggested that youe keep AT LEAST an inch of the old floor pan material around the diamter of the repair section to weld to. The flange you will be making is half an inch so that one full inch buys you a little wiggle room should your measurements come out wrong and you need to adjust accordinly.
The new floor pan will need to be welded to the old floor pan surface somehow. Here is where many *schools* of thought vary on exactly how you should achieve this. Some say you should butt weld around the entire area of the reair. Other say, you should plug weld the new pan in and call it good. There really is no right or wrong answer, but it does really depend on the situation and the condition of the availible metal left from the old floor pan surface. I will say this...if this is your first go around with welding or floor pans...overlapping and plug welding the floor pan in is WAYYYYY easier and has less of a chance of you screwing up and blowing holes through the butted pieces of metal.
Take your flange tool and flange the OUTER lip of the new floor pan or patch piece. I like the air flanger because it is quicker and gives you a consistant half inch flangg without any guff.
Once you've flanged the outer lip of the pan it should look like this.
It is ESSENTIAL...that you flange the new pan the correct way. The new pan must sit ON TOP of the old floor pan surface so it must have the flange like this. If you mess up and do it the other way...the new pan will be RAISED from the old floor pan surface instead of flush with it...as you want it to be.
After you get you flanges done, you'll lay the new pan in where you cut the old pan out. It will essentially fill the hole and lay flush over the old floor edge that you left. You remembered to leave at least an 1" right : )
Time to punch some holes for the plug welds. I like the air punch because punching hole by hand jus takes for ever and will give you hand cramps.
Now how many holes you punch...is up to you. I like to put a hole every one to one and half inches. Sure it makes for more welding, but at the end of the day, you're floor will be properly fused to the old surface and strong as ROCK.
Now that you got your holes punched...its time to lay the pan back in the hole and recheck your work. This is what you will see...the new floor over the old floor ledge and holes waiting to be filed with welds.
If all is good and you're satisfied with the fit, its time to snug that baby in and get ready for welding. Depending on your situation, you may be able to clamp it in certain areas. More and likely though, you will use a combination of sheet metal screws, cleco pins, and clamps. I like to screw the floors down to floor braces as well as the out edge of the new pan to suck the floor pan flush to the braces and the old floor pan edge. Having a flush fit is essential to getting a good weld as well as fitment. Once you start welding the new pan will want to move on you in ways you never thought (due to the heat of the welding). The best thing to do is screw in sheet metal screws in a few [or as many] of the punched holes as you need to secure the floor. Once the floor is screwed and clamped in...your ready to weld.
18 guage [or whatever thickness the new pan is] is very easy to blow hole through if your overzelous with the heat of welder. Most welders have charts on the inside of them with settings that are good starting points for various thicknesses of metal. In this example, my tapped Lincoln Weldpak called for a B voltage setting. You will also have to set the wire speed for the welder. This is shown by the following photos. To sum it up, wire speed is the current of the weld and control how much material is fed into the weld. To slow and you get bad welds....to fast...and the wire will push back out of the weld pool...give you bad welds. Dial the wire speed in by adjusting the wire speed if you have the voltage set arleady. A proper weld should sound like frying bacon....zzzzzzzzzzzzzzzzzzzzzzzzzz
After you've made some practice beads [playing with different settings on the welder]...inspect the beads. Some of them will look like bird poop...some of them *hopefully* look good. If the welds are raised and sitting on top of the metal...that means the weld was too cold...turn the votage up. If you burned holes through the metal that means the voltage was too high...turn it down. You're looking for the PERFECT settings so you get penetration and proper fusion...but not blow through.
One way to tell if your getting penetration is by flipping over the test piece and see if it penetrated through. Here you can see that the weld penetrated the base metal but didn not burn through. You can also see the HAZ [Heat affected zone] around the weld bead. This is what you want to watch out for as the HAZ is what causes warpage if you go over board with the heat.
After you get the welder in....lay though plug welds. The goal is to fill in the holes with weld. Some straigh straight in the middle of the hole and weld until the hole is full of filler material and has a nice crown. I myself like to start the weld outside the hole and circle in and fill the hole. I think it fuses the metal together better and helps tie the new and the old metal together better [in addition to letting the weld pool heat up before filling th hole in with weld].
While most of these welds look terrible...this is probably what you will end up with your first test piece. See how some of the holes arent completely filed in and have holes...this what you dont wont. If you do end up with holes that arent completly filled...its ok to go back and hit it again with another weld to fill the hole in completely. The goal is to fill the plug welds ENTIRELY.
The last weld to the right is an example of a proper flug weld. Completely filed and almost flush.
This is what the flip side of the base metal [old floor section] would look like. You can see it has penetraded by the circle marks and the HAZ.
Once you're plug welds are done...sit back, crack a beer, and marvel at your new floor : )
You can leave the weld beads as they are...or grind them down if your going for an invisible repair.
Last but not least...seal up the weld and lap joint with a seam sealer. This ensures that water and junk does not get down in the new metal. If not, you'll be back in the same boat in a few years as water will work its way in between the seams and start rusting all over again.
This is not an all inclusive on how to replace floor pans but the steps listed above covers the major aspects of floor pan replacement. The most important thing, especially when doing it for the first time is...TAKE YOUR TIME AND THINK IT THROUGH. Take your time...measure twice...cut once...and GET-R-DONE