Before we get started on rust repairs it is important to go over some of the tools needed especially in the area of grinding the welds down smoothly and efficiently. Starting with the welder this Miller 135 is a great machine for performance and durability and it will weld from thin 22 gauge to penetrating 3/16th thick metal which is plenty for any project a Hot Rodder is building.
Grinding is a very important step. The 4 inch 10,000 rpm grinder on the left works well to "rough" out welds on high crown areas that are easy to get to. The green Cubitron disc last very long and it is 3M's latest technology. To the right is a flap wheel which is used on the same tool to finish off the metal very smoothly. No compressor needed with electric tools.
This is a Porter Cable variable speed electric buffer/sander tool that we use for grinding. They will turn 200 to 4000 rpm depending on the settings and how much you pull in with your finger on the electronic switch. We use it with a 10 inch Flap wheel from Norton. Because of the Surface feet per minute due to the large diameter wheel it removes material fast, leaves a nice finish and does not heat up the metal like a smaller wheel does.
If you feel more comfortable using smaller tools then the same Cubitron disc can go on this air powered " large angle grinder" on the left for a little more control with the same flap wheel to finish if need be. You need a minimum 5 hp or 8-10 cfm to operate it.
This is the most commonly used set of tools. Light weight and low cost. They are slower removing material but also safer. With the smaller size they can also get it to tighter areas. Rated at 10,000 rpm these are available from many MFG's. The common small angle grinder or die grinder as some call it along with the cut off tool using a 1/8th thick wheel. The cut off grinder is used to work the welds down to a very close level then the roloc disc on the angle grinder takes the welds down to a finish base metal level.
For hard to reach areas a belt grinder is a good choice and the mig tip cleaner keeps the welder performing at its peak.
The copper spoon on the right works great to hold against the back side of pin holes to keep the welding wire from pushing past the panel which retains a flush weld. The copper pad clamp works well when you have holes close to an edge.
As seen Luie holds the cut off at the correct angle to achieve the best results. This allows good sight and helps keep you directly on top of the weld and not dropping off the edge hitting the base metal. In addition notice how he holds his hands like a tripod against the panel. This stabilizes and allows more precise grinding.
This is what you are after with no base metal touched, only the weld.
The side angle shows when it is time to use the finish grinder such as the small angle grinder with a roloc shown earlier.
Once it gets down to this level it is time to use a DA with 80 grit on the grinder mode.
A DA or Dual Action sander in the grind mode using 80 grit sand paper finishes it off to this state.
The Orbital mode of the DA shows a perfect grind. No base metal was touched beyond the factory 20 gauge thickness.
TIME TO START REPAIRING SOME RUST. We start off with the typical pin hole. These will usually not show up until all the paint is removed and media blasting takes place. They are easier to repair then replacing a whole panel especially when full access from behind a panel is available. Spot touching them with a mig or tig welder is the best solution. If you are good with Ox and Acetylene then sweating a few drops of brass to fill them is also a good choice.
If needed you can use "copper" in various shapes flat, round, angles etc that fit your panel where you need to spot weld. This will keep the weld from pushing out on the back side. If you are good at welding simply spot tack around the hole and work your way in to fill it up. Becoming a good grinder of welds is the biggest challenge. The goal is to grind it smooth with out hitting the base metal around it to take it flush.
The next common area is where exfoliation takes place because of water that gets trapped inside a panel and slowly seeps in and around a folded seam. We media blasted to show what we truly have and we are ready to do battle. Doors and trunk lids are the most common panels with this problem. In order to keep from replacing the complete panel or outer skin, " if there even is one available" this is a good solid repair technique and will save time which is money.
The first thing to do is drill out any spot welds and gently peel back the edge so you can get to the trouble areas. Using a strong putty knife or thin bladed chisel to tap and lift or similar tool can do the job. As seen we then spot touched the holes and will now media blast the edge before folding it back.
Using a block of wood on the outer skin we can slowly hammer tap the edge back over or use pliers to squeeze it back tight. We then weld it back up.
A few tools that we use to accomplish this are simple flat pliers, sheet metal roofer seam pliers and other peel back tools.
Like any project stripping the paint off is the first step as things are not always as they seem. Here we see old Bondo that a shop simply filled in the rust with.
After all the filler was removed you can see they never cut out the rust but simply floated it with good old bondo.
Always make a template that will go past the rusted section a minimum of a 1/2 inch so that you have full thickness of the original metal to weld on.
We then cut out new metal in the same gauge as the original metal. Lay the patch on top and scribe a line on the outer edge of the new metal. Use a cut off wheel and trim right on the line, too tight 1/16th or less then when the heating from welding takes place it will push the two pieces together and swell. 1/8th and larger and the mig wire will not fill the void requiring too much welding and raising the chance of warping the panel.
Once welded you want full penetration like this shows on the back side. Once we run a grinder over this just a bit and then media blast it we can prime it for no repair detection.
After full welding and then grinding it smooth it is ready for a skim coat of polyester fill to perfect the panel.
Another area often over looked are the panel seams where the factory lead was applied like this qter panel to roof seam. These usually have traces of rust in them once the lead has been heated and scraped away. Unless you have extreme knowledge of lead repairs and are able to lead with out any traces of acid left over then the following method will work best. It will also stiffen up the panel and be a much faster repair at that.
Next we fully weld the seam then grind the welds smooth.
After we media blasted we then apply a thin coating of 3M #1838 green 2 part epoxy for permanent sealing. Note the tape to confine the epoxy. 1/6th thick is all that is needed.
Let it dry over night then sand it down and peck it with the media blaster and then apply a thin coat of Rage Extreme from Ever Coat. You now have a permanent repair that will never rust. EVER!
Floors are the next common problem. If you pull out the carpet more then likely you will see thin and rusted out holy sections.
On full frame cars there are braces that run from side to side and most of the time there are no seat risers to deal with. On uni body cars where the frame is welded in to the floor such as our demonstration car you have to remove the riser. If at all possible we like to keep the original risers because repro units are often inaccurate in height and angle which will make the seats sit crooked. NOTE, take height measurements from the edge of the rocker panel where the step plate was to the trans hump and also front to back so you know the proper re-positioning specs.
The next order of things is too remove the rusted floor sections as close and tight as possible past the rusted sections leaving as much room as you can to trim and fit the new floor.
As seen we placed the new repro floor on top of the original. The marker line shows plenty of material to work with. The shapes and grooves that the factory floor were stamped with are what we are mostly concerned with. We want to minimize going through them as much as possible because that would require more fitting and smoothing around them on the bottom side. The goal is as many flat areas as possible. As seen we cut the old floor out to avoid as many stampings as possible.
Our new floor would cover this entire toe board, however this was the only area rusted on the toe board. The original floor overlapped the toe board so we want to keep that original. The repro floor is only made in one section so choosing to install this small section is faster and smarter because then we will simply lay the main floor down on top of this seam as per the factory.
Once done we simply grind it flush and you have a nice repair.
Now that we have the smaller section repaired we media blast the outer perimeter including the frame rail to remove all traces of rust.
Next we Zinc Chromate prime the entire blasted metal area. This will eliminate any corrosion in the future.
We then clamp the panel in place for a tracing all around the uni-body frame rails. We then carbide scribed around the perimeter of all the bracing approx 1/2 inch inside the scribe marks is where we will drill holes for welding. That will put the weld dead center on top of the frame rail and bracing. NOTE ! As a safety procedure we tack welded a piece of tubing to keep the frame rail from moving in and out or front to back during the procedure.
With the floor panel pulled back out you can see the trace marks where we will measure inside a 1/2 inch to drill the holes for welding the panel on to the frame and braces.
In addition we traced around the old floor where it meets up with the new one and we are tape marking where to cut. This will allow us a butt fit to weld the new floor in.
As seen holes were drilled every 2 inches.
We have panel clamps in place where the old and new panels meet. We also used self tapping screws to press the new floor in tightly against the frame and braces before we started welding. This way when you look at the floor from the underside it will be super tight against the frame and bracing.
Once we had it all fitted we welded it up solid. Only weld 1/4 inch long beads then move on to another section and back to another area, sort of like chain links to allow cooling between rounds
As mentioned earlier we removed the odd seat risers. There are repro ones available but they can be inaccurate so choose wisely when replacement is needed. We like factory parts when ever feasible. These original seat risers require a repair section on the flange so we are ready to weld them in solid.
Installed we align to our measurements and mark the locations.
As seen on the ghost silhouette we spot blasted the old risers through the old welds we drilled out beforehand so we could get good welding penetration and mark its proper location at the same time.
Again we installed self tapping screws to get it tight to the floor and then welded it in solid. Once she was welded we simply removed the screws which left a 1/8th hole and then welded them also.
The floor is done and looks good. We usually hold a light on the opposite side and check for any pin holes where the light shines through and then touch them up if any to finalize the repairs.
Next we fully media blast and then epoxy prime the entire floor so we can go on to the next step of the build.