Greetings,
I'm fairly new to the forum, been soaking up the vast knowledge available.  But I've been getting lurker's remorse, so I figured I better post something (hopefully) helpful.  I bought a 96 tracker about 2 weeks ago, and have been going through it and fixing the areas that need attention.

My first project was to fix some door sill rot.  The rocker panels themselves are in decent shape, so I only needed to do some patch work.

Ok, so there's some light rot, and it looks like the previous owner gave it a bondo bandaid.  First step is to remove the paint, and see what's really going on.



I've found that a rust/paint stripper attached to a high speed drill like the one pictured below worked better then even a wire wheel attached to my grinder.



Once I've accessed the damage - not too bad; I decided to cut out the bad piece and weld in a new one.  I used a super thin cut-off wheel on my grinder and cut out a nice rectangle section.  This should help making the fabrication of the new metal fairly easy,  just a rectangle with a straight bend.

*take note - all of the rear vehicle's wiring runs through here. So be careful cutting, and even more careful when welding.

Now I haven't really welded anything before, I once played with an old arc welder, but that was years ago. but I figured I'm mechanically inclined - how hard could it be.  So I got some basic instuctions from my brother borrowed his mig welder, and proceeded on my way.  He left me with on piece of advise that certainly held true. "You don't have to be a good welder, but you'll have to be a great grinder".  Oh - so very true!

Before you start welding:

• Remove all paint and rust a few inches from where the actual weld is going to be.  A mig welder really needs nice shiny metal to work well.
• Disconnect your battery
• Make sure you have a good ground - I found the closer the ground is to the area you're welding the better.
• Position your patch and tack in it place,  just a couple in each corner.
• Make sure it's still in place, and proceed to work tacks around the patch.
• If you try and run a bead it will warp the metal, so stick to tacking it or at least short 1" beads

Here's my first attempt.  The plate shifted to the right, and was also much lower on the right.  I wasn't happy with this.



I primed it to help get a better look, still don't like it.  I decided to cut it out and start again.



Continued below...

The most difficult part to welding a patch of this nature - is the super thin metal, especially after it's had some rot.  I had the welder on the lowest setting, and the wire speed set high.  I still burned alot of holes as I went. The trick is to get a couple good welds built up, let it cool, then come back and work from those welds.  Takes a bit of practice to get good at this but it's not too bad.



Notice the hole in the center of the replacment metal.  I used a screw as a handle to help hold it in place.  Still a couple of holes, but much better then the first attempt.

I grinded everything down, and ran another bead around it to close up any remaining holes.



Once you're happy with the results grind it all down.  My brother said, "hit it with a hammer if it stays in place then your good!"  It past the hammer test.



Spread on some bondo to finish it off.



Sanded and primed - it came out pretty good, the lines all match, and it's good as new.  I actually started with a rust converter to stop any other rust, mainly around the body trim holes. 



I finished it off with truck bedliner for ultimate protection.

nice repair!
well described, also. thanks

Great job!  It inspires me to get to the rot on various parts of my vehicle, and there is lots of it since we have lots of road salt put on the roads every winter.

Thanks,
Yeah, lot's of salt here as well.  I've got a couple more spots to fix.  Some really bad rot behind the passenger side fender. lools like it's actually part of the cab.  Also, the second to last ladder in the frame has rotted through, and some there's light rot in the compartment behind the taillights.  Those I just clean up as much as possible and hit it with some rust converter.

I know the spot you are talking about.  I pulled the passenger side fender to do some work on it and found the same spot not only rusted, but rusted through.  I am considering my options.  I will either cut out all the rust and try to weld in something, but with it seeming to go right into the cab area I may instead fix it with fiberglass once I am sure all the rust is gone.

Both of my rear tail light mount completely rusted out.  I fixed the one by getting creative with some sheet metal, but now the other one has rusted out I am trying to decide how I want to fix it.  I may try to find a kick or tracker that is not as rusty but has a shot drive train and do a body transplant (at least in part).

Oh, one place to check is under the rear carpet.  I had a couple of spots that rusted through there.  Yet another area I need to fix.

i am fortunate to have a mostly rust free kick, and just keep painting the rust i do see.
that rust converter stuff is real nice, and i have also done the fiberglass/bondo "repair" on other vehicles, and it has been good enough for me.
i kept a whole rear body section alive on an old fiat i had by drilling small holes in strategic places to spray wd40 inside it, as it was rusting from the inside.
i like your approach, and will try it next time.

Hmmm, fiberglass repair doesn't sound like a bad idea. I'll have to remove that fender and see how bad it actually is.

I'm debating, when I go to fix the rear frame ladder, if I should pull the entire body off, and fix/rust proof the whole frame, or just fix the ladder for now.  I guess time would be the factor, of course if pull the body, I could install a body lift in the process.

I have never considered taking the whole body off.  I would not even know where to start to get it off, not to mention not knowing how to lift the body off the frame.  I would love to do it simply to get at the frame, which is in pretty good condition, and clean up the rust and paint it.  Yet more to learn.